Speech-induced action myoclonus

Background: Speech-induced action myoclonus may occur as a component of a generalized myoclonus syndrome. However, it may also present in isolation, or with a paucity of other findings, and be diagnostically challenging. Objectives: To report a retrospective case series of restricted speech-induced action myoclonus. Methods: We reviewed cases of speech-induced action myoclonus evaluated at Mayo Clinic Rochester from 1989 to 2020. We eliminated cases where a more generalized myoclonic disorder was also present. Clinical, imaging, and electrophysiologic data were extracted. Results: Four cases were identified in which speech-induced action myoclonus of craniofacial muscles was the predominant clinical presentation. All described cranial muscle twitching induced by speaking, and two cases also reported speech interruptions. Diagnosis was confirmed by expert speech pathologists in all cases. Diagnostic aids included modulation with different speech tasks and speaking rates, and surface electrophysiology which confirmed craniofacial myoclonus induced by speaking tasks (three cases). Previous misdiagnosis included functional, dystonic, neuromuscular junction pathology, or hemifacial spasm. Two cases had isolated speech-induced myoclonus, and the other two had coexistent upper limb tremor. Potential etiologic factors were identified in three cases – medication (2), epilepsy (1) – while in one patient no cause was identified. One patient partially improved with anti-myoclonic medication and speech therapy. Conclusions: Speech-induced action myoclonus may occur in isolation and is frequently misdiagnosed. Diagnostic aids include modulation with different speech tasks and speaking rates, and surface electrophysiology.