A 34-year-old man comes to the physician due to high fever, malaise, and intermittent headaches for the last 4-5 days. He has no nausea, vomiting, abdominal pain, or neck stiffness. He recently returned from hiking for several days in wooded areas in Missouri. His past medical history is unremarkable.
The patient's temperature is 38.9 C (102 F), blood pressure is 118/78 mm Hg, pulse is 100/min, and respirations are 16/min. Physical examination shows a faint, non-pruritic, maculopapular rash confined to the trunk without central clearing. The remainder of the physical examination is unremarkable.
Laboratory results are as follows:

Which of the following is the most likely cause of his current condition?

Question

A 34-year-old man comes to the physician due to high fever, malaise, and intermittent headaches for the last 4-5 days.  He has no nausea, vomiting, abdominal pain, or neck stiffness.  He recently returned from hiking for several days in wooded areas in Missouri.  His past medical history is unremarkable.
The patient's temperature is 38.9 C (102 F), blood pressure is 118/78 mm Hg, pulse is 100/min, and respirations are 16/min.  Physical examination shows a faint, non-pruritic, maculopapular rash confined to the trunk without central clearing.  The remainder of the physical examination is unremarkable.
Laboratory results are as follows:

Which of the following is the most likely cause of his current condition?

Quizplus · Accepted Answer

11ec193a_984f_d97d_853d_5f007215e7cc_MD0002_00 Many tickborne diseases present with flu-like illnesses. However, this patient's presentation (high and prolonged high fever, leukopenia, mild thrombocytopenia, and rash confined to the trunk without central clearing) is suggestive of human monocytic ehrlichiosis (HME) caused by Ehrlichia chaffeensis and transmitted by the Amblyomma americanum (lone star) tick. HME typically occurs in the spring and summer months in the southeastern and south central United States. It is similar to human granulocytic anaplasmosis (HGA), another form of ehrlichiosis (seen primarily in the northeastern and midwestern United States and rarely associated with rash) that is transmitted by the Ixodes scapularis tick, which is also the vector for Lyme disease and babesiosis. Ehrlichiosis is usually suspected clinically. Peripheral blood smear may show the characteristic intracytoplasmic inclusions (morulae) in neutrophils. Indirect fluorescent antibody testing with antibodies specific to the organism is the preferred confirmatory test. Untreated HME patients can suffer serious complications (seizures, renal/respiratory failure) with increased morbidity and mortality. Patients should receive empiric doxycycline, which also treats Rocky Mountain spotted fever (often difficult to differentiate from HME or HGA in the early stages). (Choice A) Babesia microti causes babesiosis and presents with high fever, hemolytic anemia, and thrombocytopenia. However, rash and leukopenia are uncommon in babesiosis. A definitive diagnosis is made by finding parasitized red blood cells on thin blood smear. (Choice B) Lyme disease usually presents at the site of a tick bite with erythema migrans, which demonstrates central clearing and expands as the lesion progresses. However, leukopenia, high fever, and thrombocytopenia are uncommon in Lyme disease. (Choice C) Colorado tick fever is transmitted by the tick Dermacentor andersoni and occurs in the Rocky Mountain regions (western United States and Canada) at >4,000 feet elevation. Although this viral illness can present with similar symptoms, this patient's lack of travel history to the mountains makes this diagnosis unlikely. Most (>80%) patients with Colorado tick fever do not develop a rash. (Choice E) Rickettsia rickettsii causes Rocky Mountain spotted fever (RMSF) and can look similar in its early stages to HME, but leukopenia is less common in RMSF. In addition, the RMSF rash (seen in 90% of patients) usually begins on the extremities. Educational objective: Ehrlichial infection is commonly caused by Ehrlichia chaffeensis (human monocytic ehrlichiosis [HME]) and Anaplasma phagocytophilum (human granulocytic anaplasmosis [HGA]). Ehrlichiosis presents with severe and prolonged fever, leukopenia, and thrombocytopenia. Rash without central clearing is infrequent in HME and very rare in HGA. Doxycycline is the preferred treatment. __________ References: Current management of human granulocytic anaplasmosis, human monocytic ehrlichiosis and Ehrlichia ewingii ehrlichiosis (http://www.ncbi.nlm.nih.gov/pubmed/19681699) Human ehrlichiosis: a case study (http://www.ncbi.nlm.nih.gov/pubmed/19354021)

A 34-Year-Old Man Comes to the Physician Due to High