West Nile Encephalitis (WNE) is an arbovirus that is typically asymptomatic or self-limiting but can cause significant neurological sequela in immunocompromised hosts. This case highlights WNE presenting as opsoclonus-myoclonus syndrome which demonstrates the diagnostic difficulty encountered in immunocompromised patients. 

A young female with history of kidney transplant currently on immunosuppression, presented with diffuse abdominal pain, fever, and generalized malaise. Ten days later, she developed erratic eye movements and generalized hyperkinetic body movements. Over the course of one month, she progressed to flaccid paralysis. MRI imaging initially showed remote left MCA territory encephalomalacia from presumed traumatic brain injury. Initial CSF analysis was negative for infectious causes including WNE. She underwent multiple therapeutic interventions due to progressive decline in muscle strength and recieved methylprednisolone and IVIG. Repeat brain MRI showed T2 hyperintensity in the dorsal midbrain and pons. Spine MRI showed longitudinally extensive T2 hyperintensity within the ventral horn extending from the cervical spinal cord to the cauda equina and cervical, thoracic, and cauda equina nerve root enhancement. Repeat CSF testing showed serology positive for IgM antibodies against WNE virus. Ultimately, she was diagnosed with WNE. Her recovery course showed slow improvement in her extraocular movements and then motor strength, after which she was discharged to a rehab facility. Four months after discharge, she continued to improve and was able to ambulate with a walker.

This case report demonstrates that WNE can present with highly unusual initial symptoms, such as opsoclonus-myoclonus syndrome, which then progresses to more typical flaccid paralysis presentation later in the disease course. Additionally, diagnosing WNE can be even more challenging for immunocompromised patients, as their impaired immune system can delay confirmatory serological testing. Overall, this case report illustrates a unique diagnostic dilemma and important neuroimaging findings which can help clinicians in managing similar complex neurological presentations.