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Acute Posterior Tarsal Tunnel Syndrome Caused by Gouty Tophus Tun Hing Lui Foot Ankle Spec published online 8 September 2014 DOI: 10.1177/1938640014548318 The online version of this article can be found at: http://fas.sagepub.com/content/early/2014/08/24/1938640014548318

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〈 Case Report 〉 Acute Posterior Tarsal Tunnel Syndrome Caused by Gouty Tophus Abstract: Gouty tophus of the tarsal tunnel is a rare cause of posterior tarsal tunnel syndrome. We present a case of acute posterior tarsal tunnel syndrome due to gouty tophus that required early tarsal tunnel release in order to avoid irreversible nerve damage. The presence of background neuropathy resulted in a less favorable result than expected. Levels of Evidence: Therapeutic, Level V: Case Report Keywords: tarsal tunnel syndrome; gout; tophus; neuropathy

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osterior tarsal tunnel syndrome (PTTS) involves damage to the tibial nerve when it lies under the flexor retinaculum on the medial side of the ankle.1 It is considered to be an entrapment neuropathy. Etiologic categories for PTTS include (a) trauma; (b) space-occupying lesions; (c) intrinsic pathological processes, such as synovitis; and (d) processes that produce tension on the nerve, such as varus or valgus deformities.2 Trauma causing PTTS includes displaced fracture, traumatic flexor tenosynovitis, and posttraumatic

Tun Hing Lui, MBBS (HK), FRCS (Edin), FHKAM, FHKCOS

epineural scarring.3 Space-occupying plantar foot numbness since October 2009. He did not seek medical lesions can compress the tibial nerve consultation for this problem. He was either from inside or outside the tarsal admitted to our department in November tunnel.3 Varicosities are the most 2010 for sudden onset of severe left common type of space-occupying lesion. plantar foot paraesthesia. Clinical Other includes ganglia, lipoma, examination showed multiple tophi over neurilemmoma,4 bony exostosis, medial his left foot and ankle level with swelling talocalcaneal bar, flexor digitorum accessorial longus muscle,5 and hypertrophic accessory Posterior tarsal tunnel syndrome abductor hallucis muscle.3 We present a (PTTS) involves damage to the tibial nerve case of acute tarsal when it lies under the flexor retinaculum tunnel syndrome due to compression of the on the medial side of the ankle.” tibial nerve and its branches by a gouty tophus. at the tarsal tunnel (Figure 1) region. Light touch sensation was impaired over Case Report the territories of the left medial and A 53-year-old gentleman suffered from lateral plantar nerves. Tinel’s sign was tophaceous gout. He had history of left positive over the left tarsal tunnel. carpal tunnel syndrome on November Radiographs showed multiple old 2009 with open carpal tunnel release metatarsal fractures of both feet with done. Intraoperative findings showed callus formation (Figure 2). There was no tophaceous deposit embedded in history of trauma to the feet or diabetes between flexor tendons with attenuated mellitus. Blood glucose and HbA1c levels flexor digitorum profundus tendons. were normal. Magnetic resonance image Postoperatively, the hand symptoms of his left foot and ankle showed spacemostly subsided. He complained of left occupying lesion at the tarsal tunnel

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DOI: 10.1177/1938640014548318. From the Department of Orthopaedics and Traumatology, North District Hospital, Hong Kong SAR, China. Address correspondence to Tun Hing Lui, MBBS (HK), FRCS (Edin), FHKAM, FHKCOS, Department of Orthopaedics and Traumatology, North District Hospital, 9 Po Kin Road, Sheung Shui, NT, Hong Kong SAR, China; e-mail: [email protected]. For reprints and permissions queries, please visit SAGE’s Web site at http://www.sagepub.com/journalsPermissions.nav. Copyright © 2014 The Author(s)

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Figure 1. Clinical photos showed multiple tophi over his left foot and ankle level with swelling at the tarsal tunnel.

compression of the neurovascular bundle. The flexor hallucis longus tendon was not involved (Figure 4). The left plantar foot paraesthesia subsided immediately after the operation. However, the background plantar foot numbness persisted with decrease in light touch sensation. Electromyography (EMG) was performed and showed evidence of polyneuropathy and left S1 radiculopathy. Magnetic resonance image of his lumbosacral spine showed dessicated L3/4 and L4/5 discs with mild posterior bulging of the L4/5 disc. The neural foramina were patent. There was no evidence of central spinal stenosis or gouty facet arthritis. On 22 months of follow-up, his left foot neurological condition was static with persistent plantar sole numbness without any paraesthesia. He managed to resume duty as a security guard.

