EMG is the most sensitive means of confirming a radiation induced plexopathy. The finding of myokymia is highly suggestive of radiation induced nerve injury. Sometimes SEPs are done to help evaluate the possibility of nerve injury but it rarely adds to the traditional EMG study and does not yield any unique information to help distinguish the cause of the nerve injury. Surgical exploration or a needle biopsy could be considered if tumor recurrence is clinically suspected. There is no effective treatment for radiation induced nerve injury.
Prognosis is guarded.
This case is a typical presentation for radiation induced plexopathy. The presentation of painless weakness years after radiation treatment with electrodiagnostic findings of myokymia is almost pathognomonic for radiation induced nerve injury. Although myokymic discharges can be seen in other chronic nerve injuries, it is quite rare and has not been reported associated with metastatic lesions. A significant consideration in the differential diagnosis is recurrence of the tumor. The clinical presentation of tumor recurrence varies but is much more likely to be associated with pain, and more sensory complaints than motor weakness.