CASES OF THE MONTH
NEB-RELATED CORE-ROD MYOPATHY WITH DISTINCT CLINICAL AND PATHOLOGICAL FEATURES YOUNG-EUN PARK, MD, PHD,1,2 JIN-HONG SHIN, MD, PhD,1,3 BORAM KANG, MS,3 CHANG-HOON LEE, MD, PhD,2,4 and DAE-SEONG KIM, MD, PhD1,3 1
Department of Neurology, Pusan National University Yangsan Hospital, Beomo-ri, Mulgeum-eup, Yangsan, 626-770 Gyeongnam, South Korea 2 Biomedical Research Institute, Pusan National University Hospital, Busan, South Korea 3 Research Institute for Convergence of Biomedical Research and Technology, Pusan National University Yangsan Hospital, Gyeongnam, South Korea 4 Department of Pathology, Pusan National University, Busan, South Korea Accepted 2 November 2015 ABSTRACT: Introduction: Mutations in the gene encoding nebulin (NEB) are known to cause several types of congenital myopathy including recessive nemaline myopathy and distal nebulin myopathy. Core-rod myopathy has recently been reported to be another type of NEB-related myopathy, and is pathologically characterized by the coexistence of cores and nemaline rods within muscle fibers. Methods: We describe 2 patients with core-rod myopathy who were analyzed genetically by whole exome sequencing and evaluated clinically and pathologically. Findings were compared with those of patients with the disease of other genetic causes. Results: Three NEB mutations were identified, 2 of which were novel. Mild clinical features, unusual patterns of muscle involvement, and atypical pathological findings were observed. Conclusions: We propose that the clinical and pathological spectrum of core-rod myopathy should be widened. A significant amount of residual nebulin expression is believed to contribute to the much milder phenotype exhibited by the patients we describe here. Muscle Nerve 53:479–484, 2016
Nebulin is one of the giant proteins in sarcomeres. It spans the whole length of thin filaments and binds more than 200 actin monomers. In addition to maintaining the lengths of thin filaments, it is involved in cross-bridge cycling kinetics and in regulation of calcium sensitivity.1,2 Although mutations in the nebulin gene (NEB) have long been implicated in congenital myopathies, sequencing of NEB has been a challenge due to its huge size and the repetitive nature of its sequence.3 The recent advent of next generation sequencing (NGS) technology has facilitated access to large muscle genes like NEB and enabled interrogation of otherwise unsolved cases. Abbreviations: ATPase, adenosine triphosphatase; CK, creatine kinase; COX, cytochrome c oxidase; CT, computed tomography; GAPDH, glyceraldehyde-3-phosphate dehydrogenase; HGMD, human gene mutation database; MRC, Medical Research Council; NADH-TR, nicotinamide adenine dinucleotide dehydrogenase-tetrazolium reductase; NEB, nebulin gene; NGS, next generation sequencing; OMIM, online mendelian inheritance in man; PROVEAN, protein variation effect analyzer; SIFT, sorting intolerant from tolerant Key words: cores; core-rod myopathy; nebulin; nebulin expression; nemaline rods; next generation sequencing Correspondence to: D.-S. Kim; e-mail; [email protected] C 2015 Wiley Periodicals, Inc. V
Published online 12 November 2015 in Wiley Online Library (wileyonlinelibrary. com). DOI 10.1002/mus.24966
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NEB mutations are mainly found in autosomal recessive nemaline myopathies, which usually present in typical congenital forms, but clinical severities vary from lethal neonatal-onset to mild adult-onset phenotypes.4,5 Recessive NEB mutations may also cause distal myopathies with or without nemaline rods in muscles.6,7 Another congenital myopathy with distinct pathological features of nemaline rods and cores has also been reported to be associated with NEB mutations in 2 patients, both of whom presented with progressive muscle weakness and respiratory insufficiency.3,8 This type of congenital myopathy, socalled “rod and core myopathy”, is also known to be associated with mutations of other genes, including ACTA1, CFL2, RYR1, KBTBD13, and TPM2.9–13 In our cases of distal myopathy with core-rod pathology, we successfully detected novel NEB mutations by whole exome sequencing. We describe in detail their clinical and pathological features and describe the patterns of protein expression affected by these mutations. This report expands the spectrum of phenotypes and histopathologies of NEB-associated myopathies. PATIENTS AND METHODS Patients. Two patients
were included in this report based on their clinical features and the presence of nemaline rods and cores in their muscle biopsies. Informed consent was obtained from 1 patient and from the parents of the other. This study was approved by the ethical review board of Pusan National University Hospital. Patient 1. A 43-year-old man presented with ankle weakness of 5 years duration. An elder brother was similarly affected. The patient had delayed motor developmental milestones and was unable to match his peers during athletic activities during school years. On presentation, ankle dorsiflexion and plantarflexion were graded as 2/5, and thigh and upper arm muscles were graded 4 to 5-/5 on the Medical Research Council (MRC) scale. Asymmetrical calf atrophy was noted. Ankle MUSCLE & NERVE
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FIGURE 1. Muscle CT scans. (A) In lower legs of patient 1, gastrocnemius and soleus were most involved (arrows); anterior tibial muscles were less affected. (B) Posterior thigh muscles in patient 1 were partially atrophied (arrows). (C) In the lower leg muscles of patient 2, gastrocnemius and soleus were mildly affected (arrows). (D) Thigh muscles in patient 2 were relatively spared.
contractures were prominent, but no other skeletal deformity, such as scoliosis, was observed. His cheek muscles were mildly affected, but extraocular movement was full without ptosis. A higharched palate was not noted. Tendon stretch reflexes were absent in all limbs. Serum creatine kinase (CK) was within normal limits (103 IU/L, normal A (p.Ser8193Ser) was shared by both patients and has been reported previously in a patient with the typical Sequencing.
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FIGURE 2. Muscle pathology. (A) In patient 1, areas with deficient oxidative enzyme activity were frequently found on NADH stain. (B) In some fibers, multicores were present mimicking a moth-eaten appearance on NADH stain. (C) Rod structures were scattered within muscle fibers on modified Gomori-trichrome stain in patient 1. (D) In patient 1, a few ragged red fibers were observed on modified Gomori-trichrome. (E,F) In patient 2, core regions with deficient NADH and COX enzyme activities were found in smaller-sized type 1 fibers. (G) Most rod structures were scattered through the sarcoplasm, and some were clustered in subsarcolemmal regions (arrow) on modified Gomori-trichrome stain. (H) In patient 2, type 1 fibers were predominant and were much smaller than type 2 fibers on NADH stain. (I) Areas with mitochondrial loss and disrupted myofibrillar arrangement (arrows) were found on electron microscopy, which corresponded to core regions. (J) Materials with electron density similar to the Z-disk correlated with rod structures. Scale bar 5 50 lm in A–G; 100 lm in H; 1 lm in I–J.
congenital phenotype of nemaline myopathy.14 The same NEB mutations identified in patient 1 were also detected from his affected brother by targeted sequencing. Parents of the patients were not examined due to death or divorce. Nebulin Expression. Western blotting using antibodies targeting N-terminal and C-terminal epitopes of nebulin detected less protein in either patient than in normal controls (Fig. 3). Standardized immunoreactivity against nebulin was 22.3% and 13.1% of normal control levels for the Nterminal epitope, and 40.4% and 31.6% for the Cterminal in patients 1 and 2, respectively. DISCUSSION
Core-rod myopathy refers to a group of congenital myopathies in which cores and nemaline rods co-exist in muscle fibers. Although first reported in 482
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patients with RYR1 mutations, core-rod myopathy has also been reported in association with NEB, KBTBD13 (a member of the BTB/Kelch family), and TPM2 mutations.8–10 Before the reports of these genes as causative of core-rod myopathy, an ACTA1 mutation was reported to cause nemaline myopathy with cores, in which the core-like areas with unevenness of oxidative enzymes, as well as the presence of nemaline rods, were represented.12 Also, recessive mutations in CFL2, the gene encoding cofilin-2 and a causative gene for nemaline myopathy type 6, have also been described to display focal loss of oxidative enzymes consistent with minicores.13 The pathological patterns of cores and rods in the disease appear to be variable and are probably partly dependent on the causative genes. Although nemaline rods in patients with RYR1 mutations are seen in various ways, cores are centrally located and well demarcated, as is seen in MUSCLE & NERVE
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FIGURE 3. Nebulin expression by western blot analysis. (Left) Both antibodies targeting N-terminal and C-terminal epitopes of nebulin detected residual nebulin amounts in patients 1 and 2. (Right) Residual nebulin levels standardized against GAPDH were significant in amount but much reduced as compared with a normal subject.