Discussion Figure 2. (A) Radiographs showed multiple old metatarsal fractures of both feet with callus formation. (B) X-rays of the ankles show no significant articular or periarticular bone erosions.

(Figure 3). Open tarsal tunnel release and debridement of the tophaceous deposit was performed. Intraoperative

findings showed tophaceous deposit extended from the retrocalcaneal space down to abductor hallucis causing

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Posterior tarsal tunnel syndrome results from compressive entrapment of the posterior tibial nerve. Many reports compared it to carpal tunnel syndrome. However, it is not the tarsal tunnel, but the medial plantar tunnel, that is analogous to the carpal tunnel; the flexor retinaculum is analogous to the forearm fascia.6 Studies have shown that it is a different clinical entity with respect to anatomy, cause, pathophysiology, clinical presentation, and response to nonsurgical and surgical treatment.3 Causes of PTTS are 50% idiopathic and 50% mechanical owing to a space-occupying lesion.5 Acute tarsal tunnel syndrome is often encountered after marathon races as an acute effect of unusual mechanical stress.1 Gouty tophus is a rare cause of PTTS, and there have been only sporadic case reports in the English literature.2,7 In contrast to the previous reports, our patient had different clinical presentation and response to surgical decompression. The previous reported cases are cases of chronic PTTS due to gouty tophus with complete relief of symptoms after the excision of the tophus together with tarsal tunnel

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Figure 3. MRI showed space occupying lesion at the tarsal tunnel: (A, B) sagittal view; (C) transverse view; (D) coronal view.

Figure 4. (A) Open exploration of the tarsal tunnel showed the presence of gouty tophus (arrow). The flexor hallucis longus tendon (pointed by the forceps tip) was not involved. (B After debridement of the tophus.

release.2,7 Our patient had a background history of plantar foot numbness for 1 year and superimposed with a 1-week history of plantar foot paraesthesia. The

acute-onset symptom was the most disturbing one and affected walking. This was the main reason for the patient to seek medical help.

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Magnetic resonance imaging (MRI) was performed to detect any space-occupying lesion within the tarsal tunnel. However, gouty tophus in MRI could be confused with different disorders, including neoplasms, pigmented villonodular synovitis, and synovial osteochondromatosis. Moreover, nonoperative treatment is contraindicated in acute cases of PTTS with a spaceoccupying lesion.3 Therefore, open exploration and release of the tarsal tunnel has been performed in this patient for both diagnostic and therapeutic purposes. Although there was report suggesting surgical treatment to prevent irreversible damage to the median and ulnar nerves in case of entrapment neuropathy caused by tophaceous gout,8 we are not sure whether irreversible nerve damage would occur in this case if nonoperative treatment was used. Electrodiagnostic studies were not performed before the operation for 2 reasons: (a) in the presence of pain and paraesthesia in the foot and a positive Tinel’s sign at the tarsal tunnel, normal electrodiagnostic studies do not exclude the diagnosis of PTTS3 and (b) it would delay surgery in this acute stage of the disease.9 Preoperative MRI usually cannot determine the precise location of entrapment or signal intensity abnormalities or morphologic changes of peripheral nerves.5 Therefore, complete release of the tarsal tunnel together with the fibrous tunnels of the branches of the tibial nerve6 and excision of the gouty tophus were performed. Surgical decompression relieved the acute-onset symptoms but not the background sole numbness of this patient. The 2 main possibilities under consideration are the following: (a) other pathologies of the tibial nerve besides compressive entrapment and (b) double crush syndrome. Clinically, there was no hindfoot valgus deformity producing tension on the posterior tibial nerve. Epineural scarring and incomplete release are well-known causes of failure of tarsal tunnel release.3 The flexor retinaculum of the tarsal tunnel and the fibro-osseous tunnels of

