A 30-year-old trekker returns from Himachal Pradesh with an expanding annular erythematous plaque 8 cm in diameter with partial central clearing on his calf, noted 10 days after a tick bite. He is otherwise well with no fever or arthralgia. What is the appropriate next step?

• A Withhold treatment until two-tier serology becomes positive
• B Prescribe amoxicillin only if Borrelia-specific IgM appears on repeat testing after 6 weeks
• C Biopsy the leading edge of the lesion for Warthin-Starry staining
• D Treat empirically with doxycycline based on the clinical diagnosis of erythema migrans ✓

Explanation

Erythema migrans, the hallmark of early localised Lyme disease, appears about 7 to 14 days after the tick bite as an expanding erythematous plaque, often with central clearing. Diagnosis at this stage is entirely clinical because antibody titres have not yet risen and serology is frequently falsely negative in the first weeks; waiting for seroconversion risks progression to disseminated disease. Doxycycline is standard adult therapy, and biopsy is never required for typical lesions.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.