EDITORIAL
What role for ultrasound in diagnosing carpal tunnel syndrome? Jennifer M Dineen,1 Steven A Greenberg1,2 1
Department of Neurology, Brigham and Women’s Hospital and Harvard Medical School, Boston, Massachusetts, USA 2 Children’s Hospital Informatics Program, Harvard Medical School and Harvard-MIT Division of Health Sciences and Technology, Boston, Massachusetts, USA Correspondence to Dr Jennifer M Dineen, Department of Neurology, Brigham and Women’s Hospital, 75 Francis Street, Boston, MA 02115, USA; [email protected] Accepted 22 April 2014
To cite: Dineen JM, Greenberg SA. Pract Neurol Published Online First: [ please include Day Month Year] doi:10.1136/practneurol2014-000833
Carpal tunnel syndrome is the most common compressive neuropathy in the upper limb with a prevalence of 3–5% in the general population and a cost exceeding $500 million annually in the USA.1 2 It significantly impacts upon quality of life, and especially on a person’s ability to do manual labour or any task involving repetitive wrist movement. The diagnosis of carpal tunnel syndrome is currently clinical and through an electrodiagnostic evaluation that includes nerve conduction studies and needle electromyography.2 Nerve conduction measurements include peak latencies, conduction velocities and amplitudes of motor, sensory and mixed nerve responses, providing information as to the likely localisation and severity of a median neuropathy. In particular, comparing median with ulnar mixed nerve palmar responses is highly sensitive, as these fibres are affected early.3 The addition of needle electromyography helps to assess for cervical radiculopathy, proximal median neuropathy or polyneuropathy, as well as identifying axonal loss; it helps especially if the presenting symptoms are atypical. Identifying axonal loss influences clinical management as it suggests the need to bypass conservative therapy and proceed to surgical release. The disadvantages of electrodiagnostic studies are their cost, the inability to assess the surrounding anatomy and patient discomfort.2 While such studies are largely considered as the gold standard for diagnosing carpal tunnel syndrome, they can be normal in 16–34% of patients with clinically defined disease.1 Because there is not one test that accurately diagnoses carpal tunnel syndrome all of the time, we need to look for tests that can do this. Ultrasound scanning has, in recent years, been considered a valuable tool in diagnosing carpal tunnel syndrome. It has some advantages over electrodiagnostic studies, primarily that it is inexpensive and painless. The question remains
Dineen JM, et al. Pract Neurol 2014;0:1–2. doi:10.1136/practneurol-2014-000833
whether it is a good diagnostic tool on its own, useful as an initial screening test, or a complementary aid in diagnosing carpal tunnel syndrome? Of the many measurements assessed by neuromuscular ultrasound scanning, an increased cross-sectional area of the median nerve at the wrist (figure 1) is the most sensitive and specific finding in carpal tunnel syndrome.1 Thenar muscle and flexor retinaculum thickness reflect the increased median nerve latency on nerve conduction studies and perhaps indicate worsening of carpal tunnel syndrome.4 It is worth noting that ultrasound of the carpal tunnel can alter treatment by identifying anatomical factors that contribute to nerve entrapment but which electrodiagnostic studies will overlook—showing changes consistent with carpal tunnel syndrome— such as a neuroma or schwannoma.2 Ultrasound scanning can also help when the carpal tunnel syndrome is so severe that all median nerve electrodiagnostic responses are absent, preventing definitive localisation of the median neuropathy to the wrist. Neuromuscular ultrasound may also help in the patient whose symptoms persist following carpal tunnel decompression; ultrasound may show that the flexor retinaculum has not been adequately divided. While neuromuscular ultrasound can provide useful information, a disadvantage is that it cannot establish the extent of axonal loss and thus cannot address prognosis. It also cannot exclude coexisting neuromuscular conditions or fully investigate alternative causes of a patient’s hand numbness.2 A particular limitation of ultrasound scanning is that the published medical literature shows a variable performance in diagnosing carpal tunnel syndrome. Sensitivities range from 57% to 99% and specificities from 22% to 100%.1 A low sensitivity means patients with carpal tunnel syndrome may test negatively by ultrasound, while a low specificity means patients with other conditions get 1
EDITORIAL
Figure 1 Ultrasound scan of the median nerve at the wrist. (A) Normal median nerve with cross-sectional area of 8 mm2. (B) Abnormal median nerve in carpal tunnel syndrome with cross-sectional area of 15 mm2. Focal nerve enlargement at or near the carpal tunnel is typical of carpal tunnel syndrome, possibly relating to subperineurial oedema. Image courtesy of Amanda C Guidon, MD Department of Neurology, Massachusetts General Hospital, Boston, Massachusetts, USA.
