To describe a case of West Nile Virus with atypical features including palatal tremor

While West Nile Virus (WNV) is the most common mosquito-borne illness in the US, less than 1% of cases are neuroinvasive. Neuroinvasive WNV typically presents with flaccid paralysis and/or encephalitis in immunocompromised individuals.

Hypertrophic olivary degeneration (HOD) is a hypertrophic, rather than atrophic, degeneration of the inferior olivary nucleus, often preceded by an insult- such as hemorrhage, infarct, or tumor- within the Guillain-Mollaret triangle. Patients classically present with palatal tremor, sometimes accompanied by dysarthria, ataxia, or opsoclonus.

An 84-year-old male with history of idiopathic pulmonary fibrosis presented with an abrupt decline in mental status requiring intubation, in the setting of weeks of progressive dysphagia, ataxia, and lower extremity weakness. He followed some commands with facial muscles but was plegic all extremities.  Lumbar puncture was significant for lymphocytic pleocytosis, normal glucose, and elevated protein. MRI brain revealed a nonenhancing T2 hyperintensity in the bilateral ventral medulla, including the inferior olivary nuclei.  Upon extubation, he was found to have palatal tremor, dysarthria, and dysphagia. CSF resulted positive for WNV IgM. Strength improved with 5 days of IVIg, though he remained ataxic on follow-up.

We describe a rare presentation of WNV causing medullary rhombencephalitis with features of hypertrophic olivary degeneration. There was initially concern for HOD due to MRI findings, palatal tremor, and progressive dysarthria, dysphagia, and ataxia. However, the patient’s abrupt change in mental status, face-sparing tetraplegia, and lymphocytic pleocytosis were more consistent with neuroinvasive WNV. Neuroinvasive WNV has been described to cause encephalitis, most commonly affecting the thalamus, midbrain, or pons; however, medullary involvement is less common and palatal tremor has not typically been described.