central core disease.9 Two previous reports describing muscle pathology in NEB-related core-rod myopathy described well-demarcated cores and clustered rods in subsarcolemmal regions.3,8 On the other hand, KBTBD13- and TPM2-related disease show a different pathology, that is, nemaline rods are scattered through the sarcoplasm, and cores or minicores are randomly located with lack of clear demarcation.10,11 We find this difference remarkable, because in our patients, the muscle pathology resembled those of KBTBD13- and TPM2-related disease rather than previously reported cases with NEB mutations. Patient 1 also showed additional pathologic abnormality, that is, severely disorganized intermyofibrillar networks with a moth-eaten appearance and the presence of ragged red fibers containing mitochondrial crystalline inclusions. However, the significance of these observations is unclear. Thus, our series demonstrates that the pathological features of NEB-related core-rod myopathy are quite heterogeneous. The muscle images of various congenital myopathies show specific patterns of muscle involvement and often provide important clues regarding the identities of causative genes. To date, congenital myopathies caused by NEB mutations, such as nemaline myopathy and distal nebulin myopathy, usually show early involvement of anterior tibial muscles with relative preservation of gastrocnemius muscle until later stages.6,15 Previously described patients with NEB-related core-rod myopathy have exhibited similar patterns, that is, prominent involvement of the anterior compartment of distal legs and axial muscles with selective preservation of gastrocnemius muscle.3,8 However, in both of our patients, medial gastrocnemius and soleus were most severely affected, while anterior tibial muscles were partially involved in patient 1 but completely spared in patient 2. Furthermore, predominant and early involvement of gastrocnemius seems to be unusual for NEB-related myopathies. Median Nerve Penetration in CTS
On the other hand, asymmetrical muscle atrophy observed in patient 1 and his sibling is not uncommon in NEB-related myopathies.6 The very mild phenotype observed in our patients was also surprising, because previous cases of NEB-related core-rod myopathy have invariably had a severe phenotype. One patient presented with respiratory failure at birth (intermediate course), and another developed early respiratory insufficiency requiring ventilator support (typical congenital type).3,8 In another report of 6 patients with NEB-related core-rod myopathy, 2 were severe and 3 were typical congenital types.16 Although our patient 1 experienced delayed motor milestones in infancy, both patients maintained independent ambulation without definite progression during follow-up, and neither developed respiratory distress. Core-rod myopathies associated with RYR1, KBTBD13, or TPM2 are dominantly inherited and generally cause mild disease with normal respiratory function and prolonged independent ambulation, although a lethal case has been described.17 The correlation between residual nebulin amounts and clinical severity in NEB-related myopathies has been discussed in several reports.6,7,18 In a case of nemaline myopathy, compound heterozygosity for a frameshift mutation and a splice site mutation (intron 13) caused a marked reduction in nebulin amount and resulted in a more severe phenotype than homozygous exon 55 deletions.19 The above-mentioned findings suggest clinical severity might be influenced by residual nebulin, which is probably determined by mutation type. Both of our patients were compound heterozygous for a frameshift mutation and a splice site mutation. Two frameshift mutations in each allele are expected to produce truncated proteins that would subsequently be degraded. Accordingly, the majority of residual protein detected by western blot was probably due to another allele carrying p.Ser8193Ser, because splice site mutations are often leaky and may MUSCLE & NERVE
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produce normal transcripts. Thus, the milder phenotypes shown in our patients could be explained by greater amounts of residual nebulin. However, the presence a splice site mutation has not always correlated with higher nebulin amount and milder phenotype as shown in some other cases.14,20 In addition, the patients with a homozygous exon 55 deletion frequently show typical congenital or intermediate disease despite higher nebulin levels.21 Considering that patient 1 with a nebulin level similar to that of patients with homozygous exon 55 deletions17 had a much milder phenotype, we hypothesize that clinical severity is not likely to be only affected by residual nebulin amount, and that it is also determined by other unknown factors. Mutation searches for congenital myopathies are a challenging task except for a few subgroups which are associated with a few small-sized causative genes or have mutational hot spots. In this regard, recent development of NGS technology is expected to make a significant contribution to the research in this field. NGS has already had a strong impact on identifying new causative genes in many familial cases and has nearly replaced traditional linkage analysis. However, its use is still limited when analyzing single cases, mainly because of too many variants identified and difficulties in proving pathogenicity of individual variants. And thus, it is still advisable to use NGS with traditional Sanger sequencing of target genes in every case. In core-rod myopathy, diverse clinical features and marked genetic heterogeneity made it difficult to target a specific causative gene, and use of whole exome sequencing in combination with Sanger sequencing of a few target genes brought us successful results. In conclusion, we describe 2 patients with NEBrelated core-rod myopathy, who have a very mild phenotype and unusual pathologic features of rods and cores. This study shows that core-rod myopathy is a genetically heterogeneous entity with variable clinical and pathological findings, even among those with NEB mutations. Our findings indicate that the residual nebulin amount is partly related to clinical phenotype severity. Further studies are required to further our understanding of the pathomechanism affecting clinical and pathological manifestations in NEB-related core-rod myopathy. This study was supported by a Biomedical Research Institute Grant (2012-05), Pusan National University Hospital. The authors have no financial relationship or potential conflict of interest to declare.
