A 32-year-old trekker presents 7 days after a tick bite with a single expanding annular erythematous plaque 9 cm across with partial central clearing on the thigh. He is otherwise well and afebrile. The most appropriate next step is:

• A Order ELISA followed by Western blot before starting therapy
• B Start intravenous ceftriaxone immediately
• C Reassure and review after 4 weeks since the lesion will resolve spontaneously
• D Treat empirically with doxycycline without serological testing ✓

Explanation

Erythema migrans is the hallmark of early localised Lyme disease and is sufficiently characteristic to permit clinical diagnosis. Antibody testing is insensitive in the first few weeks because specific IgM has not yet developed, so two-tier serology is recommended only for suspected disseminated or late disease, not for typical erythema migrans. Oral doxycycline for 10 to 14 days is standard for early disease without neurological or cardiac involvement. Intravenous ceftriaxone is reserved for meningitis, carditis or arthritis.

Reference: Harrison's Principles of Internal Medicine, 21st ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.