Examkin

Question

Difficulty: MediumInfectious Diseases

Following a week-long camping excursion in Rhode Island, a 34-year-old woman presents to an urgent care clinic with a 4-day history of sudden-onset high fever, profound fatigue, severe headache, and diffuse muscle pain. She has no significant past medical history and takes no medications. Her temperature is 38.9°C (102°F), blood pressure is 112/72 mmHg, and pulse is 98/min. Physical examination reveals no skin rashes, eschars, lymphadenopathy, or joint swelling. Sclerae are anicteric. Laboratory evaluation shows:

TestResult
Hemoglobin13.5 g/dL
Leukocyte count2,400/mm³
Platelet count78,000/mm³
Total bilirubin0.9 mg/dL
Aspartate aminotransferase (AST)115 U/L
Alanine aminotransferase (ALT)108 U/L

A peripheral blood smear is examined and reveals no intraerythrocytic inclusions. Which of the following is the most appropriate next step in management?

  1. Initiate oral doxycycline therapyAnswer
  2. B
    Initiate oral amoxicillin therapy
  3. C
    Initiate oral atovaquone and azithromycin therapy
  4. D
    Administer intravenous ceftriaxone
  5. E
    Order a tick-borne pathogen polymerase chain reaction panel and await results before treating

Answer

Initiate oral doxycycline therapy
The clinical presentation of acute fever, headache, and myalgias in a patient returning from a highly endemic area, combined with the classic laboratory triad of leukopenia, thrombocytopenia, and elevated transaminases, is highly suspicious for human granulocytic anaplasmosis. The absence of a rash makes Lyme disease less likely, and the absence of hemolytic anemia (normal hemoglobin and bilirubin) alongside a negative peripheral blood smear (no Maltese crosses or intraerythrocytic rings) effectively rules out babesiosis. Because anaplasmosis can progress to severe complications such as respiratory failure or toxic shock-like syndrome, empiric therapy with doxycycline must be initiated immediately upon clinical suspicion. Confirmatory testing (e.g., PCR or serology) should be ordered, but treatment must never be delayed while waiting for the results.

Step-by-Step Solution

1
Analyze the patient's exposure history and clinical presentation.
The patient has a history of tick exposure in an endemic area (Rhode Island) presenting with an acute febrile illness, severe myalgias, and headache without a rash.
Identifying the geographic and clinical context narrows the differential diagnosis to tick-borne illnesses such as Lyme disease, anaplasmosis, and babesiosis.
2
Evaluate the laboratory findings to differentiate between the potential tick-borne pathogens.
Labs show the classic triad of leukopenia, thrombocytopenia, and elevated transaminases. The absence of anemia, normal bilirubin, and negative blood smear make babesiosis highly unlikely.
This specific laboratory triad is the hallmark of human granulocytic anaplasmosis, caused by Anaplasma phagocytophilum.
3
Determine the most appropriate management based on the suspected diagnosis.
Empiric oral doxycycline is selected as the optimal initial step.
Anaplasmosis can cause severe complications if untreated. Therapy with doxycycline must be started based on clinical suspicion and not delayed for confirmatory testing.

Key Concept

Clinical presentation and empiric management of human granulocytic anaplasmosis
Rate this question

Topics

Infectious Diseases

More questions from this topic