A 32-year-old man comes to the physician with a 2-day history of fever, headache, malaise, and myalgias. Family members say that he seems slightly confused. He recalls getting a tick bite 2 weeks ago while walking through the woods in Arkansas. His temperature is 39 C (102 F), blood pressure is 125/80 mm Hg, and pulse is 100/min. His neck is supple and there is no lymphadenopathy. The oropharynx is clear. Cardiovascular examination is unremarkable. The abdomen is soft and nontender. There is no rash. There are no focal neurologic deficits. Laboratory results are as follows: What is the most appropriate next step in management of this patient?

Question

A 32-year-old man comes to the physician with a 2-day history of fever, headache, malaise, and myalgias.  Family members say that he seems slightly confused.  He recalls getting a tick bite 2 weeks ago while walking through the woods in Arkansas.  His temperature is 39 C (102 F), blood pressure is 125/80 mm Hg, and pulse is 100/min.  His neck is supple and there is no lymphadenopathy.  The oropharynx is clear.  Cardiovascular examination is unremarkable.  The abdomen is soft and nontender.  There is no rash.  There are no focal neurologic deficits.  Laboratory results are as follows:  What is the most appropriate next step in management of this patient?

Quizplus · Accepted Answer

11ec25c8_d44b_3ca0_bc81_03ab1d56c28a_MD0003_00 This vignette depicts a patient with a typical case of ehrlichiosis. Ehrlichiosis is a tick-borne infection caused by Ehrlichia chaffeensis and E ewingii. These bacteria are carried by ticks, including the lone star tick (Amblyomma americanum), found in the southeastern and south central United States. The principal reservoir is the white tail deer. Ehrlichiosis is characterized by an acute febrile illness with malaise and altered mental status. Ehrlichiosis is not often associated with a rash (<30% in adults) and is described as "Rocky Mountain spotted fever (RMSF) without the spots." Neurologic symptoms may include confusion, mental status changes, clonus, and neck stiffness. Laboratory studies often show leukopenia and/or thrombocytopenia, along with elevated aminotransferases and lactate dehydrogenase. The diagnosis is often clinical, although definitive diagnosis can be made through visualization of intracytoplasmic morulae in white blood cells or through polymerase chain reaction testing. Doxycycline is the appropriate treatment and is often initiated empirically when the diagnosis is suspected while confirmatory testing is pending. (Choices A and F) Elevated liver enzymes and hematologic abnormalities, including leukopenia and thrombocytopenia, can be attributed to ehrlichiosis. As a result, hepatitis serologies and bone marrow biopsy would not be warranted. (Choices B and G) Ceftriaxone is used for the treatment of neurologic and cardiac manifestations of Lyme disease. Several factors make Lyme disease less likely in this patient. Ixodes scapularis, the tick that carries Borrelia burgdorferi, is not commonly found in the southern United States. The majority (80%) of patients with early localized (primary) Lyme disease (within days of the tick bite) have the classic erythema migrans rash with or without constitutional symptoms. The absence of a rash and the presence of a high fever and hematologic and liver enzyme abnormalities make Lyme disease less likely. Finally, this patient does not exhibit any prominent neurologic (eg, encephalitis, cranial nerve palsy, radiculopathy) or cardiac (eg, heart block, pericarditis) manifestations of early disseminated (secondary) Lyme disease. These would more commonly occur several weeks to months after the initial tick bite. Given the low suspicion for the disease, Lyme serologies would not be indicated. Even if this patient has Lyme disease, doxycycline would be sufficient to treat it. Lyme disease erythema migrans (Choice C) Chloramphenicol is a second-line treatment option for ehrlichiosis and RMSF. It is associated with blood dyscrasias and is not commonly used. In 90% of RMSF patients, a maculopapular rash (involving the soles and palms) occurs a few days after the onset of fever. The presence of leukopenia and absence of rash in this patient are more suggestive of ehrlichiosis than RMSF. Doxycycline is the first-line treatment. (Choice E) Erythromycin is not an effective treatment for ehrlichiosis. It has activity against Legionella and Mycoplasma. Educational objective: Ehrlichiosis should be suspected in a patient from an endemic region with a history of tick bite, febrile illness with systemic symptoms, leukopenia and/or thrombocytopenia, and elevated aminotransferases. Rash is uncommon, and the drug of choice is doxycycline. References: Tick-borne disease. (http://www.ncbi.nlm.nih.gov/pubmed/15999870) Tickborne infections in the southern United States. (http://www.ncbi.nlm.nih.gov/pubmed/20697259)

A 32-Year-Old Man Comes to the Physician with a 2-Day