A Rare Case of Median Mononeuropathy

Case Diagnosis: Proximal right-sided median mononeuropathy at the distal humerus with acute denervation-related intramuscular edema of the pronator teres, flexor carpi radialis, and pronator quadratus.

Case Description: A 40-year-old female presented with right hand weakness when flexing her thumb at the interphalangeal joint and forearm pain 4 months in duration. She denied trauma but acknowledged the pain began following a ski trip, with paresthesia occurring intermittently in the right first and second digits. X-rays of her right wrist were negative; cervical MRI revealed disc bulges at C5-6 and C6-7. ⅖ strength was noted in right forearm pronation and trace strength was noted in the right flexor pollicis longus; exam was otherwise unremarkable.

Discussion: Results suggest a possible point of median nerve compression at the ligament of Struthers. Compression of the median nerve at the carpal tunnel is common, but other locations are not. Prevalence of the ligament of Struthers is rare, occurring in 0.7-2.5% of the population, with symptoms of median nerve impingement there even rarer. Confirmation and treatment include surgical release of the ligament for nerve decompression.

Setting: Outpatient Physiatry Clinic

Assessment/Results: Right upper extremity NCS was normal. EMG needle findings demonstrated positive sharp waves and decreased recruitment in the right PT, FPL, and PQ muscles. All other muscles tested were normal. Electrodiagnostic evidence was consistent with a proximal right-sided median neuropathy, with findings suggestive of pathology proximal to the takeoff of the innervation to the PT. MRI of the right upper extremity indicated increased signal within the median nerve at the distal humerus, suspicious for median nerve compression at the ligament of Struthers. MRI also indicated an intramuscular edema-like signal predominantly at the PT, FCR, and PQ.

Conclusion: Mononeuropathy due to impingement at the ligament of Struthers is rare. Utilization of MRI and NCS/EMG can be adjuvants in directing appropriate diagnosis and treatment.