Purpose: To report a rare case of painful trigeminal neuropathy after lateral medullary infarct and probe its underlying pathogenesis on the basis of neuroimaging and electrophysiological study.
Case report: A 45-year-old man presented acute onset of unsteady gait followed by paroxysmal and electric shock-like headache in the distribution of ophthalmic branch of left trigeminal nerve in 2 days. Neurological examinations showed hypoesthesia in the distribution of mandibular branch of left trigeminal nerve and left appendicular ataxia. Muscle powers and deep tendon reflexes were normal. Brain magnetic resonance imaging revealed infarct within the left cerebellum and middle portion of dorsolateral medulla. Vascular compression at the root entry zone of trigeminal nerve was excluded. Painful trigeminal neuropathy secondary to lateral medullary infarct was diagnosed. Ancillary blink reflex study 3 days after the stroke event showed abnormal late responses (R2), either ipsilateral or contralateral, after stimulation of left supraorbital nerve, suggesting left medullary lesion. Followup study 3 weeks later demonstrated normalization in absolute latencies of bilateral late responses, in line with remission of pain paroxysms on low-dose gabapentin treatment.
Conclusion: Painful trigeminal neuropathy attributed to lateral medullary infarct is a unique disease entity. Ophthalmic branch involvement, coexisting sensory deficits, absence of triggers, and rapid evolvement and remission are its characteristics. Our neuroimaging study delineated ischemic stroke pathology within descending tract and spinal nucleus of trigeminal nerve. Serial electrophysiological studies provide evidences supporting ephaptic transmission as the main pathogenesis concordant with dynamics of neuropathic pain and therapeutic implications.