Bilateral myoclonus of the trapezius muscles after distal lesion of an accessory nerve.

Observations of rhythmic or semirhythmic myoclonus due to a peripheral nerve lesion are exceptional. We report on a patient with thorax trauma with multiple bilateral hematomas of the paravertebral musculature. Eight years later he developed rhythmic myoclonus of both trapezius muscles and thoracic pain. Infiltration of a paramedially located scar at the level of D5-6 with a local anesthetic agent led to an intermittent relief of the myoclonus as did anesthetic blockade of the left accessory nerve. Surgical excision of the scar, which contained multiple dystrophic axons on histological examination, cured the patient's symptoms as illustrated in a videotape. This indicates that peripheral afferents contributed to the myoclonus. Ephaptic transmission, ectopic excitation, or misdirected neuronal sprouting secondary to the trauma are possible peripheral mechanisms responsible for the movement disorder. Successful blockade of the left accessory nerve with bilateral relief of the symptoms suggests a secondary, more centrally located mechanism, e.g., in the brain stem, probably driven by an altered afferent input. It is concluded that rhythmic or semirhythmic and focal myoclonus need a careful workup to look for a peripheral cause because such a condition would be accessible for surgical treatment.