On May 26, 2009, a previously healthy man aged 51 years with no travel history outside of Montana went to a local emergency department immediately following onset of fever, severe acute frontal headache, dizziness, left-sided numbness, and tingling. No other symptoms were noted. Results of a physical examination were normal, except for an elevated blood pressure of 214/119 mmHg. Blood chemistries and cardiac enzyme tests were within normal limits, except for an elevated glucose of 130 mg/dL (normal: 70-110 mg/dL). Results of an electrocardiogram, magnetic resonance imaging, and computed tomography scan of the brain were normal. Oxygen was administered to the patient, telmisartan was prescribed for hypertension, and he was sent home. A week later, on June 2, the patient visited his primary-care physician complaining of fever, persistent headache, and new onset of muscle pain and weakness. The physician considered the patient's symptoms to be consistent with a neurologic illness and evaluated the patient further for a possible stroke or arboviral infection. A carotid Doppler test showed no evidence of abnormal arterial blood flow. A lumbar puncture performed on June 11 showed clear, colorless cerebrospinal fluid with no leukocytes or erythrocytes, and bacterial culture showed no growth at 72 hours; no tests for virus were performed. The patient was referred to and visited a neurologist on July 6. The neurologist found no evidence of stroke, diagnosed a complex migraine, and prescribed medication for headache management. The patient's symptoms gradually improved, and he reported no residual symptoms 6 months after illness onset.