Atypical CSF findings in West Nile neuroinvasive disease: A diagnostic and therapeutic conundrum

Case report. A 59-year-old man presented in August 2012 with fever to 39.2°C, bifrontal headache, and 3 days of proximal left leg weakness without sensory complaints. He denied travel, lived in an urban setting, and reported no tick/mosquito bites. Neurologic examination was notable only for proximal left leg weakness and left leg areflexia. There was no rash or lymphadenopathy. EMG–nerve conduction studies (NCS) showed evidence of an acute left lumbosacral radiculopathy, anterior horn cell disease, and/or plexopathy (figure, F). Lumbar spine/lumbosacral plexus MRI revealed diffuse nerve root enhancement (figure, A–D). Brain MRI was normal. CSF analysis showed 163 nucleated cells/mL with 89% lymphocytes and 8% “atypical cells,” later designated plasma cells by a hematopathologist, and a protein of 147 mg/dL (figure, E). WNV antibody testing was sent while tests for other infectious etiologies (Gram stain, aerobic and fungal cultures, cryptococcal antigen, herpes simplex virus, varicella-zoster virus, cytomegalovirus, HIV, and tuberculosis) returned negative. Lyme serologies were not checked and empiric antimicrobial therapy was not initiated. Flow cytometry showed a small lambdapredominant CD191 B-cell population (0.3% of total cells). Further workup for lymphoma showed a serum lactate dehydrogenase of 253 IU/L (normal 100–250 IU/L); however, serum creatine kinase was 825 IU/L, suggesting a myogenic source. CSF on hospital day 12 once again showed a small population of CD19 B cells, this time negative for surface light chains. The second CSF sample showed a markedly elevated protein of 1,011 mg/dL with 9 nucleated cells/mL and a lymphocytic predominance (96%) (figure, E). Full-body PET/CT and additional workup for underlying inflammatory, neoplastic, or metabolic processes were unremarkable. Symptoms progressed, resulting in a flaccid left leg and new proximal right leg weakness. Repeat EMGNCS on hospital day 16 localized the lesion to the lumbosacral nerve roots and/or anterior horn cells (figure, F). At this point CSF testing for WNV was still pending. Although supportive care is the mainstay of therapy, a benefit of high-dose steroids in WNND has been reported. Given the progressive weakness with electrodiagnostic evidence of ongoing axon loss, he was started on empiric IV methylprednisolone. Nerve root biopsy was considered but never pursued given thatWNV antibody testing was still pending. WNV immunoglobulin M in CSF returned positive on hospital day 24 and steroids were discontinued. There was no change in the patient’s examination after steroids, and he developed no other sequelae ofWNND.At follow-up 8weeks later his examination was unchanged.