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REFERENCES 1. Donner K, Sandbacka M, Lehtokari VL, Wallgren-Pettersson C, Pelin K. Complete genomic structure of the human nebulin gene and identification of alternatively spliced transcripts. Eur J Hum Genet 2004;12:744–751. 2. Ottenheijm CA, Granzier H, Labeit S. The sarcomeric protein nebulin: another multifunctional giant in charge of muscle strength optimization. Front Physiol 2012;3:37. 3. Scoto M, Cullup T, Cirak S, Yau S, Manzur AY, Feng L, et al. Nebulin (NEB) mutations in a childhood onset distal myopathy with rods and cores uncovered by next generation sequencing. Eur J Hum Genet 2013;21:1249–1252. 4. Wallgren-Pettersson C, Donner K, Sewry C, Bijlsma E, Lammens M, Bushby K, et al. Mutations in the nebulin gene can cause severe congenital nemaline myopathy. Neuromuscul Disord 2002;12:674–679. 5. Wallgren-Pettersson C, Pelin K, Nowak KJ, Muntoni F, Romero NB, Goebel HH, et al. Genotype-phenotype correlations in nemaline myopathy caused by mutations in the genes for nebulin and skeletal muscle alpha-actin. Neuromuscul Disord 2004;14:461–470. 6. Wallgren-Pettersson C, Lehtokari VL, Kalimo H, Paetau A, Nuutin E, Hackman P, et al. Distal myopathy caused by homozygous missense mutations in the nebulin gene. Brain 2007;130:1465–1476. 7. Lehtokari VL, Pelin K, Herczegfalvi A, Karcagi V, Pouget J, Franques J, et al. Nemaline myopathy caused by mutations in the nebulin gene may present as a distal myopathy. Neuromuscul Disord 2011;21:556– 562. 8. Romero NB, Lehtokari VL, Quijano-Roy S, Monnier N, Claeys KG, Carlier RY, et al. Core-rod myopathy caused by mutations in the nebulin gene. Neurology 2009;73:1159–1161. 9. Monnier N, Romero NB, Lerale J, Nivoche Y, Qi D, Mac Lennan DH, et al. An autosomal dominant congenital myopathy with cores and rods is associated with a neomutation in the RYR1 gene encoding the skeletal muscle ryanodine receptor. Hum Mol Genet 2000;9: 2599–2608. 10. Sambuughin N, Yau KS, Oliv e M, Duff RM, Bayarsaikhan M, Lu S, et al. Dominant mutations in KBTBD13, a member of the BTB/Kelch family, cause nemaline myopathy with cores. Am J Hum Genet 2010; 87:842–847. 11. Davidson AE, Siddiqui FM, Lopez MA, Lunt P, Carlson HA, Moore BE, et al. Novel deletion of lysine 7 expands the clinical, histopathological and genetic spectrum of TPM2-related myopathies. Brain 2013;136:508–521. 12. Jungbluth H, Sewry CA, Brown SC, Nowak KJ, Laing NG, WallgrenPettersson C, et al. Mild phenotype of nemaline myopathy with sleep hypoventilation due to a mutation in the skeletal muscle alpha-actin (ACTA1) gene. Neuromuscul Disord 2001;11:35–40. 13. Agrawal PB, Greenleaf RS, Tomczak KK, Lehtokari VL, WallgrenPettersson C, Wallefeld W, et al. Nemaline myopathy with minicores caused by mutation of the CFL2 gene encoding the skeletal muscle actin-binding protein, cofilin-2. Am J Hum Genet 2007;80:162–167. 14. Malfatti E, Lehtokari VL, B€ ohm J, de Winter JM, Schaffer U, Estournet B, et al. Muscle histopathology in nebulin-related nemaline myopathy: ultrastrastructural findings correlated to disease severity and genotype. Acta Neuropathol Commun 2014;2:44. 15. Jungbluth H, Sewry CA, Counsell S, AllsopJ, Chattopadhyay A, Mercuri E, et al. Magnetic resonance imaging of muscle in nemaline myopathy. Neuromuscul Disord 2004;14:779–784. 16. Lehtokari VL, Kiiski K, Sandaradura SA, Laporte J, Repo P. Frey JA, et al. Mutation update: the spectra of nebulin variants and associated myopathies. Hum Mutat 2014;35:1418–1426. 17. Hernandez-Lain A, Husson I, Monnier N, Farnoux C, Brochier G, Lacene E, et al. De novo RYR1 heterozygous mutation (I4898T) causing lethal core-rod myopathy in twins. Eur J Med Genet 2011;54: 29–33. 18. Ottenheijm CA, Hooijman P, DeChene ET, Stienen GJ, Beggs AH, Granzier H. Altered myofilament function depresses force generation in patients with nebulin-based nemaline myopathy (NEM2). J Struct Biol 2010;170:334–343. 19. Lawlor MW, Ottenheijm CA, Lehtokari VL, Cho K, Pelin K, Wallgren-Pettersson C, et al. Novel mutations in NEB cause abnormal nebulin expression and markedly impaired muscle force generation in severe nemaline myopathy. Skelet Muscle 2011;1:23. 20. de Winter JM, Buck D, Hidalgo C, Jasper JR, Malik FI, Clarke NF, et al. Troponin activator augments muscle force in nemaline myopathy patients with nebulin mutations. J Med Genet 2013;50:383–392. 21. Lehtokari VL, Greenleaf RS, DeChene ET, Kellinsalmi M, Pelin K, Laing NG, et al. The exon 55 deletion in the nebulin gene--one single founder mutation with world-wide occurrence. Neuromuscul Disord 2009;19:179–181.
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MEDIAN NERVE PENETRATION BY A PERSISTENT MEDIAN ARTERY AND VEIN MIMICKING CARPAL TUNNEL SYNDROME KARA STAVROS, MD,1 DAVID PAIK, MD,2 RAJEEV MOTIWALA, MD,3 JESSE WEINBERGER, MD,3 LAN ZHOU, MD,3 and SUSAN SHIN, MD3 1
Department of Neurology, Warren Alpert Medical School of Brown University, Providence, Rhode island, USA Department of Radiology, Morristown Medical Center, Morristown, New Jersey, USA 3 Department of Neurology, Icahn School of Medicine at Mount Sinai, 1468 Madison Avenue, Annenberg Second Floor, Box 1052, New York, New York, 10029, USA 2
Accepted 11 November 2015 ABSTRACT: Introduction: Carpal tunnel syndrome (CTS) is a common clinical syndrome seen in the outpatient setting that is easily confirmed by electrodiagnostic testing. Methods: We describe the case of a patient who presented with the classic symptoms and neurological examination for CTS, but had a normal nerve conduction study and electromyogram. Results: Neuromuscular ultrasound of the median nerve on the symptomatic side revealed penetration of the nerve by a persistent median artery and vein in the mid-forearm, with a positive sonographic Tinel sign over this spot. This finding is an anatomical variation that has been described sparingly in the literature, mostly in cadavers. It has not been reported previously to be a mimic of CTS. Conclusions: This case demonstrates the diagnostic utility of neuromuscular ultrasound and the importance of considering an anatomical variation involving the median nerve in the differential diagnosis of CTS. Muscle Nerve 53:485–487, 2016
Carpal tunnel syndrome (CTS) is commonly encountered in the neurology clinic, and the diagnosis can be readily confirmed with nerve conduction study and electromyography. We describe the case of a patient who presented with classic history and neurological examination findings for CTS but had normal electrodiagnostic testing. Neuromuscular ultrasound done to search for a structural cause of the symptoms revealed an unusual anatomical variation proximal to the carpal tunnel, which resulted in a CTS mimic. CASE REPORT
A 47-year-old, right-handed man presented for evaluation of several years of left hand pain and paresthesias. Symptoms began as intermittent numbness and tingling in the left hand and progressed to become more constant and severe in the last year. The pain often woke him from
Additional Supporting Information may be found in the online version of this article. Abbreviations: AVM, arteriovenous malformation; CTS, carpal tunnel syndrome; CSA, cross-sectional area; PMA, persistent median artery; PMV, persistent median vein Key words: carpal tunnel syndrome; median nerve penetration; median neuropathy; neuromuscular ultrasound; persistent median artery Correspondence to: S. Shin; e-mail: [email protected] C 2015 Wiley Periodicals, Inc. V
Published online 13 November 2015 in Wiley Online Library (wileyonlinelibrary. com). DOI 10.1002/mus.24974
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sleep. Most of the paresthesias were localized to left digits 1–3. He did not have any neck pain, weakness, or any symptoms in the right hand. Neurological examination revealed normal strength and muscle bulk. Reflexes were 21 in all limbs. Sensation was diminished to pinprick in the left median nerve distribution, sparing the thenar eminence in the distribution of the palmar cutaneous branch of the median nerve. Otherwise, sensation was intact to all modalities in all extremities. Tinel and Phalen signs were not present at the wrist. Nerve conduction study showed no signs of a median neuropathy with normal left and right median nerve distal motor latencies and sensory nerve conduction studies (Table 1). Short segment incremental motor nerve conduction studies across the wrist were also normal. Electromyography of median-innervated muscles showed no abnormalities. Subsequently, diagnostic neuromuscular ultrasound of the left median nerve was performed in real time using a linear-array transducer (15L4; Terason, Burlington, Massachusetts). The median nerve cross-sectional area (CSA) was measured using a trace method done inside the hyperechoic epineurium. The left median nerve at the wrist had a normal, non-bifid appearance, with the exception of the presence of a persistent median artery and vein (Fig. 1A). The 2 vessels were distinguished by the compressibility of the vein and by the minimal compressibility and pulsatile, unidirectional flow of the artery. The CSA of the median nerve without the vascular structures at the wrist was measured to be 9 mm2. Ultrasound examination of the nerve approximately 6 cm proximal to the distal wrist crease revealed a focal region of enlargement of the nerve (CSA 16 mm2) (Fig. 1B); this was noted just distal to the site of penetration of the median nerve by the persistent median artery and vein. There was reunification of the separated nerve fibers immediately distal to the penetration site (Fig. 1; see also Video 1 in the Supplementary Material, available online). Pressure to this area from the ultrasound probe produced prominent paresthesias consistent with a sonographic Tinel MUSCLE & NERVE
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Table 1. Motor and sensory nerve conduction studies of the left median nerve.* Nerve and site
Distallatency (ms)
Amplitude (mV)
Conductionvelocity (m/s)
Left median motor NCS Wrist 3.5 7.8 Elbow 7.9 6.6 Left median sensory NCS Wrist 2.2 48 Left mixed palmar median and ulnar sensory NCS Palmar (median) 1.5 66 Palmar (ulnar) 1.6 29
— 55 60 59 55
NCS, nerve conduction study. *All values are within normal ranges.
