463 - Sequence My Genome – More Than Just a Numb Thumb

Case Diagnosis: Distal Hereditary Motor Neuropathy

Case Description: A 34-year-old right-handed male with no past medical history presented for EMG/NCS due to bilateral hand weakness and painful paresthesia’s specifically in the first 3 digits for two years. He also reported gait instability due to high arches, which his father had experienced as well. The patient’s physical examination was significant for intrinsic muscle atrophy of bilateral hands with diminished grip strength, bilateral calf and foot intrinsic muscle atrophy, as well as diffusely absent deep tendon reflexes. Electrodiagnostic testing revealed severe bilateral median nerve entrapment neuropathy at the wrists, mild left ulnar nerve entrapment at the elbow, and underlying axonal peripheral motor neuropathy consistent with an inherited peripheral motor neuropathy. Given his clinical picture and EDX findings he was referred to neurology for genetic testing which confirmed the diagnosis of Distal Hereditary Motor Neuropathy (dHMN).

Discussions: While clinical symptoms may be helpful, various inherited disorders exist under a constellation of subtypes. Patients with inherited mono and polyneuropathies often require further testing for proper diagnosis including copper, B12/folate levels, immunofixation, and chromosome analysis. In our patient, Charcot-Marie-Tooth (CMT) was initially suspected given his clinical symptoms but genetic testing for CMT was negative. Comprehensive genetic sequencing was significant for loss-of-function mutations in SIGMAR1 gene which is associated with Autosomal Recessive Distal Spinal Muscular Atrophy, also known as Distal Hereditary Motor Neuropathy.

Conclusions: This is a rare case of a patient who was initially referred for an EMG/NCS due to suspicions of carpal tunnel syndrome. However, upon closer examination and questioning it was evident a more profound pathology ongoing. This case highlights the importance of obtaining a thorough history and neurological examination to obtain proper diagnosis and treatment planning, as well as the value of appropriate laboratory testing.