An Isolated Trigeminal Sensory Neuropathy

A 60-year-old woman with no significant medical history presented to her neurologist with decreased sensation of the left cheek. Magnetic resonance imaging (MRI) with gadolinium contrast of the head, including the brain and cranial nerves, and magnetic resonance angiography of the head and neck were interpreted as normal. After a 2-year period of clinical stability, the sensory deficit gradually progressed to involve the entire left lower half of her face followed by the emergence of lancinating pain and allodynia over the same region. Neurologic examination confirmed a mild sensory deficit to light touch, temperature, and pin prick in the entire distribution of the second (V2) and third (V3) divisions of the left trigeminal nerve. She was started on carbamazepine with no relief. Subsequent MRIs of the head demonstrated abnormal thickening and enhancement throughout the entire left V2 nerve segment extending through Meckel cave and involving the cisternal portion of the left trigeminal nerve. In retrospect, the initial MRI demonstrated a small enhancing focus in the same region