misdiagnosed by ultrasound as having carpal tunnel syndrome. This high degree of variability is partly due to differing methods pertaining to choices of gold standards (clinical diagnosis or combined clinical and neurophysiological diagnosis), diagnostic criteria (crosssectional area cut-off values ranging from 6.5 mm2 to 15.0 mm2) and control populations (healthy volunteers or non-carpal tunnel syndrome disease controls). However, ultrasound diagnostic performance differs markedly even between studies with identical standards and cut-offs (eg, specificity of 22% in one study, 70% in another). The very low specificity of a 9 mm2 crosssectional area cut-off (22%) of one study5 suggests that ultrasound may be very limited as a stand-alone highly sensitive diagnostic test. Ultrasound might instead be useful as a screening test performed first to avoid later performing portions of electrodiagnosis; for example, patients falling below a 99% sensitivity cut-off (such as 9 mm2) are so unlikely to have carpal tunnel syndrome that nerve conduction studies of the median nerve might be avoided.5 However, patients might still need other portions of electrodiagnosis to address the cause of their symptoms. Because so few patients might have cross-sectional areas below a highly sensitive cut-off, such an approach could require performing many times more ultrasounds than the number of median nerve studies avoided, an approach with an unfavourable cost/ benefit trade-off. Ultimately, we need to decide how these tests can help to choose a suitable management for the patient’s problem. For those with a clinical diagnosis of carpal tunnel syndrome for whom further diagnostic testing is indicated, electrodiagnostic studies should be done initially as they give a diagnosis and prognosis by categorising the syndrome as mild, moderate or severe, based on the presence of axonal loss. This is where ultrasound is limited as it cannot assess for axonal loss and crosssectional area does not correlate with electrodiagnosisdefined severity.5 Ultrasound for carpal tunnel syndrome is not a good diagnostic tool on its own because
2
its specificity is not high enough at thresholds that give reasonable sensitivities. Ultrasound is not a good initial screening test as one might have to screen many times more patients by ultrasound than the number of electrodiagnosis studies subsequently avoided.4 On the other hand, ultrasound can identify structural or anatomical abnormalities that electrodiagnosis studies cannot detect. In this regard, ultrasound complements the information obtained through electrodiagnostic studies. With more widespread use, the role of ultrasound in the diagnosis of carpal tunnel syndrome and its positive impact on patient care will be increasingly defined. Contributors JMD wrote the manuscript and revised it; SAG wrote and reviewed the manuscript and reviewed the revision. Competing interests None. Provenance and peer review Commissioned; externally peer reviewed. This paper was reviewed by Roger Whittaker, Newcastle upon Tyne, UK, and Jeremy Bland, Kent, UK.
REFERENCES 1 Fowler JR, Gaughan JP, Ilyas AM. The sensitivity and specificity of ultrasound for the diagnosis of carpal tunnel syndrome: a meta-analysis. Clin Orthop Relat Res 2011;469:1089–94. 2 Cartwright MS, Hobson-Webb LD, Boon AJ, et al. Evidence-based guideline: neuromuscular ultrasound for the diagnosis of carpal tunnel syndrome. Muscle Nerve 2012;46:287–93. 3 American Association of Electrodiagnostic Medicine CTS Task Force. Practice parameter for electrodiagnostic studies in carpal tunnel syndrome: summary statement. Muscle Nerve 2002;25:918–22. 4 Kim JM, Kim MW, Ko YJ. Correlating ultrasound findings of carpal tunnel syndrome with nerve conduction studies. Muscle Nerve 2013;48:905–10. 5 Mhoon JT, Juel VC, Hobson-Webb LD. Median nerve ultrasound as a screening tool in carpal tunnel syndrome: correlation of cross sectional area measures with electrodiagnostic abnormality. Muscle Nerve 2012; 46:871–8.
