Post-irradiation myokymia and neuromyotonia in unilateral tongue and mentalis muscles: report of a case.

We report a 52-year-old man with slowly progressive dysarthria and dysphagia for about 11 years after radiation therapy of nasopharyngeal carcinoma. Neurological examination revealed atrophy and myokymia on the left side of the tongue and in the left mentalis muscles. Electrical discharges of myokymia and neuromyotonia were also observed in the aforementioned muscles, suggesting increased motor axonal membrane excitability involving the left hypoglossal nerve and the marginal mendibular branch of the left facial nerve. Magnetic resonance imaging of the brain did not show any evidence of tumor recurrence, indicating that irradiation probably plays an important role in pathogenesis. Focal myokymia with concomitant neuromyotonia in unilateral tongue and mentalis muscles could be an unusual delayed manifestation after radiation therapy.