Prominent Bullseye Rash of Lyme Disease

Description

Centered on the posterior trunk of an adult male, an annular erythema migrans lesion occupies the cutaneous surface of the back, with an outer erythematous rim and relative central clearing overlying the subcutaneous tissues of the thoracic region. The surrounding integument appears normal in color and texture, without obvious edema, vesiculation, or secondary excoriation. Relative to the midline, the lesion sits laterally on the dorsal skin and expands centrifugally within the dermis. Borders are the key visual cue. Erythema migrans remains the most useful early clinical sign of Lyme borreliosis (Borrelia spirochete infection after an Ixodes tick bite), and this morphology helps separate it from allergic arthropod reactions, cellulitis, tinea corporis, and the southern tick associated rash illness pattern that can mimic Lyme. Absence of a punctum does not exclude a tick bite, and many patients never recall the tick, so recognition of an enlarging annular plaque matters when triaging for early antimicrobial therapy to reduce risk of facial nerve palsy, meningoradiculitis, Lyme carditis with atrioventricular block, or later oligoarticular arthritis. The presentation here also reflects a common teaching point: the classic bullseye is variable, and erythema migrans can appear as a single expanding red patch without a sharply defined target center. Useful for infectious disease and dermatology teaching modules, primary care and urgent care reference materials, and patient education on tick-borne infection warning signs, this photograph also supports atlas content on cutaneous manifestations of systemic bacterial disease and differential diagnosis of annular erythema on the back. Anatomical accuracy verified by SciePro's Medical Advisory Board.