Superimposed Carpal Tunnel Syndrome in a Patient with Charcot-Marie-Tooth Disease Type 1A: Case Report and Diagnostic Considerations.

INTRODUCTION: We present a case of Charcot-Marie-Tooth disease type 1A (CMT1A) complicated by symptoms concerning for superimposed carpal tunnel syndrome (CTS). Diagnostic interpretation was challenging due to overlapping electrodiagnostic and ultrasound findings typical of CMT1A. CASE PRESENTATION: A 54-year-old woman with genetically confirmed CMT1A reported bilateral intermittent burning, numbness, and tingling in digits 1-3, worse at night and with hand use. Physical exam revealed positive Tinel's and Phalen's signs bilaterally with preserved motor strength and no thenar atrophy. Electrodiagnostic studies showed diffuse demyelinating polyneuropathy, consistent with CMT1A, with slowed conduction velocities in all nerves tested and prolonged sensory peak latencies in both median and ulnar nerves. Neuromuscular ultrasound revealed diffuse nerve enlargement consistent with hereditary neuropathy. However, focal enlargement of the median nerves at the carpal tunnel - 13 mm2 on the right and 12 mm2 on the left - yielded elevated wrist-to-forearm ratios of 1.44 and 1.75, respectively, suggestive of superimposed CTS. Ultrasound-guided corticosteroid injection served both diagnostic and therapeutic purposes, bridging the patient to appropriate definitive management with carpal tunnel release and ultimately an excellent clinical outcome. CONCLUSION: CTS and CMT1A share overlapping clinical and diagnostic features which complicates the recognition of a superimposed entrapment neuropathy. In patients with hereditary neuropathies, new focal symptoms should prompt consideration of superimposed compressive or entrapment neuropathies. In this case, the multimodal approach which entailed electrodiagnostics, ultrasound, and a therapeutic response to corticosteroid injection enabled accurate identification and effective treatment.