sign. The contralateral median nerve was normal with a CSA of 9 mm2 at the wrist and mid-forearm. Subsequent MRI reported the presence of a persistent median artery, but it did not show the penetration of the nerve. The patient was started on gabapentin for neuropathic pain with nearcomplete resolution of his symptoms. Surgical exploration was not considered, as this finding is a normal anatomical variant, and the patient’s symptoms were well-controlled with gabapentin. DISCUSSION
This patient presented with symptoms and clinical examination that are classic for entrapment of the median nerve at the wrist. However nerve con-
duction study and electromyography failed to confirm this diagnosis. In addition, the prominent unilaterality of symptoms in his non-dominant hand is unusual for CTS. Further evaluation with neuromuscular ultrasound revealed the true pathology, consisting of penetration of the left median nerve by a persistent median artery and vein in the mid-forearm as the cause for the symptoms. The median artery provides blood supply to the hand in the developing fetus and typically regresses after the second month of gestation as the ulnar and radial arteries develop. The presence of a persistent median artery is not uncommon, with prevalence ranging from 4% to 16%.1 However, penetration of the median nerve by a persistent median artery is not widely reported. There have been several demonstrations of this anatomical variant in cadavers,1–3 and there have been 2 reports in living patients. In 1 case, the variant was discovered when the patient underwent ultrasound-guided median nerve block for median neuropathy,4 but the details of the clinical history and examination are not known. In the other case, the variant was discovered upon surgical exploration for suspected pronator teres syndrome.5 There has also been a report of an arteriovenous malformation (AVM) of a persistent median artery in a young boy with symptoms consistent with CTS in which the nerve bifurcated at the level of the AVM and did not
FIGURE 1. (A–F) Gray-scale ultrasound images of the left median nerve showing bisection by a persistent median artery (PMA) and vein (PMV). (A) Normal-appearing median nerve at the wrist along with a PMA and PMV. (B) Measurement approximately 6 cm proximal to the distal wrist crease shows the point of maximal enlargement of the nerve. Subsequent images are distal to proximal in sequence. For further detail, see Video 1 (see Supplementary Material, available online) which shows imaging of gray-scale ultrasound of the left median nerve bisected by the persistent median artery and vein. 486
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rejoin distally.6 There are other rare reports of structural compromise of the median nerve by other blood vessels, including the brachial artery,7 subscapular artery,8 and posterior circumflex humeral artery.8 All of these findings were seen in cadavers. Neuromuscular ultrasound has been proposed as a complement to electrodiagnostic studies for CTS and other peripheral neuropathies.9,10 By itself, there is strong evidence that neuromuscular ultrasound measurement of median nerve CSA at the wrist is an accurate test for the diagnosis of CTS.9 In addition, a recent study showed that, in about 50% of patients with a clinical diagnosis of CTS and normal nerve conduction studies, neuromuscular ultrasound was abnormal and confirmed the clinical diagnosis.11 When compared with conventional nerve conduction studies, neuromuscular ultrasound is superior for identification of anatomical variations that may be of particular importance to a surgeon, such as a bifid median nerve or persistent median artery, as well as pathological findings, such as cysts or neuromas.9 It is difficult to compare directly the sensitivity of neuromuscular ultrasound and electrodiagnostic studies for the diagnosis of CTS as most studies have used electrodiagnostic studies as the “gold standard.” Comparison of neuromuscular ultrasound with MRI for median neuropathy suggests that ultrasound has greater sensitivity and is more cost-efficient.12 This is consistent with the case described in this study, where the ultimate diagnosis was made by neuromuscular ultrasound and was not well visualized on MRI. In addition, in a recent study of ultrasound versus MRI for other focal peripheral neuropathies excluding CTS, ultrasound was also found to be more sensitive than MRI and with comparable specificity. Thus, ultrasound may be the preferred imaging modality for peripheral neuropathies.13
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The case described is an interesting example of the median nerve being penetrated by a persistent median artery and vein with rejoining of the nerve fibers into a single nerve immediately distal to the site of penetration. It demonstrates the importance of considering anatomical variations in the investigation of symptoms that are suggestive of the more common entity of CTS, but with inconsistent electrodiagnostic test results. These variants are especially important to consider in patients referred for surgery to avoid unnecessary intervention or inadvertent nerve injury. We have also highlighted the great diagnostic utility of neuromuscular ultrasound in the evaluation of these cases of structural anomalies, which may go unseen by conventional nerve conduction study, electromyography, or MRI. REFERENCES 1. Singla RK, Kaur N, Dhiraj GS. Prevalence of the persistent median artery. J Clin Diagn Res 2012;6:1454–1457. 2. Srivastava SK, Pande BS. Anomalous pattern of median artery in the forearm of Indians. Acta Anat (Basel) 1990;138:193–194. 3. Sanudo JR, Chikwe J, Evans SE. Anomalous median nerve associated with a persistent median artery. J Anat 1994;185:447–451. 4. Dolan J, Milligan P. Persistent median artery and veins in patients undergoing elective day case hand surgery. Reg Anesth Pain Med 2013;38:462–463. 5. Jones NF, Ming NL. Persistent median artery as a cause of pronator syndrome. J Hand Surg 1988;13:728–732. 6. Gutowski KA, Olivier WA, Mehrara BJ, Friedman DW. Arteriovenous malformation of a persistent median artery with a bifurcated median nerve. Plast Reconstr Surg 2000;106:1336–1339. 7. Roy TS. Median nerve penetration by a muscular branch of the brachial artery. Clin Anat 2003;16:335–339. 8. Miller RA. Observations upon the arrangement of the axillary artery and brachial plexus. Am J Anat 1939;64:143–163. 9. Cartwright MS, Hobson-Webb LD, Boon AJ, Alter KE, Hunt CH, Flores VH, et al. Evidence-based guideline: neuromuscular ultrasound for the diagnosis of carpal tunnel syndrome. Muscle Nerve 2012;46: 287–293. 10. Walker FO, Cartwright MS, Wiesler ER, Caress J. Ultrasound of nerve and muscle. Clin Neurophysiol 2004;115:495–507. 11. Al-Hashel JY, Rashad HM, Nouh MR, Amro HA, Khuraibet AJ, Shamov T, et al. Sonography in carpal tunnel syndrome with normal nerve conduction studies. Muscle Nerve 2015;51:592–597. 12. Deniz FE, Okusz E, Sarikaya B, Kurt S, Erkorkmaz U, Ulusoy H, et al. Comparison of the diagnostic utility of electromyography, ultrasonography, computed tomography, and magnetic resonance imaging in idiopathic carpal tunnel syndrome determined by clinical findings. Neurosurgery 2012;70:610–616. 13. Zaidman CM, Seelig MJ, Baker JC, Mackinnon SE, Pestronk A. Detection of peripheral nerve pathology. Neurology 2013;80:1634–1640.
