Case Presentation: A 39 year-old woman presented to our hospital in late August with non-neutropenic fever and a diffuse maculopapular rash involving her palms and soles. Past medical history was significant for HER2 positive, locally advanced inflammatory carcinoma of the breast. The patient had received neoadjuvant chemotherapy with adriamycin, cyclophosphamide, paclitaxel, pertuzumab, and trastuzumab two weeks prior to presentation. She had visited a nature preserve in Queens, New York three days prior to hospital admission, but did not recall being bitten by a mosquito. The patient’s initial physical exam was remarkable only for skin findings. Laboratory investigations including complete blood count, comprehensive blood count and coagulation studies were within normal limits. Early in the patient’s hospital course, she was empirically treated with doxycycline for a presumed rickettsial infection. On day three, the patient developed dysarthria, ocular flutter, and myoclonus of the right hand, suggestive of opsoclonus-myoclonus syndrome (OMS). Computed tomography of the head was significant for prominence of the pons. Pertinent cerebrospinal fluid (CSF) analysis demonstrated opening pressure 35 mmHg (normal 8-15 mmHg), 473 cells/µl (normal 0-8 cells/µl ) with 46% lymphocytes, protein 187 mg/dL (normal 15-45mg/dL), CSF glucose 60 mg/dL (normal 50-80 mg/dL), and negative gram stain. CSF analysis was most consistent with aseptic meningitis. West Nile Virus (WNV) reverse transcription-polymerase chain reaction was positive in the CSF. Serum immunoglobulins were checked and found to be unexpectedly low. The patient was treated with supportive management, including therapy with intravenous immunoglobulin and had a complete neurological recovery.

Discussion: This case highlights the importance of considering arthropod borne viruses in immunocompromised patients presenting initially with non-specific symptoms. WNV is the most common cause of epidemic meningoencephalitis and has the highest incidence in Summer and Fall months. While 80% of individuals with WNV remain asymptomatic 1% of patients can develop neuroinvasive disease. Elderly and immunocompromised patients are at highest risk of developing neuroinvasive disease. Morbilliform rash is a common initial finding, however, it seldom involves the palms and soles, as in our patient. Exanthems with such atypical distribution may raise suspicion for rickettsial or spirochete infection, obscuring a WNV diagnosis. WNV should be suspected in encephalopathic patients with movement disorders or flaccid paralysis. The pathogenesis of OMS is incompletely understood and could be attributed to basal ganglia involvement. Interestingly, OMS may be associated with hypogammaglobulinemia, as seen in the case of our patient. Rituximab has been associated with hypogammaglobulinemia, but other chemotherapeutic agents may also be implicated.

Conclusions: The clinical diagnosis of West Nile Virus can be challenging and its presentation can be atypical. West Nile Virus should be suspected in immunocompromised patients presenting with movement disorders or signs of brainstem encephalitis. We highlight a case of a patient, who developed opsoclonus-myoclonus syndrome secondary to encephalitis.