Orthostatic Jaw Tremor, a Diagnostic Challenge for Neurologists

Abstract

Jaw tremor is usually associated with tremor or other abnormal involuntary movements affecting additional body parts, but isolated jaw tremor is a rare clinical presentation. A 40-year-old man presented with history of paroxysmal jaw tremor for 3 years with no other neurological symptoms, psychiatric conditions, or a family history of neurological disorders. The tremor occurred only in the resting jaw position, with 10 episodes per day on an average, and lasted from 10 minutes to hours. It disappeared with any voluntary activation of the masseter muscle and did not change (in amplitude or frequency) with distraction maneuvers. The remainder of neurologic examination was unremarkable. The patient underwent extensive testing, including contrast-enhanced brain magnetic resonance imaging, blood tests and neuropsychiatric evaluation by two different neuropsychiatrists which failed to reveal the underlying cause. The needle electromyography examination revealed involuntary, intermittent, and synchronized muscular contractions in both masseter muscles, at a frequency of 13 to 14 Hz. No changes were discovered in the other muscles. He was treated with propranolol, primidone, valproic acid, diazepam, and amitriptyline, but the response was not significant. Injection of 25 units of botulinum toxin type A in the masseter muscle on both sides of the fac was effective five days after the injection. No adverse effects or masseter weakness were observed.