Idiopathic carpal tunnel syndrome. Clinical, electrodiagnostic, and magnetic resonance imaging correlations.

BACKGROUND: Although carpal tunnel syndrome is diagnosed primarily on clinical grounds, a number of investigations can be helpful in confirming the diagnosis and providing therapeutic orientation. Electrodiagnostic testing is the most widely used method in everyday practice but can be inconclusive or inconsistent with the clinical findings. Magnetic resonance imaging is useful in such cases.

OBJECTIVES: To compare the diagnostic usefulness of electrodiagnostic testing and magnetic resonance imaging in patients with carpal tunnel syndrome.

PATIENTS AND METHODS: Thirty-three cases of clinically-defined carpal tunnel syndrome in 20 patients were investigated by electrodiagnostic testing and magnetic resonance imaging. The nerve entrapment was categorized as mild, moderate, or severe based on clinical and electrodiagnostic findings. Structures evaluated on magnetic resonance imaging scans were the median nerve, the flexor retinaculum, the flexor tendons, the fat lying deep to the tendons, the thenar compartment, and the carpal bones.

RESULTS: Bowing of the transverse carpal ligament, high signal from the median nerve on T2 images, and median nerve enlargement were found in 70%, 57%, and 55% of cases, respectively. Bowing of the transverse carpal ligament is a cause of mechanical compression, whereas the other two signs reflect injury to the median nerve. High signal from the median nerve was associated with more severe clinical and/or electrodiagnostic abnormalities.

CONCLUSION: When electrodiagnostic abnormalities suggest more severe disease than expected or are otherwise discordant with clinical findings, demonstration by magnetic resonance imaging of high median nerve signal and/or median nerve enlargement may help to select those patients most likely to benefit from surgical treatment.