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NEB-RELATED CORE-ROD MYOPATHY WITH DISTINCT CLINICAL AND PATHOLOGICAL FEATURES YOUNG-EUN PARK, MD, PHD,1,2 JIN-HONG SHIN, MD, PhD,1,3 BORAM KANG, MS,3 CHANG-HOON LEE, MD, PhD,2,4 and DAE-SEONG KIM, MD, PhD1,3 1
Department of Neurology, Pusan National University Yangsan Hospital, Beomo-ri, Mulgeum-eup, Yangsan, 626-770 Gyeongnam, South Korea 2 Biomedical Research Institute, Pusan National University Hospital, Busan, South Korea 3 Research Institute for Convergence of Biomedical Research and Technology, Pusan National University Yangsan Hospital, Gyeongnam, South Korea 4 Department of Pathology, Pusan National University, Busan, South Korea Accepted 2 November 2015 ABSTRACT: Introduction: Mutations in the gene encoding nebulin (NEB) are known to cause several types of congenital myopathy including recessive nemaline myopathy and distal nebulin myopathy. Core-rod myopathy has recently been reported to be another type of NEB-related myopathy, and is pathologically characterized by the coexistence of cores and nemaline rods within muscle fibers. Methods: We describe 2 patients with core-rod myopathy who were analyzed genetically by whole exome sequencing and evaluated clinically and pathologically. Findings were compared with those of patients with the disease of other genetic causes. Results: Three NEB mutations were identified, 2 of which were novel. Mild clinical features, unusual patterns of muscle involvement, and atypical pathological findings were observed. Conclusions: We propose that the clinical and pathological spectrum of core-rod myopathy should be widened. A significant amount of residual nebulin expression is believed to contribute to the much milder phenotype exhibited by the patients we describe here. Muscle Nerve 53:479–484, 2016
Nebulin is one of the giant proteins in sarcomeres. It spans the whole length of thin filaments and binds more than 200 actin monomers. In addition to maintaining the lengths of thin filaments, it is involved in cross-bridge cycling kinetics and in regulation of calcium sensitivity.1,2 Although mutations in the nebulin gene (NEB) have long been implicated in congenital myopathies, sequencing of NEB has been a challenge due to its huge size and the repetitive nature of its sequence.3 The recent advent of next generation sequencing (NGS) technology has facilitated access to large muscle genes like NEB and enabled interrogation of otherwise unsolved cases. Abbreviations: ATPase, adenosine triphosphatase; CK, creatine kinase; COX, cytochrome c oxidase; CT, computed tomography; GAPDH, glyceraldehyde-3-phosphate dehydrogenase; HGMD, human gene mutation database; MRC, Medical Research Council; NADH-TR, nicotinamide adenine dinucleotide dehydrogenase-tetrazolium reductase; NEB, nebulin gene; NGS, next generation sequencing; OMIM, online mendelian inheritance in man; PROVEAN, protein variation effect analyzer; SIFT, sorting intolerant from tolerant Key words: cores; core-rod myopathy; nebulin; nebulin expression; nemaline rods; next generation sequencing Correspondence to: D.-S. Kim; e-mail; [email protected] C 2015 Wiley Periodicals, Inc. V
Published online 12 November 2015 in Wiley Online Library (wileyonlinelibrary. com). DOI 10.1002/mus.24966
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NEB mutations are mainly found in autosomal recessive nemaline myopathies, which usually present in typical congenital forms, but clinical severities vary from lethal neonatal-onset to mild adult-onset phenotypes.4,5 Recessive NEB mutations may also cause distal myopathies with or without nemaline rods in muscles.6,7 Another congenital myopathy with distinct pathological features of nemaline rods and cores has also been reported to be associated with NEB mutations in 2 patients, both of whom presented with progressive muscle weakness and respiratory insufficiency.3,8 This type of congenital myopathy, socalled “rod and core myopathy”, is also known to be associated with mutations of other genes, including ACTA1, CFL2, RYR1, KBTBD13, and TPM2.9–13 In our cases of distal myopathy with core-rod pathology, we successfully detected novel NEB mutations by whole exome sequencing. We describe in detail their clinical and pathological features and describe the patterns of protein expression affected by these mutations. This report expands the spectrum of phenotypes and histopathologies of NEB-associated myopathies. PATIENTS AND METHODS Patients. Two patients
were included in this report based on their clinical features and the presence of nemaline rods and cores in their muscle biopsies. Informed consent was obtained from 1 patient and from the parents of the other. This study was approved by the ethical review board of Pusan National University Hospital. Patient 1. A 43-year-old man presented with ankle weakness of 5 years duration. An elder brother was similarly affected. The patient had delayed motor developmental milestones and was unable to match his peers during athletic activities during school years. On presentation, ankle dorsiflexion and plantarflexion were graded as 2/5, and thigh and upper arm muscles were graded 4 to 5-/5 on the Medical Research Council (MRC) scale. Asymmetrical calf atrophy was noted. Ankle MUSCLE & NERVE
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FIGURE 1. Muscle CT scans. (A) In lower legs of patient 1, gastrocnemius and soleus were most involved (arrows); anterior tibial muscles were less affected. (B) Posterior thigh muscles in patient 1 were partially atrophied (arrows). (C) In the lower leg muscles of patient 2, gastrocnemius and soleus were mildly affected (arrows). (D) Thigh muscles in patient 2 were relatively spared.
contractures were prominent, but no other skeletal deformity, such as scoliosis, was observed. His cheek muscles were mildly affected, but extraocular movement was full without ptosis. A higharched palate was not noted. Tendon stretch reflexes were absent in all limbs. Serum creatine kinase (CK) was within normal limits (103 IU/L, normal A (p.Ser8193Ser) was shared by both patients and has been reported previously in a patient with the typical Sequencing.
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FIGURE 2. Muscle pathology. (A) In patient 1, areas with deficient oxidative enzyme activity were frequently found on NADH stain. (B) In some fibers, multicores were present mimicking a moth-eaten appearance on NADH stain. (C) Rod structures were scattered within muscle fibers on modified Gomori-trichrome stain in patient 1. (D) In patient 1, a few ragged red fibers were observed on modified Gomori-trichrome. (E,F) In patient 2, core regions with deficient NADH and COX enzyme activities were found in smaller-sized type 1 fibers. (G) Most rod structures were scattered through the sarcoplasm, and some were clustered in subsarcolemmal regions (arrow) on modified Gomori-trichrome stain. (H) In patient 2, type 1 fibers were predominant and were much smaller than type 2 fibers on NADH stain. (I) Areas with mitochondrial loss and disrupted myofibrillar arrangement (arrows) were found on electron microscopy, which corresponded to core regions. (J) Materials with electron density similar to the Z-disk correlated with rod structures. Scale bar 5 50 lm in A–G; 100 lm in H; 1 lm in I–J.
congenital phenotype of nemaline myopathy.14 The same NEB mutations identified in patient 1 were also detected from his affected brother by targeted sequencing. Parents of the patients were not examined due to death or divorce. Nebulin Expression. Western blotting using antibodies targeting N-terminal and C-terminal epitopes of nebulin detected less protein in either patient than in normal controls (Fig. 3). Standardized immunoreactivity against nebulin was 22.3% and 13.1% of normal control levels for the Nterminal epitope, and 40.4% and 31.6% for the Cterminal in patients 1 and 2, respectively. DISCUSSION
Core-rod myopathy refers to a group of congenital myopathies in which cores and nemaline rods co-exist in muscle fibers. Although first reported in 482
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patients with RYR1 mutations, core-rod myopathy has also been reported in association with NEB, KBTBD13 (a member of the BTB/Kelch family), and TPM2 mutations.8–10 Before the reports of these genes as causative of core-rod myopathy, an ACTA1 mutation was reported to cause nemaline myopathy with cores, in which the core-like areas with unevenness of oxidative enzymes, as well as the presence of nemaline rods, were represented.12 Also, recessive mutations in CFL2, the gene encoding cofilin-2 and a causative gene for nemaline myopathy type 6, have also been described to display focal loss of oxidative enzymes consistent with minicores.13 The pathological patterns of cores and rods in the disease appear to be variable and are probably partly dependent on the causative genes. Although nemaline rods in patients with RYR1 mutations are seen in various ways, cores are centrally located and well demarcated, as is seen in MUSCLE & NERVE
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FIGURE 3. Nebulin expression by western blot analysis. (Left) Both antibodies targeting N-terminal and C-terminal epitopes of nebulin detected residual nebulin amounts in patients 1 and 2. (Right) Residual nebulin levels standardized against GAPDH were significant in amount but much reduced as compared with a normal subject.
