Painful trigeminal neuropathy: clinical and pharmacological observations

A 74-year-old woman had a 5-year history of constant burning pain and numbness of the central face of subacute onset. The central region of the face, oral cavity, and nose lacked all sensation. Corneal reflexes and the jaw jerk were absent. Blood tests, rectal biopsy, neurodiagnostic studies, and surgical exploration of the trigeminal nerve were normal. Blink reflexes were absent. Facial nerve motor latencies and EMG of the facial and masseter muscles were normal. Responses to the thermoregulatory sweat test, intradermal histamine, and simulated diving were present. Oral administration of 500 mg L-dopa aggravated her pain and produced transient hypalgesia in the C2 through C6 dermatomes. Infraorbital nerve biopsy demonstrated loss of large myelinated fibers.

(1) Only the central region of the face is exclusively supplied by the trigeminal nerves. (2) Somato-autonomic reflexes coupled with electrophysiological studies localized the lesion to the large fibers. (3) Large fiber loss and central brain stem reorganization may explain the burning pain. (4) Dopamine may modulate trigeminal nociception.