A 52-year-old woman comes to the office due to intermittent pain on the right side of the face for 3 weeks. The intense, sharp pain on the right cheek and lips lasts several seconds and recurs several times a day. The patient is afraid to brush her teeth or drink cold water because both trigger the pain. She is pain free between episodes. She has a history of hypertension, type 2 diabetes mellitus, and seasonal allergies. The patient does not use tobacco, alcohol, or illicit drugs. Temperature is 36.9 C (98.4 F), blood pressure is 136/84 mm Hg, and pulse is 80/min. No rash or facial asymmetry is noted. The remainder of the neurologic examination shows no abnormalities. Which of the following is the most likely cause of this patient's current condition?
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This patient with unilateral, intermittent sharp pain of the right cheek and lips that lasts several seconds and is triggered by minor stimuli (eg, brushing teeth, drinking cold water) likely has trigeminal neuralgia (TN). Characteristic clinical features of TN include the following:
The pathophysiology of TN is thought to be related to compression of the trigeminal nerve root as it enters the pons, leading to demyelination and atrophy of the nerve. Compression most commonly occurs due to a vascular loop, neoplastic growth, or multiple sclerosis plaque.
(Choice A) A demyelinating plaque (eg, multiple sclerosis) in the midbrain could impact cranial nerves that originate in the midbrain, including the oculomotor nerve (CN III) and the trochlear nerve (CN IV). However, CN V, which conveys sensation from the face, originates in the pons. A demyelinating plaque in the pons is one cause of TN.
(Choice B) A functional abnormality in the basal ganglia can lead to focal dystonia that can affect the face (eg, blepharospasm, oromandibular dystonia). Although pain can occur due to sustained muscle contraction and spasms can often be triggered or alleviated by sensory input (eg, "sensory trick"), severe neuropathic pain is uncommon with focal dystonia. In addition, this patient has no evidence of abnormal muscular contraction.
(Choice C) The pathogenesis of Bell palsy involves inflammation and edema of the facial nerve (CN VII). However, this usually does not cause pain but rather results in unilateral facial paralysis. In TN, compression of the nerve root leads to atrophy and demyelination rather than edema.
(Choice D) Herpetic neuralgia occurs due to reactivation of a virus (eg, herpes zoster); dermatomal pain can precede development of the classic vesicular rash by several days. However, seconds-long paroxysms of pain triggered by brushing teeth and unaccompanied by a rash after >1 week are more consistent with TN.
Educational objective:
Trigeminal neuralgia is caused by compression of the trigeminal nerve (CN V) root as it enters the pons, usually by an abnormal vessel loop. This leads to atrophy and demyelination of the nerve and causes short paroxysms of neuropathic pain.