UNILATERAL SPASM OF THE MASSETER MUSCLE - A SUBTYPE OF MASTICATORY HEMISPASM - CLINICAL AND ELECTROPHYSIOLOGICAL FINDINGS IN A PATIENT

We describe the clinical and electrophysiological findings in a 26-yea rs-old male patient, who suffers from sudden cramps in his right masse ter muscle since the age of fourteen. The cramps rarely occure spontan eously but are mostly triggered by innervation during speach or chewin g. The cramps can always be interrupted by forceful opening of the mou th. The symptom is restricted to the right masseter muscle clinically and electromyographically. The masseter reflex could not be elicited o n the affected side. The silent periods 1 and 2 of the masseter inhibi tory reflex on the affected side were not abolished shortly after the beginning of the cramps but disappeared within some seconds during the cramp. Cranial MRI showed no abnormalities. We conclude that the corr ect diagnosis is hemimasticatory spasm involving only the right masset er muscle. Other possible diagnoses such as unilateral oromandibular d ystonia, hypertrophic branchial myopathy, local tetanus or symptomatic dysfunction of the brainstem were excluded by the clinical and neurop hysiological findings in our case. Therapy with botulinum toxin type A was followed by symptomatic relief lasting for about 4 months.