2025 American Academy of Neurology Abstract Website

Objective:

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Background:

Isolated injuries to the posterior cutaneous nerve of the forearm (PCNF) are uncommon. To diagnose a neuropathy of the PCNF, an electrodiagnostic study (EDX) can be performed, but it is technically challenging. Here, we report a case of a PCNF neuroma-in-continuity in the forearm following a stabbing injury to highlight the importance of ultrasonographic evaluations for peripheral nerve traumatic injuries.

Design/Methods:

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Results:

A 65-year-old female presented to the clinic with numbness in her left hand and forearm, persisting since a stabbing incident nine months prior. The incident involved multiple stab wounds to multiple places, including three wounds to her left forearm. A referral was made for EDX, and the study was significant for incidental left chronic median neuropathy at the wrist. The PCNF was absent on the unaffected right side, likely due to technical issues, and therefore studying of the left side was not performed. Therefore, an injury to this nerve, corresponding to one of the stab wounds, could not be excluded. Subsequently, a NM US was performed. The study revealed a neuroma-in-continuity in the PCNF, with nerve enlargement proximal to the scar on the posterior mid-distal forearm.

Conclusions:

Using EDX to assess and the localize traumatic lesions is limited in the first 6 weeks, until reinnervation of the nerves begins. NM US has emerged as a tool in such scenarios, with the ability to demonstrate nerve edema, neuroma formation, or transection of the nerves, in cases of traumatic peripheral nerve injuries. Beyond the acute period, NM US is helpful in assessing for neuromas. This case demonstrates how NM US can detect abnormalities which are otherwise difficult or unable to be studied with EDX. These techniques are complimentary and assist the clinician in uncovering the underlying diagnosis when traditional EDX or imaging is unrevealing.