[A case of pure trigeminal motor neuropathy].

We reported a case of pure trigeminal motor neuropathy. A 57-year-old man was admitted with the complaints of vague headache and left upper limb numbness. Neurological examination showed mild wasting of the right masseter muscle on chewing. The jaw deviated to the right when he opened his mouth fully. Corneal reflex was intact bilaterally and so was the sensation on the face and taste. Mild hemiparesis including the face was observed on the left. Laboratory data including cerebrospinal fluid analysis were normal except for mild glucose intolerance. Blink reflex, brainstem auditory response and trigeminal sensory evoked potential elicited by electric stimulation of the lower lip were all normal. EMG findings obtained from the left masseter and lateral pterygoid muscles were neurogenic. The CT scan demonstrated a characteristically distributed low density area, which substituted the muscle supplied by the motor branch of he trigeminal nerve, namely, the right masseter, temporalis, lateral and medial pterygoid muscles. With MRI, the lesion was high on T1 and T2 weighted images. In addition, spotty high signal intensities suggestive of small infarction were observed in the bilateral centrum semiovale on T2 weighted images. Judging from the above results, the present case was believed to have pure motor trigeminal neuropathy confirmed by electrophysiological findings and image analyses together with clinical features. The mild left hemiparesis was thought to be incidental complication of vascular origin.