central core disease.9 Two previous reports describing muscle pathology in NEB-related core-rod myopathy described well-demarcated cores and clustered rods in subsarcolemmal regions.3,8 On the other hand, KBTBD13- and TPM2-related disease show a different pathology, that is, nemaline rods are scattered through the sarcoplasm, and cores or minicores are randomly located with lack of clear demarcation.10,11 We find this difference remarkable, because in our patients, the muscle pathology resembled those of KBTBD13- and TPM2-related disease rather than previously reported cases with NEB mutations. Patient 1 also showed additional pathologic abnormality, that is, severely disorganized intermyofibrillar networks with a moth-eaten appearance and the presence of ragged red fibers containing mitochondrial crystalline inclusions. However, the significance of these observations is unclear. Thus, our series demonstrates that the pathological features of NEB-related core-rod myopathy are quite heterogeneous. The muscle images of various congenital myopathies show specific patterns of muscle involvement and often provide important clues regarding the identities of causative genes. To date, congenital myopathies caused by NEB mutations, such as nemaline myopathy and distal nebulin myopathy, usually show early involvement of anterior tibial muscles with relative preservation of gastrocnemius muscle until later stages.6,15 Previously described patients with NEB-related core-rod myopathy have exhibited similar patterns, that is, prominent involvement of the anterior compartment of distal legs and axial muscles with selective preservation of gastrocnemius muscle.3,8 However, in both of our patients, medial gastrocnemius and soleus were most severely affected, while anterior tibial muscles were partially involved in patient 1 but completely spared in patient 2. Furthermore, predominant and early involvement of gastrocnemius seems to be unusual for NEB-related myopathies. Median Nerve Penetration in CTS
On the other hand, asymmetrical muscle atrophy observed in patient 1 and his sibling is not uncommon in NEB-related myopathies.6 The very mild phenotype observed in our patients was also surprising, because previous cases of NEB-related core-rod myopathy have invariably had a severe phenotype. One patient presented with respiratory failure at birth (intermediate course), and another developed early respiratory insufficiency requiring ventilator support (typical congenital type).3,8 In another report of 6 patients with NEB-related core-rod myopathy, 2 were severe and 3 were typical congenital types.16 Although our patient 1 experienced delayed motor milestones in infancy, both patients maintained independent ambulation without definite progression during follow-up, and neither developed respiratory distress. Core-rod myopathies associated with RYR1, KBTBD13, or TPM2 are dominantly inherited and generally cause mild disease with normal respiratory function and prolonged independent ambulation, although a lethal case has been described.17 The correlation between residual nebulin amounts and clinical severity in NEB-related myopathies has been discussed in several reports.6,7,18 In a case of nemaline myopathy, compound heterozygosity for a frameshift mutation and a splice site mutation (intron 13) caused a marked reduction in nebulin amount and resulted in a more severe phenotype than homozygous exon 55 deletions.19 The above-mentioned findings suggest clinical severity might be influenced by residual nebulin, which is probably determined by mutation type. Both of our patients were compound heterozygous for a frameshift mutation and a splice site mutation. Two frameshift mutations in each allele are expected to produce truncated proteins that would subsequently be degraded. Accordingly, the majority of residual protein detected by western blot was probably due to another allele carrying p.Ser8193Ser, because splice site mutations are often leaky and may MUSCLE & NERVE
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produce normal transcripts. Thus, the milder phenotypes shown in our patients could be explained by greater amounts of residual nebulin. However, the presence a splice site mutation has not always correlated with higher nebulin amount and milder phenotype as shown in some other cases.14,20 In addition, the patients with a homozygous exon 55 deletion frequently show typical congenital or intermediate disease despite higher nebulin levels.21 Considering that patient 1 with a nebulin level similar to that of patients with homozygous exon 55 deletions17 had a much milder phenotype, we hypothesize that clinical severity is not likely to be only affected by residual nebulin amount, and that it is also determined by other unknown factors. Mutation searches for congenital myopathies are a challenging task except for a few subgroups which are associated with a few small-sized causative genes or have mutational hot spots. In this regard, recent development of NGS technology is expected to make a significant contribution to the research in this field. NGS has already had a strong impact on identifying new causative genes in many familial cases and has nearly replaced traditional linkage analysis. However, its use is still limited when analyzing single cases, mainly because of too many variants identified and difficulties in proving pathogenicity of individual variants. And thus, it is still advisable to use NGS with traditional Sanger sequencing of target genes in every case. In core-rod myopathy, diverse clinical features and marked genetic heterogeneity made it difficult to target a specific causative gene, and use of whole exome sequencing in combination with Sanger sequencing of a few target genes brought us successful results. In conclusion, we describe 2 patients with NEBrelated core-rod myopathy, who have a very mild phenotype and unusual pathologic features of rods and cores. This study shows that core-rod myopathy is a genetically heterogeneous entity with variable clinical and pathological findings, even among those with NEB mutations. Our findings indicate that the residual nebulin amount is partly related to clinical phenotype severity. Further studies are required to further our understanding of the pathomechanism affecting clinical and pathological manifestations in NEB-related core-rod myopathy. This study was supported by a Biomedical Research Institute Grant (2012-05), Pusan National University Hospital. The authors have no financial relationship or potential conflict of interest to declare.
