A 35-year-old who has recently returned from an early summer fishing vacation in rural
North Carolina presents with a febrile illness. He reports a 5-day history of fever, malaise, headache, and vomiting. Today, he has developed a nonpruritic rash that began on his extremities and has spread to his body.
On exam he has a fever of 38.3◦C with a pulse of 120 and otherwise normal vitals. The rash is maculopapular and generalized, involving his palms and soles. Oral mucosa is dry but intact, and the exam is otherwise nonspecific.
Basic investigations were done and CBC shows mild thrombocytopenia but is normal otherwise. BUN and creatinine are at the upper limits of normal, and the electrolytes are normal.
The rash on his hand and feet is shown below:
What is the most likely Diagnosis?
Rocky Mountain spotted fever (RMSF).
Rocky Mountain spotted fever RMSF is a tick-borne (dog or wood tick) disease caused by Rickettsia rickettsii. Despite its name, RMSF is endemic in the southeastern United States, the Atlantic states, and the northern Rocky Mountains.
Clinical features: It presents with a prodrome of fever and headache several days before the onset of the characteristic rash—a maculopapular eruption that begins at the wrists and ankles and spreads centrally. Eventually, the rash becomes petechial.
Laboratory manifestations of RMSF are generally nonspecific: mild thrombocytopenia (rarely becoming severe), hyponatremia, azotemia, elevated transaminases, and prolonged PTT and PT.
Management: Early treatment is essential. Individuals treated after 5 days of symptoms have worse outcomes than those treated earlier. Awaiting serologic studies is inappropriate and treatment should not be delayed. The drug of choice in the treatment of RMSF is doxycycline 100 mg PO BID for 14 days.
This is true for children as well! Pregnant women should be treated with chloramphenicol. Agents such as penicillin, fluoroquinolones, and cephalosporins are inappropriate in this situation.