Diagnostic Neuromuscular Ultrasound to Confirm Clinical Significance of a Genetic Variant for Charcot-Marie-Tooth Type 4C: A Case Report.

Abstract: Neuromuscular ultrasound has emerged as a beneficial, complementary tool to electromyography (EMG) in the diagnosis of neuromuscular diseases as it provides high-resolution anatomic imaging of peripheral nerves and muscles. It has been used previously as an adjunct to EMG to diagnose Charcot-Marie-Tooth disease. Here, we present a case of a 64-yr-old man with bilateral sensorineural hearing loss of 14 yrs who presented to an outpatient neuromuscular clinic at a tertiary medical center with very slow progressive paresthesias. This case highlights the application of neuromuscular ultrasound to help confirm the presence of a likely Charcot-Marie-Tooth disease type 4C despite indeterminate genetic testing results and challenging EMG results. He had genetic testing which revealed a normal PMP22 gene; however, he had a variant of uncertain significance in the SH3TC2 gene which has shown associations with autosomal recessive CMT4C. Neuromuscular ultrasound revealed mild median and significant tibial nerve uniform enlargement throughout their course. There may also be utility in performing neuromuscular ultrasound on similarly affected family members if the same variant of uncertain significance returns for SH3TC2 , with consideration of both peripheral nerve and nerve root assessment.