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REFERENCES 1. Donner K, Sandbacka M, Lehtokari VL, Wallgren-Pettersson C, Pelin K. Complete genomic structure of the human nebulin gene and identification of alternatively spliced transcripts. Eur J Hum Genet 2004;12:744–751. 2. Ottenheijm CA, Granzier H, Labeit S. The sarcomeric protein nebulin: another multifunctional giant in charge of muscle strength optimization. Front Physiol 2012;3:37. 3. Scoto M, Cullup T, Cirak S, Yau S, Manzur AY, Feng L, et al. Nebulin (NEB) mutations in a childhood onset distal myopathy with rods and cores uncovered by next generation sequencing. Eur J Hum Genet 2013;21:1249–1252. 4. Wallgren-Pettersson C, Donner K, Sewry C, Bijlsma E, Lammens M, Bushby K, et al. Mutations in the nebulin gene can cause severe congenital nemaline myopathy. Neuromuscul Disord 2002;12:674–679. 5. Wallgren-Pettersson C, Pelin K, Nowak KJ, Muntoni F, Romero NB, Goebel HH, et al. Genotype-phenotype correlations in nemaline myopathy caused by mutations in the genes for nebulin and skeletal muscle alpha-actin. Neuromuscul Disord 2004;14:461–470. 6. Wallgren-Pettersson C, Lehtokari VL, Kalimo H, Paetau A, Nuutin E, Hackman P, et al. Distal myopathy caused by homozygous missense mutations in the nebulin gene. Brain 2007;130:1465–1476. 7. Lehtokari VL, Pelin K, Herczegfalvi A, Karcagi V, Pouget J, Franques J, et al. Nemaline myopathy caused by mutations in the nebulin gene may present as a distal myopathy. Neuromuscul Disord 2011;21:556– 562. 8. Romero NB, Lehtokari VL, Quijano-Roy S, Monnier N, Claeys KG, Carlier RY, et al. Core-rod myopathy caused by mutations in the nebulin gene. Neurology 2009;73:1159–1161. 9. Monnier N, Romero NB, Lerale J, Nivoche Y, Qi D, Mac Lennan DH, et al. An autosomal dominant congenital myopathy with cores and rods is associated with a neomutation in the RYR1 gene encoding the skeletal muscle ryanodine receptor. Hum Mol Genet 2000;9: 2599–2608. 10. Sambuughin N, Yau KS, Oliv e M, Duff RM, Bayarsaikhan M, Lu S, et al. Dominant mutations in KBTBD13, a member of the BTB/Kelch family, cause nemaline myopathy with cores. Am J Hum Genet 2010; 87:842–847. 11. Davidson AE, Siddiqui FM, Lopez MA, Lunt P, Carlson HA, Moore BE, et al. Novel deletion of lysine 7 expands the clinical, histopathological and genetic spectrum of TPM2-related myopathies. Brain 2013;136:508–521. 12. Jungbluth H, Sewry CA, Brown SC, Nowak KJ, Laing NG, WallgrenPettersson C, et al. Mild phenotype of nemaline myopathy with sleep hypoventilation due to a mutation in the skeletal muscle alpha-actin (ACTA1) gene. Neuromuscul Disord 2001;11:35–40. 13. Agrawal PB, Greenleaf RS, Tomczak KK, Lehtokari VL, WallgrenPettersson C, Wallefeld W, et al. Nemaline myopathy with minicores caused by mutation of the CFL2 gene encoding the skeletal muscle actin-binding protein, cofilin-2. Am J Hum Genet 2007;80:162–167. 14. Malfatti E, Lehtokari VL, B€ ohm J, de Winter JM, Schaffer U, Estournet B, et al. Muscle histopathology in nebulin-related nemaline myopathy: ultrastrastructural findings correlated to disease severity and genotype. Acta Neuropathol Commun 2014;2:44. 15. Jungbluth H, Sewry CA, Counsell S, AllsopJ, Chattopadhyay A, Mercuri E, et al. Magnetic resonance imaging of muscle in nemaline myopathy. Neuromuscul Disord 2004;14:779–784. 16. Lehtokari VL, Kiiski K, Sandaradura SA, Laporte J, Repo P. Frey JA, et al. Mutation update: the spectra of nebulin variants and associated myopathies. Hum Mutat 2014;35:1418–1426. 17. Hernandez-Lain A, Husson I, Monnier N, Farnoux C, Brochier G, Lacene E, et al. De novo RYR1 heterozygous mutation (I4898T) causing lethal core-rod myopathy in twins. Eur J Med Genet 2011;54: 29–33. 18. Ottenheijm CA, Hooijman P, DeChene ET, Stienen GJ, Beggs AH, Granzier H. Altered myofilament function depresses force generation in patients with nebulin-based nemaline myopathy (NEM2). J Struct Biol 2010;170:334–343. 19. Lawlor MW, Ottenheijm CA, Lehtokari VL, Cho K, Pelin K, Wallgren-Pettersson C, et al. Novel mutations in NEB cause abnormal nebulin expression and markedly impaired muscle force generation in severe nemaline myopathy. Skelet Muscle 2011;1:23. 20. de Winter JM, Buck D, Hidalgo C, Jasper JR, Malik FI, Clarke NF, et al. Troponin activator augments muscle force in nemaline myopathy patients with nebulin mutations. J Med Genet 2013;50:383–392. 21. Lehtokari VL, Greenleaf RS, DeChene ET, Kellinsalmi M, Pelin K, Laing NG, et al. The exon 55 deletion in the nebulin gene--one single founder mutation with world-wide occurrence. Neuromuscul Disord 2009;19:179–181.
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MEDIAN NERVE PENETRATION BY A PERSISTENT MEDIAN ARTERY AND VEIN MIMICKING CARPAL TUNNEL SYNDROME KARA STAVROS, MD,1 DAVID PAIK, MD,2 RAJEEV MOTIWALA, MD,3 JESSE WEINBERGER, MD,3 LAN ZHOU, MD,3 and SUSAN SHIN, MD3 1
Department of Neurology, Warren Alpert Medical School of Brown University, Providence, Rhode island, USA Department of Radiology, Morristown Medical Center, Morristown, New Jersey, USA 3 Department of Neurology, Icahn School of Medicine at Mount Sinai, 1468 Madison Avenue, Annenberg Second Floor, Box 1052, New York, New York, 10029, USA 2
Accepted 11 November 2015 ABSTRACT: Introduction: Carpal tunnel syndrome (CTS) is a common clinical syndrome seen in the outpatient setting that is easily confirmed by electrodiagnostic testing. Methods: We describe the case of a patient who presented with the classic symptoms and neurological examination for CTS, but had a normal nerve conduction study and electromyogram. Results: Neuromuscular ultrasound of the median nerve on the symptomatic side revealed penetration of the nerve by a persistent median artery and vein in the mid-forearm, with a positive sonographic Tinel sign over this spot. This finding is an anatomical variation that has been described sparingly in the literature, mostly in cadavers. It has not been reported previously to be a mimic of CTS. Conclusions: This case demonstrates the diagnostic utility of neuromuscular ultrasound and the importance of considering an anatomical variation involving the median nerve in the differential diagnosis of CTS. Muscle Nerve 53:485–487, 2016
Carpal tunnel syndrome (CTS) is commonly encountered in the neurology clinic, and the diagnosis can be readily confirmed with nerve conduction study and electromyography. We describe the case of a patient who presented with classic history and neurological examination findings for CTS but had normal electrodiagnostic testing. Neuromuscular ultrasound done to search for a structural cause of the symptoms revealed an unusual anatomical variation proximal to the carpal tunnel, which resulted in a CTS mimic. CASE REPORT
A 47-year-old, right-handed man presented for evaluation of several years of left hand pain and paresthesias. Symptoms began as intermittent numbness and tingling in the left hand and progressed to become more constant and severe in the last year. The pain often woke him from
Additional Supporting Information may be found in the online version of this article. Abbreviations: AVM, arteriovenous malformation; CTS, carpal tunnel syndrome; CSA, cross-sectional area; PMA, persistent median artery; PMV, persistent median vein Key words: carpal tunnel syndrome; median nerve penetration; median neuropathy; neuromuscular ultrasound; persistent median artery Correspondence to: S. Shin; e-mail: [email protected] C 2015 Wiley Periodicals, Inc. V
Published online 13 November 2015 in Wiley Online Library (wileyonlinelibrary. com). DOI 10.1002/mus.24974
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sleep. Most of the paresthesias were localized to left digits 1–3. He did not have any neck pain, weakness, or any symptoms in the right hand. Neurological examination revealed normal strength and muscle bulk. Reflexes were 21 in all limbs. Sensation was diminished to pinprick in the left median nerve distribution, sparing the thenar eminence in the distribution of the palmar cutaneous branch of the median nerve. Otherwise, sensation was intact to all modalities in all extremities. Tinel and Phalen signs were not present at the wrist. Nerve conduction study showed no signs of a median neuropathy with normal left and right median nerve distal motor latencies and sensory nerve conduction studies (Table 1). Short segment incremental motor nerve conduction studies across the wrist were also normal. Electromyography of median-innervated muscles showed no abnormalities. Subsequently, diagnostic neuromuscular ultrasound of the left median nerve was performed in real time using a linear-array transducer (15L4; Terason, Burlington, Massachusetts). The median nerve cross-sectional area (CSA) was measured using a trace method done inside the hyperechoic epineurium. The left median nerve at the wrist had a normal, non-bifid appearance, with the exception of the presence of a persistent median artery and vein (Fig. 1A). The 2 vessels were distinguished by the compressibility of the vein and by the minimal compressibility and pulsatile, unidirectional flow of the artery. The CSA of the median nerve without the vascular structures at the wrist was measured to be 9 mm2. Ultrasound examination of the nerve approximately 6 cm proximal to the distal wrist crease revealed a focal region of enlargement of the nerve (CSA 16 mm2) (Fig. 1B); this was noted just distal to the site of penetration of the median nerve by the persistent median artery and vein. There was reunification of the separated nerve fibers immediately distal to the penetration site (Fig. 1; see also Video 1 in the Supplementary Material, available online). Pressure to this area from the ultrasound probe produced prominent paresthesias consistent with a sonographic Tinel MUSCLE & NERVE
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Table 1. Motor and sensory nerve conduction studies of the left median nerve.* Nerve and site
Distallatency (ms)
Amplitude (mV)
Conductionvelocity (m/s)
Left median motor NCS Wrist 3.5 7.8 Elbow 7.9 6.6 Left median sensory NCS Wrist 2.2 48 Left mixed palmar median and ulnar sensory NCS Palmar (median) 1.5 66 Palmar (ulnar) 1.6 29
— 55 60 59 55
NCS, nerve conduction study. *All values are within normal ranges.
