Winning Abstract from the 2007 Medical Student Abstract Competition: Mosquitoes, Meningitis, and Myocarditis: Another Etiology of Acute Febrile Illness.
Kate Pettit, Stanford University
West Nile Virus (WNV) is an increasingly common vector-borne illness. The general internist should be aware of thc cndemic areas for WNV, the multi-system nature of the presenting features of WNV, and the interpretation of diagnostic studies.
A 67-year-old male construction worker was admitted with myalgias, sore throat, cough, nausea, vomiting, non-bloody diarrhea, and rash for nine days. He denied sick contacts or recent travel, but did report mosquito exposure. He denied meningismus and photophobia. On admission, the patient had a temperature of 102.9 degrees Fahrenheit, heart rate of 96 bpm, respiratory rate of 22, and blood pressure of 115/65. Physical exam revealed dry mucous membranes and a faint erythematous maculopapular rash on the back, chest, and abdomen. Neurologic exam was within normal limits. Laboratory data was significant for an elevated serum WBC of 13,300/mm3 , elevated troponin of 0.08 ng/ml, and elevated creatine kinase of 405 u/l. Electrocardiogram showed elevated convex ST segments in leads V1-V3, new from prior ECG. Shortly after admission, the patient became somnolent and hypotensive. Emergent transthoracic echocardiogram showed a normal left ventricular ejection fraction (>55%) and no evidence of wall motion abnormalities. Cerebrospinal fluid analysis showed 190 WBC/mm3 with 68% neutrophils and 20% lymphocytes, glucose of 49 mg/dl and protein of 67 mg/dl. Empiric treatment with vancomycin, ceftriaxone, and azithromycin was initiated. Blood, urine, and CSF cultures were later negative. CSF EIA for WNV IgG and IgM was inconclusive. WNV serology was IgM positive by IFA and EIA. The patient received supportive care and was discharged with mild fatigue. Repeat ECG showed resolution of ST segment abnormalities and no pathological Q waves. Further cardiovascular investigation on follow-up concluded that the early electrocardiogram changes and increased troponins were likely secondary to perimyocarditis.
Infection with WNV is asymptomatic in approximately 80% of cases. Only 1 of 150 progress to neuroinvasive disease, with advanced age being the most important risk factor. Since the first cases in New York in 1999, WNV has rapidly become endemic in the U.S., with human cases in 43 of 50 states in 2005. The diagnosis should be considered in any patient with an acute febrile illness after mosquito exposure. The clinical presentation can include fatigue, headache, pharyngitis, gastrointestinal symptoms, rash, muscle weakness, meningitis, encephalitis, myocarditis, pancreatitis, and hepatitis. Serum and CSF assay for WNV IgM remains the most sensitive method of diagnosis, though IgM can persist for up to one year after acute infection. IgG avidity testing is a new method being studied to differentiate stages of infection.
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