Trigeminal neuropathy commonly presents prolonged disorder of sensation in the distribution of the fifth cranial nerve of unilateral side and involves more than one division. We are reporting a case of a pure trigeminal motor neuropathy without sensory symptoms.

38-year-old man suffered from a mild common cold followed by progressive weakness and wasting of right masticatory muscles without pain or sensory change. Neurological examination revealed sunken cheek and temple area with weakness of the masticatory muscles and normal sensation of the face and normal taste. And all other cranial nerve were intact. Electrophysiological study revealed abnormal spontaneous activities with no voluntary motor unit potentials from the right temporalis and masseter muscles. The masseter reflex examination elicited by reflex hammer stimulation showed very small amplitudes from the right side. Trigeminal evoked potential, brainstem evoked potential and electrophysiological trigeminal blink reflex were normal. The imaging studies of the brain(CT and MRI) demonstrated atrophy of the right trigeminal motor nerve innervated muscles suggesting a pure trigeminal motor neuropathy without sensory involvement. We suspected a viral infection as the cause of their condition.