Unilateral black hairy tongue in trigeminal neuralgia.

Unilateral hairlike discoloration of the tongue is described in a patient with ipsilateral mandibular division trigeminal neuralgia. This unusual physical sign coincided with the patient's painful trigger zone and was attributed to hypertrophy of keratinized filiform papillae, where guarded avoidance of mechanical stimulation over time prevented normal desquamation.