Clinical and Electrodiagnostic Correlations of Ultrasound-Detected Markedly Enlarged Median Nerve at the Wrist.

Background/objectives: This is a retrospective review of 36 patients with electrodiagnostic (EDX) confirmation of carpal tunnel syndrome (CTS) and ultrasound (US) detection of marked median nerve enlargement (defined as a cross-sectional area [CSA] of 40 mm² or greater) at the wrist.

Methods: We describe the clinical, electrodiagnostic (EDX), and US findings in these patients and discuss the pathophysiologic basis of a markedly enlarged median nerve.

Results: The markedly enlarged median nerve was detected by US in a total of 39 hands (36 patients, with 3 bilateral). Of the 39 hands, thenar atrophy was observed in 15 (38.5%) hands, and pinprick loss in the median nerve distribution was noted in all hands. Moderately severe or severe median nerve entrapment at the carpal tunnel (CT) was confirmed by EDX studies in 21 (53.8%) and 16 (41.0%) hands, respectively. A total of 12 (30.8%) hands had no compound muscle action potentials (CMAPs) over the abductor pollicis brevis muscle, and sensory nerve action potentials (SNAPs) were not detected in 31 (79.5%) hands. The wrist CSA was between 40 and 44 mm² in 20 (51.3%) hands, between 45 and 49 mm² in 13 (33.3%) hands, and 50 mm² or greater in 6 (15.4%) hands.

Conclusions: The implications of the markedly enlarged median nerve for surgical management of CTS are unknown, and future prospective studies are needed.