Attending Physician Carl T. Hayden Veterans' Administration Medical Center Phoenix, Arizona, United States
Case Diagnosis: Large plexiform nerve sheath tumor from elbow to wrist presenting as carpal tunnel syndrome
Case Description: A 62 year old right hand dominant male was referred for electrodiagnostic studies to evaluate left hand paresthesia. He endorsed three years of intermittent paresthesia and itchiness in his left second and third digits. NCS/EMG revealed left median nerve demyelinating and axon loss compression neuropathy across the carpal tunnel involving both motor and sensory fibers, consistent with left mild-moderate carpal tunnel syndrome. Diagnostic ultrasound was recommended for further evaluation due to nondominant hand with CTS.
Discussions: Veteran was lost to follow-up however, was seen by Hand/Plastics seventeen months later with new left grip strength weakness. Imaging was recommended and referral to PM&R clinic for diagnostic ultrasound was placed. On ultrasound, median nerve was found to have infiltrative mostly circular, well circumscribed, with partial loculations and intratumoral cystic mass distally. Flexor digitorum profundus was medially located due to mass effect however was normal appearing without infiltration from the distal forearm through the carpal tunnel. Findings were suggestive of plexiform schwannoma vs neurofibroma. MRI was ordered revealing lobulated mass like hyperintensity along the median nerve suggestive of plexiform neurofibromas or schwannomas. Biopsy for identification of the mass were recommended for potential surgical planning.
Conclusions: While schwannomas do not become malignant, plexiform neurofibromas may become malignant peripheral nerve sheath tumor (MPNST) in up to 15% of cases. MPNST is aggressive and carries a poor prognosis. This is an interesting case demonstrating that routine carpal tunnel doesn’t always indicate median nerve compression at the carpal tunnel. Rather here, given the carpal tunnel was presenting in a nondominant hand and absent in the dominant hand, warrants further physiatriac work up. This demonstrates the value of diagnostic ultrasonography in “zebra” diagnoses when combined with physical examination and clinical judgement.
