Teaching Video NeuroImage: Delayed Radiation-Induced Unilateral Myokymia of the Tongue

A 49-year-old man with undifferentiated nasopharyngeal carcinoma underwent 2 cycles of chemotherapy, followed by right-side head and neck radiation therapy. Thirteen years later, he developed progressive dysphagia and dysarthria. Neurologic examination showed atrophy associated with wave-like movements and prominent rippling in the right side of the tongue; needle electromyography revealed myokymic discharges in the right genioglossus muscle (Video 1). MRI of the head and neck confirmed isolated unilateral tongue atrophy (Figure) while laryngoscopy showed delayed initiation of swallowing and reduced laryngeal elevation.Delayed effects of radiation therapy could be seen even decades later and are directly related to radiation dosage.(1) Myokymic discharges of the tongue are likely due to the damage of the hypoglossal nerve induced by microvascular injury and fibrosis with subsequent hyperexcitability of the axon membrane.(1) In an oncology patient, myokymia is usually associated with radiation-induced neuropathy rather than cancer recurrence.(2)