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A LJ6-year-old man with a h istory of non-Hodgkin lymphoma presents with myalgias. fever. and headache. Cen tral nervous symptoms worsened, and he became seriously ill and was admitted to the in tensive care unit for eval uation and treatment. Of note. the patien t stated he had been working in the woods and though t he may have had a tick bite. He last received treatment for lymphoma 2 years previously. Laboratory shows a leukocyte count of 3 ,200/pl, hemoglobi n 1 2 .3 g/dl, and platelet count LJ 7, 000/pl. An image from the peri pheral blood smear is shown below.
Rickettsial disease is suspected based on the patient's presentation and reported recent tick bites. Which of the following is the most likely diagnosis?
- Lyme disease
- Ehrlichiosis/anaplasmosis (HME/HGA)
- Rocky mountain spotted fever (RMSF)
- Tularemia
Medicine
B. The blood smear shows morulae in the cytoplasm of a leukocyte. This finding plus the patient's presentation of fever, myalgias, headache, leukopenia, and thrombocytopenia is consistent with a diagnosis of ehrlichiosis (human monocytic ehrlichiosis, caused by Ehrlichia chaffeensis, or human granulocytic anaplasmosis, caused by Anaplasma phagocytophilum). A diagnosis of ehrlichio-sis was made in the patient by serology immunofluorescence testing. Morulae are cytoplasmic mem-brane-bound vacuoles that contain hundreds of gram negative bacteria. Morulae may be detected in the peripheral blood smear in up to 50% to 80% of patients, especially in immunocompromised hosts. Ehrlichiosis is a tick-borne disease, with a clinical spectrum varying from a mild influenza-like illness to a fulminant sepsis syndrome with multiorgan failure. The presentations of these diseases overlap with other rickettsial conditions, but unlike Lyme disease and RMSF, characteristic intracytoplasmic inclusions are frequently found on the peripheral smear in HME/HGA.
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