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the medial and lateral plantar nerves were completely released. Moreover, no evidence of epineural scarring was noted intraoperatively. In the presence of a space-occupying lesion, it is important to rule out sites of nerve entrapment more proximally. This is referred to as a “double crush” syndrome. The additional nerve lesion can be any neuronal insult resulting from mechanical compression, mechanical tension, and/or diffuse axonal abnormality like diabetes mellitus.3 Although EMG suggested the presence of left S1 radiculopathy, the patient did not have any back pain or clinical sign suggestive of S1 radiculopathy. Moreover, MRI of the lumbosacral spine excluded the presence of gouty facet arthritis10 or S1 nerve root compression although possibility of prior disc bulge that has receded cannot be precluded. The presence of multiple old metatarsal fractures of both feet without history of trauma suggested a more generalized problem of the nervous system. EMG suggested the presence of polyneuropathy. Although diabetes mellitus is the most common cause of neuropathy, there was no evidence of

diabetes in this patient. The hyperuricemia of gout may produce a treatable form of peripheral neuropathy,11 and the presence of neuropathy predisposes the peripheral nerve to chronic compression.6 In summary, this was a case of acute PTTS due to tophaceous deposit at the tarsal tunnel. Early operation was performed to prevent irreversible nerve damage.12 However, subjective satisfaction was less favorable than expected.13 This was due to the background neuropathy.

References 1. Antoniadis G, Scheglmann K. Posterior tarsal tunnel syndrome: diagnosis and treatment. Dtsch Arztebl Int. 2008;105: 776-781. 2. Estrada A, Hall R, Martinez S, Allen NB. Gouty tophus causing tarsal tunnel syndrome. J Clin Rheumatol. 1996;2: 293-297.

5. Duran-Stanton AM, Bui-Mansfield LT. Magnetic resonance diagnosis of tarsal tunnel syndrome due to flexor digitorum accessorius longus and peroneocalcaneus internus muscles. J Comput Assist Tomogr. 2010;34:270-272. 6. Rosson GD, Larson AR, Williams EH, Dellon AL. Tibial nerve decompression in patients with tarsal tunnel syndrome: pressures in the tarsal, medial plantar, and lateral plantar tunnels. Plast Reconstr Surg. 2009;124:1202-1210. 7. Wakabayashi T, Irie K, Yamanaka H, Iwatani M, Inoue K. Tarsal tunnel syndrome caused by tophaceous gout. A case report. J Clin Rheumatol. 1998;4:151-155. 8. Akizuki S, Matsui T. Entrapment neuropathy caused by tophaceous gout. J Hand Surg Br. 1984;9:331-332. 9. Pai CH, Tseng CH. Acute carpal tunnel syndrome caused by tophaceous gout. J Hand Surg Am. 1993;18:667-669. 10. Chang IC. Surgical versus pharmacologic treatment of intraspinal gout. Clin Orthop Relat Res. 2005;(433):106-110. 11. Delaney P. Gouty neuropathy. Arch Neurol. 1983;40:823-824.

3. Lau JTC, Daniels TR. Tarsal tunnel syndrome: a review of the literature. Foot Ankle Int. 1999;20:201-209.

12. Sammarco GJ, Chang LJ. Outcome of surgical treatment of tarsal tunnel syndrome. Foot Ankle Int. 2003;24:125-131.

4. Kwok KB, Lui TH, Lo WN. Neurilemmoma of the first branch of the lateral plantar nerve causing tarsal tunnel syndrome. Foot Ankle Spec. 2009;2:287-290.

13. Sung KS, Park SJ. Short-term operative outcome of tarsal tunnel syndrome due to benign space-occupying lesions. Foot Ankle Int. 2009;30:741-745.

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