Various movement disorders in a patient with Sjögren syndrome

Geniospasm (OMIM 190100) is characterized by spontaneous repetitive involuntary contraction of mentalis muscles resulting in quivering or trembling of the chin that is intensified by stress or anxiety. The movements are first noticed in infancy or childhood and usually abate by late adulthood. Although geniospasm is a benign disorder the movements cause embarrassment and significant social anxiety. The nosology of the movements of geniospasm has been variously described as myokymia, tremor, and myoclonus but their origin remains unclear. 3 This report examines mentalis activity and facial nerve excitability in a patient with geniospasm. A 42-year-old man from a four generation Australian family with six affected members with geniospasm was studied. He had been aware of semicontinuous chin quivering since childhood. Neurological examination revealed bilateral continuous, semirhythmic chin quivering. There was no facial weakness. Drugs and left lower peripheral facial nerve surgery had no effect on the movements. Botulinum toxin (Botox, Allergan) injections (30 units in each mentalis muscle) every 8 to 10 months abolished the movements. Muscle activity was recorded from bilateral mentalis and orbicularis oculi (OO) muscles using needle and surface electrodes on a multichannel electromyography (EMG) system (Nicolet Viking III, Madison, WI). The supraorbital nerves (SON) were stimulated in the supraorbital groove at three to five times the sensory threshold and responses recorded from surface electrodes over both OO and mentalis muscles. Response latency was measured by visual inspection. Responses to facial nerve stimulation at the tragus were recorded in ipsilateral mentalis muscles. The mentalis muscle activity responsible for geniospasm comprised brief motor unit action potentials of normal morphology, 10 to 12 milliseconds duration and amplitude 50 to 100 lV, discharging arrhythmically at five to eight per second. Both sides were involved. There were no high frequency discharges or grouped discharges of myokymia. Voluntary contraction produced normal recruitment pattern that interrupted geniospasm. Stimulation of the facial nerves at the tragus evoked mentalis responses of normal morphology and latency (without late responses). Stimulation of the SON evoked a series of reflex responses in the facial muscles. Normal appearing blink reflexes (R1 and R2) were recorded from bilateral OO (not shown). Responses corresponding to R1, R2, and R3 were recorded from both mentalis (Fig. 1). Needle EMG confirmed the responses corresponding to the R2 and R3 were bilateral but R1 responses were more variable and largely unilateral (the anatomy of mentalis allowed surface EMG recording to pick up activity from both sides of the muscle). Spread of R2 responses beyond OO muscles is described in normal subjects with high stimulus intensities and in patients with synkinesis because of aberrant facial nerve regeneration. It is suggested in geniospasm spread of R2 and R3 responses to mentalis indicates facial nuclear hyperexcitability. The characteristics of geniospasm in this patient were similar to those described previously, 3 including spread of FIG. 1. Rectified surface EMG recordings from the mentalis muscles following stimulation of the supraorbital nerves (SON) (each trace represents the average of 10 trials). Unilateral SON stimulation evoked mentalis responses at latency 14 milliseconds corresponding to the R1 response of the blink reflex and bilateral responses at 42 milliseconds (corresponding to the R2 response of the blink reflex) and 90 milliseconds (corresponding to the R3 response of the blink reflex). The extent of facial muscle activity suggests facial nuclear hyperexcitability.