Neuromuscular Choristoma Variant in the Forearm Presenting as a Posterior Interosseous Nerve Palsy: A Case Report.

CASE: A 14-year-old boy presented with an 18-month history of progressive left wrist drop. Magnetic resonance imaging studies were concerning for mass infiltration of the posterior interosseous nerve (PIN). Surgical resection and pathology confirmed a variant of neuromuscular choristoma (NMC), infiltrated with and surrounded by proliferation of smooth muscle, rather than skeletal muscle. Given the wide-spanning nerve involvement, the patient underwent tendon transfers at the time of surgical resection.

CONCLUSION

We report here the first case report of a NMC in the PIN and the first pathologically confirmed case with exclusive smooth muscle involvement without a skeletal muscle component.