You admit a 28-year-old man to the intensive care unit in July for a generalized tonic-clinic seizure in the setting of 2 days of fevers, headache, and myalgias. The patient’s girlfriend tells you that they were backpacking in Tennessee’s Great Smoky Mountains National Park the week before the patient became ill, and 3 weeks before he became ill they went for a hike in the woods on Massachusetts’ Cape Cod. Chest X-ray is clear, and his white blood cell count is normal. Platelet count on presentation is 139,000/µL, and hemoglobin and hematocrit are normal. Two days after admission, he develops worsening thrombocytopenia and a rash.
What is the MOST likely diagnosis?
A. BabesiosisCorrect Answer: B
RMSF (Answer B) is the most common tick-borne illness in the United States, with a broad distribution across most of the lower 48 states. Symptoms on presentation are often nonspecific. The classic rash (which often eventually involves palms and soles) is rarely present when the patient becomes ill and commonly develops 3 to 5 days into the course of illness. RMSF has an incubation period of 2 to 14 days after being bitten by an infected tick, and many patients do not recall any tick bite. Although Lyme disease (Answer D) can cause thrombocytopenia, confusion and seizures are not common with central nervous system Lyme disease; nor is late presentation of rash. Mumps (Answer C) often begins as a nonspecific illness of fever and malaise, but rarely presents with fever or seizures, and usually involved salivary gland swelling within 2 days of developing symptoms. Babesiosis (Answer A) is also a tick-borne disease that can be contracted on Massachusetts’ Cape Cod, but usually presents with anemia and does not cause seizures. Coinfections should always be considered when evaluating a patient with suspected tick-borne illness, as it is not uncommon for a single tick bite to transmit multiple infectious pathogens.
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