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Difficulty: EasyInfectious Diseases

A 28-year-old woman visits her primary care clinic due to a spreading rash on her right leg. She first noticed a small red bump four days ago, which has since expanded. The patient returned from a week-long camping trip in Connecticut ten days ago. She reports mild fatigue and muscle aches but denies fever, joint swelling, neck stiffness, or facial asymmetry. Her vital signs are within normal limits. Physical examination reveals a 9-cm erythematous annular plaque with central clearing on the right posterior calf. The lesion is flat, non-tender, and non-pruritic. Neurological and cardiovascular examinations are unremarkable. Which of the following is the most appropriate next step in management?

  1. Prescribe oral doxycyclineAnswer
  2. B
    Prescribe oral cephalexin
  3. C
    Prescribe intravenous ceftriaxone
  4. D
    Prescribe oral azithromycin
  5. E
    Prescribe topical clotrimazole

Answer

Prescribe oral doxycycline
The patient's clinical presentation of a large, expanding erythematous plaque with central clearing (erythema migrans) following outdoor activities in an endemic region (Connecticut) is pathognomonic for early localized Lyme disease. Caused by the spirochete Borrelia burgdorferi and transmitted by the Ixodes tick, early localized disease requires prompt empiric antibiotic therapy without waiting for serologic testing. Oral doxycycline is the treatment of choice for non-pregnant adults because it is highly effective and also treats potential coinfection with Anaplasma phagocytophilum.

Step-by-Step Solution

1
Identify the primary clinical finding and relevant patient history.
The patient has a large, expanding, flat annular rash with central clearing (erythema migrans) and recently camped in Connecticut (a highly endemic area for Lyme disease).
Recognizing the classic rash and endemic exposure establishes the clinical diagnosis of early localized Lyme disease.
2
Determine the need for diagnostic testing versus empiric treatment.
Erythema migrans is pathognomonic for early localized Lyme disease; serologic testing is not required and empiric treatment should be started immediately.
Antibody tests are often negative in the early stage of the disease, making clinical diagnosis paramount.
3
Select the most appropriate pharmacotherapy.
Oral doxycycline is the preferred first-line agent for non-pregnant adults.
Doxycycline effectively treats Borrelia burgdorferi and also provides coverage for Anaplasma phagocytophilum, a common coinfection transmitted by the same Ixodes tick.

Key Concept

Early localized Lyme disease is diagnosed clinically by the presence of erythema migrans in a patient with exposure to endemic areas, and it should be treated empirically with oral doxycycline.
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Topics

Infectious Diseases

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