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Download the article PDF: Clinical Image Challenge December 2025
Differentia Diagnosis
- Eczema herpeticum
- Varicella
- Rickettsialpox
- Disseminated gonorrhea
- Cutaneous anthrax
- Mediterranean spotted fever
Diagnosis
Rickettsialpox is an uncommon mite-borne infection caused by Rickettsia akari, transmitted to humans by the painless bite of the house mouse mite (Liponyssoides sanguineus). It typically occurs in urban settings, with an incubation period of 10–14 days, and has been reported among individuals experiencing homelessness and those who inject drugs.
What to Look For
- Primary lesion: A 0.5–1 cm papule appears at the mite bite site, evolving into a vesicle with a violaceous or erythematous halo and forming a central black eschar (0.5–3 cm), resembling a cigarette burn.
- Systemic symptoms: Fever, headache, myalgia, and regional lymphadenopathy develop several days later. Photophobia, conjunctivitis, sore throat, and gastrointestinal symptoms may occur.
- Rash: A hallmark scattered papulovesicular eruption appears, with 2–10 mm lesions surrounded by erythematous halos that crust and heal without scarring. The rash often spares the palms and soles but may involve mucous membranes. Rarely, a cellulitis-like rash or absence of rash occurs.
- Laboratory findings: Early leukopenia with relative lymphocytosis is common. Mild hepatitis may occur and resolves with treatment.
- Skin tone variation: On darker skin tones, erythema may appear subtle, violaceous, or gray. Bright light may aid detection of color changes. Postinflammatory hyperpigmentation may persist longer than in lighter skin.
Pearls for Urgent Care Management
- Rickettsialpox is usually mild and self-limited, with symptoms lasting up to three weeks; early therapy may shorten illness duration.
- Diagnosis is clinical; biopsy confirmation is rarely feasible in urgent care.
- Treatment: Doxycycline 100 mg orally every 12 hours until afebrile for at least 48 hours (typically 5–7 days).
- Doxycycline remains the drug of choice for adults, children, and pregnant patients.
45-Year-Old Male With Arm Lesion, Headache, and Malaise
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