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Lyme Disease — SCE Dermatology MCQ

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ModerateCutaneous InfectionLyme DiseaseSCE Dermatology

A 22-year-old woman presents with a 2 cm erythematous annular plaque with an atrophic centre on her arm. She had a tick bite 6 weeks ago. Borrelia serology is negative. Clinical suspicion for erythema migrans is high. Should treatment be withheld pending positive serology?

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Correct answer: D — No — treat empirically; serology is often negative in early Lyme disease and should not delay treatment

NICE NG95 explicitly states that erythema migrans is a clinical diagnosis and treatment should NOT be delayed awaiting serology. Borrelia serology is often negative in early disease — IgM antibodies may take 3-6 weeks to develop, and IgG even longer. Sensitivity of serology at the erythema migrans stage is only 20-50%. Empirical treatment with Doxycycline 100 mg BD for 21 days should be initiated based on clinical presentation and tick exposure history. Delaying treatment risks progression to disseminated disease (carditis, neurological involvement, arthritis). Two-tier serology (ELISA then immunoblot) is used for later-stage disease.

Reference: NICE NG95 2018 Lyme Disease; BAD