Dineen JM, et al. Pract Neurol 2014;0:1–2. doi:10.1136/practneurol-2014-000833
What role for ultrasound in diagnosing carpal tunnel syndrome? Jennifer M Dineen,1 Steven A Greenberg1,2 1
Department of Neurology, Brigham and Women’s Hospital and Harvard Medical School, Boston, Massachusetts, USA 2 Children’s Hospital Informatics Program, Harvard Medical School and Harvard-MIT Division of Health Sciences and Technology, Boston, Massachusetts, USA Correspondence to Dr Jennifer M Dineen, Department of Neurology, Brigham and Women’s Hospital, 75 Francis Street, Boston, MA 02115, USA; [email protected] Accepted 22 April 2014
To cite: Dineen JM, Greenberg SA. Pract Neurol Published Online First: [ please include Day Month Year] doi:10.1136/practneurol2014-000833
Carpal tunnel syndrome is the most common compressive neuropathy in the upper limb with a prevalence of 3–5% in the general population and a cost exceeding $500 million annually in the USA.1 2 It significantly impacts upon quality of life, and especially on a person’s ability to do manual labour or any task involving repetitive wrist movement. The diagnosis of carpal tunnel syndrome is currently clinical and through an electrodiagnostic evaluation that includes nerve conduction studies and needle electromyography.2 Nerve conduction measurements include peak latencies, conduction velocities and amplitudes of motor, sensory and mixed nerve responses, providing information as to the likely localisation and severity of a median neuropathy. In particular, comparing median with ulnar mixed nerve palmar responses is highly sensitive, as these fibres are affected early.3 The addition of needle electromyography helps to assess for cervical radiculopathy, proximal median neuropathy or polyneuropathy, as well as identifying axonal loss; it helps especially if the presenting symptoms are atypical. Identifying axonal loss influences clinical management as it suggests the need to bypass conservative therapy and proceed to surgical release. The disadvantages of electrodiagnostic studies are their cost, the inability to assess the surrounding anatomy and patient discomfort.2 While such studies are largely considered as the gold standard for diagnosing carpal tunnel syndrome, they can be normal in 16–34% of patients with clinically defined disease.1 Because there is not one test that accurately diagnoses carpal tunnel syndrome all of the time, we need to look for tests that can do this. Ultrasound scanning has, in recent years, been considered a valuable tool in diagnosing carpal tunnel syndrome. It has some advantages over electrodiagnostic studies, primarily that it is inexpensive and painless. The question remains
Dineen JM, et al. Pract Neurol 2014;0:1–2. doi:10.1136/practneurol-2014-000833
whether it is a good diagnostic tool on its own, useful as an initial screening test, or a complementary aid in diagnosing carpal tunnel syndrome? Of the many measurements assessed by neuromuscular ultrasound scanning, an increased cross-sectional area of the median nerve at the wrist (figure 1) is the most sensitive and specific finding in carpal tunnel syndrome.1 Thenar muscle and flexor retinaculum thickness reflect the increased median nerve latency on nerve conduction studies and perhaps indicate worsening of carpal tunnel syndrome.4 It is worth noting that ultrasound of the carpal tunnel can alter treatment by identifying anatomical factors that contribute to nerve entrapment but which electrodiagnostic studies will overlook—showing changes consistent with carpal tunnel syndrome— such as a neuroma or schwannoma.2 Ultrasound scanning can also help when the carpal tunnel syndrome is so severe that all median nerve electrodiagnostic responses are absent, preventing definitive localisation of the median neuropathy to the wrist. Neuromuscular ultrasound may also help in the patient whose symptoms persist following carpal tunnel decompression; ultrasound may show that the flexor retinaculum has not been adequately divided. While neuromuscular ultrasound can provide useful information, a disadvantage is that it cannot establish the extent of axonal loss and thus cannot address prognosis. It also cannot exclude coexisting neuromuscular conditions or fully investigate alternative causes of a patient’s hand numbness.2 A particular limitation of ultrasound scanning is that the published medical literature shows a variable performance in diagnosing carpal tunnel syndrome. Sensitivities range from 57% to 99% and specificities from 22% to 100%.1 A low sensitivity means patients with carpal tunnel syndrome may test negatively by ultrasound, while a low specificity means patients with other conditions get 1
EDITORIAL
Figure 1 Ultrasound scan of the median nerve at the wrist. (A) Normal median nerve with cross-sectional area of 8 mm2. (B) Abnormal median nerve in carpal tunnel syndrome with cross-sectional area of 15 mm2. Focal nerve enlargement at or near the carpal tunnel is typical of carpal tunnel syndrome, possibly relating to subperineurial oedema. Image courtesy of Amanda C Guidon, MD Department of Neurology, Massachusetts General Hospital, Boston, Massachusetts, USA.