sign. The contralateral median nerve was normal with a CSA of 9 mm2 at the wrist and mid-forearm. Subsequent MRI reported the presence of a persistent median artery, but it did not show the penetration of the nerve. The patient was started on gabapentin for neuropathic pain with nearcomplete resolution of his symptoms. Surgical exploration was not considered, as this finding is a normal anatomical variant, and the patient’s symptoms were well-controlled with gabapentin. DISCUSSION
This patient presented with symptoms and clinical examination that are classic for entrapment of the median nerve at the wrist. However nerve con-
duction study and electromyography failed to confirm this diagnosis. In addition, the prominent unilaterality of symptoms in his non-dominant hand is unusual for CTS. Further evaluation with neuromuscular ultrasound revealed the true pathology, consisting of penetration of the left median nerve by a persistent median artery and vein in the mid-forearm as the cause for the symptoms. The median artery provides blood supply to the hand in the developing fetus and typically regresses after the second month of gestation as the ulnar and radial arteries develop. The presence of a persistent median artery is not uncommon, with prevalence ranging from 4% to 16%.1 However, penetration of the median nerve by a persistent median artery is not widely reported. There have been several demonstrations of this anatomical variant in cadavers,1–3 and there have been 2 reports in living patients. In 1 case, the variant was discovered when the patient underwent ultrasound-guided median nerve block for median neuropathy,4 but the details of the clinical history and examination are not known. In the other case, the variant was discovered upon surgical exploration for suspected pronator teres syndrome.5 There has also been a report of an arteriovenous malformation (AVM) of a persistent median artery in a young boy with symptoms consistent with CTS in which the nerve bifurcated at the level of the AVM and did not
FIGURE 1. (A–F) Gray-scale ultrasound images of the left median nerve showing bisection by a persistent median artery (PMA) and vein (PMV). (A) Normal-appearing median nerve at the wrist along with a PMA and PMV. (B) Measurement approximately 6 cm proximal to the distal wrist crease shows the point of maximal enlargement of the nerve. Subsequent images are distal to proximal in sequence. For further detail, see Video 1 (see Supplementary Material, available online) which shows imaging of gray-scale ultrasound of the left median nerve bisected by the persistent median artery and vein. 486
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rejoin distally.6 There are other rare reports of structural compromise of the median nerve by other blood vessels, including the brachial artery,7 subscapular artery,8 and posterior circumflex humeral artery.8 All of these findings were seen in cadavers. Neuromuscular ultrasound has been proposed as a complement to electrodiagnostic studies for CTS and other peripheral neuropathies.9,10 By itself, there is strong evidence that neuromuscular ultrasound measurement of median nerve CSA at the wrist is an accurate test for the diagnosis of CTS.9 In addition, a recent study showed that, in about 50% of patients with a clinical diagnosis of CTS and normal nerve conduction studies, neuromuscular ultrasound was abnormal and confirmed the clinical diagnosis.11 When compared with conventional nerve conduction studies, neuromuscular ultrasound is superior for identification of anatomical variations that may be of particular importance to a surgeon, such as a bifid median nerve or persistent median artery, as well as pathological findings, such as cysts or neuromas.9 It is difficult to compare directly the sensitivity of neuromuscular ultrasound and electrodiagnostic studies for the diagnosis of CTS as most studies have used electrodiagnostic studies as the “gold standard.” Comparison of neuromuscular ultrasound with MRI for median neuropathy suggests that ultrasound has greater sensitivity and is more cost-efficient.12 This is consistent with the case described in this study, where the ultimate diagnosis was made by neuromuscular ultrasound and was not well visualized on MRI. In addition, in a recent study of ultrasound versus MRI for other focal peripheral neuropathies excluding CTS, ultrasound was also found to be more sensitive than MRI and with comparable specificity. Thus, ultrasound may be the preferred imaging modality for peripheral neuropathies.13
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The case described is an interesting example of the median nerve being penetrated by a persistent median artery and vein with rejoining of the nerve fibers into a single nerve immediately distal to the site of penetration. It demonstrates the importance of considering anatomical variations in the investigation of symptoms that are suggestive of the more common entity of CTS, but with inconsistent electrodiagnostic test results. These variants are especially important to consider in patients referred for surgery to avoid unnecessary intervention or inadvertent nerve injury. We have also highlighted the great diagnostic utility of neuromuscular ultrasound in the evaluation of these cases of structural anomalies, which may go unseen by conventional nerve conduction study, electromyography, or MRI. REFERENCES 1. Singla RK, Kaur N, Dhiraj GS. Prevalence of the persistent median artery. J Clin Diagn Res 2012;6:1454–1457. 2. Srivastava SK, Pande BS. Anomalous pattern of median artery in the forearm of Indians. Acta Anat (Basel) 1990;138:193–194. 3. Sanudo JR, Chikwe J, Evans SE. Anomalous median nerve associated with a persistent median artery. J Anat 1994;185:447–451. 4. Dolan J, Milligan P. Persistent median artery and veins in patients undergoing elective day case hand surgery. Reg Anesth Pain Med 2013;38:462–463. 5. Jones NF, Ming NL. Persistent median artery as a cause of pronator syndrome. J Hand Surg 1988;13:728–732. 6. Gutowski KA, Olivier WA, Mehrara BJ, Friedman DW. Arteriovenous malformation of a persistent median artery with a bifurcated median nerve. Plast Reconstr Surg 2000;106:1336–1339. 7. Roy TS. Median nerve penetration by a muscular branch of the brachial artery. Clin Anat 2003;16:335–339. 8. Miller RA. Observations upon the arrangement of the axillary artery and brachial plexus. Am J Anat 1939;64:143–163. 9. Cartwright MS, Hobson-Webb LD, Boon AJ, Alter KE, Hunt CH, Flores VH, et al. Evidence-based guideline: neuromuscular ultrasound for the diagnosis of carpal tunnel syndrome. Muscle Nerve 2012;46: 287–293. 10. Walker FO, Cartwright MS, Wiesler ER, Caress J. Ultrasound of nerve and muscle. Clin Neurophysiol 2004;115:495–507. 11. Al-Hashel JY, Rashad HM, Nouh MR, Amro HA, Khuraibet AJ, Shamov T, et al. Sonography in carpal tunnel syndrome with normal nerve conduction studies. Muscle Nerve 2015;51:592–597. 12. Deniz FE, Okusz E, Sarikaya B, Kurt S, Erkorkmaz U, Ulusoy H, et al. Comparison of the diagnostic utility of electromyography, ultrasonography, computed tomography, and magnetic resonance imaging in idiopathic carpal tunnel syndrome determined by clinical findings. Neurosurgery 2012;70:610–616. 13. Zaidman CM, Seelig MJ, Baker JC, Mackinnon SE, Pestronk A. Detection of peripheral nerve pathology. Neurology 2013;80:1634–1640.
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