[A case of pure trigeminal motor neuropathy].

A 38-year-old man suffering from pure trigeminal motor neuropathy was admitted with a complaint of occipitalgia. Neurological examination showed severe wasting of the left masseter muscle on chewing. The jaw deviated to the left when he opened his mouth. Cerebrospinal fluid analysis was normal. The CT scan demonstrated a low density area in the left masseter, temporalis, lateral and medial pterygoid muscles. On MRI, the lesion of the left masseter, temporalis, lateral and medial pterygoid muscles showed high intensity of T1 and T2 weighted images. The cervical MRI revealed the non-communicating syringomyelia. Blink reflex, auditory brainstem response and trigeminal sensory evoked potentials were normal. EMG findings from the left masseter showed a neurogenic pattern. Muscle biopsy of the left temporal muscle demonstrated only fibroadipose tissue. Therefore, the present case was diagnosed as pure trigeminal motor neuropathy. It was suggested that multiple sclerosis might play an important role in the pathogenesis of this illness.