Lyme borreliosis (LB) is a tick-borne zoonosis caused by spirochetes belonging to the Borrelia burgdorferi sensu lato (Bb sl) complex. In Europe, multiple pathogenic species—including B. afzelii , B. garinii , and B. burgdorferi sensu stricto—are responsible for a wide diversity of clinical manifestations. The disease may present in various stages—localized, early disseminated, or late disseminated—depending on the time elapsed since the tick bite and the organs involved, such as the skin, joints, or nervous system.

Erythema migrans (EM) is the most frequent clinical presentation, accounting for approximately 80 % of LB cases in France. It is an early localized form, characterized by a painless, centrifugally expanding erythematous lesion centered on the tick-bite site, typically appearing 3 to 30 days post-exposure and resolving within 15 days under antibiotic therapy. Neuroborreliosis (NBL), most commonly associated with B. garinii , occurs in approximately 6–15 % of French cases. It represents a disseminated form, often presenting as meningoradiculitis or peripheral facial palsy, with generally favorable outcomes under antibiotic treatment, although persistent post-infectious symptoms may occur.

These guidelines address the full clinical spectrum of LB, from common manifestations such as EM to rare complications involving cardiac or ophthalmological systems. They also encompass atypical presentations not specifically linked to LB and provide specific recommendations for special populations, including pregnant women and immunocompromised patients. The current section summarizes the principal clinical features of LB and supports the rationale underlying recent diagnostic and therapeutic recommendations.