misdiagnosed by ultrasound as having carpal tunnel syndrome. This high degree of variability is partly due to differing methods pertaining to choices of gold standards (clinical diagnosis or combined clinical and neurophysiological diagnosis), diagnostic criteria (crosssectional area cut-off values ranging from 6.5 mm2 to 15.0 mm2) and control populations (healthy volunteers or non-carpal tunnel syndrome disease controls). However, ultrasound diagnostic performance differs markedly even between studies with identical standards and cut-offs (eg, specificity of 22% in one study, 70% in another). The very low specificity of a 9 mm2 crosssectional area cut-off (22%) of one study5 suggests that ultrasound may be very limited as a stand-alone highly sensitive diagnostic test. Ultrasound might instead be useful as a screening test performed first to avoid later performing portions of electrodiagnosis; for example, patients falling below a 99% sensitivity cut-off (such as 9 mm2) are so unlikely to have carpal tunnel syndrome that nerve conduction studies of the median nerve might be avoided.5 However, patients might still need other portions of electrodiagnosis to address the cause of their symptoms. Because so few patients might have cross-sectional areas below a highly sensitive cut-off, such an approach could require performing many times more ultrasounds than the number of median nerve studies avoided, an approach with an unfavourable cost/ benefit trade-off. Ultimately, we need to decide how these tests can help to choose a suitable management for the patient’s problem. For those with a clinical diagnosis of carpal tunnel syndrome for whom further diagnostic testing is indicated, electrodiagnostic studies should be done initially as they give a diagnosis and prognosis by categorising the syndrome as mild, moderate or severe, based on the presence of axonal loss. This is where ultrasound is limited as it cannot assess for axonal loss and crosssectional area does not correlate with electrodiagnosisdefined severity.5 Ultrasound for carpal tunnel syndrome is not a good diagnostic tool on its own because
2
its specificity is not high enough at thresholds that give reasonable sensitivities. Ultrasound is not a good initial screening test as one might have to screen many times more patients by ultrasound than the number of electrodiagnosis studies subsequently avoided.4 On the other hand, ultrasound can identify structural or anatomical abnormalities that electrodiagnosis studies cannot detect. In this regard, ultrasound complements the information obtained through electrodiagnostic studies. With more widespread use, the role of ultrasound in the diagnosis of carpal tunnel syndrome and its positive impact on patient care will be increasingly defined. Contributors JMD wrote the manuscript and revised it; SAG wrote and reviewed the manuscript and reviewed the revision. Competing interests None. Provenance and peer review Commissioned; externally peer reviewed. This paper was reviewed by Roger Whittaker, Newcastle upon Tyne, UK, and Jeremy Bland, Kent, UK.
REFERENCES 1 Fowler JR, Gaughan JP, Ilyas AM. The sensitivity and specificity of ultrasound for the diagnosis of carpal tunnel syndrome: a meta-analysis. Clin Orthop Relat Res 2011;469:1089–94. 2 Cartwright MS, Hobson-Webb LD, Boon AJ, et al. Evidence-based guideline: neuromuscular ultrasound for the diagnosis of carpal tunnel syndrome. Muscle Nerve 2012;46:287–93. 3 American Association of Electrodiagnostic Medicine CTS Task Force. Practice parameter for electrodiagnostic studies in carpal tunnel syndrome: summary statement. Muscle Nerve 2002;25:918–22. 4 Kim JM, Kim MW, Ko YJ. Correlating ultrasound findings of carpal tunnel syndrome with nerve conduction studies. Muscle Nerve 2013;48:905–10. 5 Mhoon JT, Juel VC, Hobson-Webb LD. Median nerve ultrasound as a screening tool in carpal tunnel syndrome: correlation of cross sectional area measures with electrodiagnostic abnormality. Muscle Nerve 2012; 46:871–8.
Dineen JM, et al. Pract Neurol 2014;0:1–2. doi:10.1136/practneurol-2014-000833
