Clinical and electromyographic features of radiation-induced lower cranial neuropathy

Objective: Lower cranial neuropathy is a rare complication of radiation therapy for head and neck cancers. Little is known about the clinical and electromyographic features of this complication. Methods: The records of six patients with radiation-induced lower cranial neuropathy who had undergone electromyographic study were reviewed. All patients were treated with radiation therapy for nasopharyngeal cancer. The total radiation dose was 6996-8280. cGy to the nasopharynx and 4680-7020. cGy to the neck. The dose per fraction was 180 or 212. cGy. Results: Spinal accessory neuropathy occurred in all six patients, glossopharyngeal and vagus neuropathy in five patients, and hypoglossal neuropathy in five patients. The median latency between radiation therapy and lower cranial neuropathy was 61. months (range, 20-118. months). The lower cranial neuropathies developed insidiously and progressed slowly over a period of years in all patients. Myokymia was seen in three patients and myokymic discharges were demonstrated in five of six patients. Conclusions: Myokymia and myokymic discharges may be common and typical features of radiation-induced lower cranial neuropathy. Significance: It is important to make an effort to detect myokymia and myokymic discharges for symptomatic patients suggestive of radiation-induced lower cranial neuropathy.