1630 - Utility of Mid-Palmar Studies in Evaluating Proximal Median Mononeuropathy: A Case Report

A 73-year-old female presented with a 4–5 month history of right hand weakness and numbness involving the first three digits. Symptoms were most prominent at night, and she reported frequent dropping of objects. Physical exam was significant for a right ventral forearm mass and positive Tinel’s sign at the wrist. An electrodiagnostic evaluation was pursued, including EMG and NCS studies.

Findings demonstrated prolonged right median sensory latency and decreased amplitude across the wrist segment. However, mid-palmar studies did not show slowing across the wrist, indicating preserved distal conduction. Proximal right median nerve stimulation revealed reduced amplitude and conduction velocity across the forearm mass segment. EMG of the right APB muscle revealed decreased recruitment, consistent with axonal loss. No evidence of cervical radiculopathy, ulnar, radial, or brachial plexus involvement was identified.

Discussions:

This case underscores the diagnostic complexity of proximal median mononeuropathies. Traditional median NCS across the wrist segment may not adequately localize the lesion when pathology exists more proximally. Mid-palmar studies provide additional value by isolating distal conduction and determining the involvement of carpal tunnel entrapment. In this case, a latency difference of 0.7 ms across the wrist alongside abnormal proximal findings strongly supported a proximal lesion at the level of the forearm mass. The distinction was critical for management decisions since initial findings without a mid-palmar study could suggest a concomitant carpal tunnel syndrome.

Conclusions:

Mid-palmar nerve conduction studies can play a pivotal role in the electrodiagnostic evaluation of proximal median neuropathies. By confirming preserved distal conduction, these studies help localize pathology and prevent misdiagnosis, which is essential in guiding appropriate surgical and clinical intervention.