It is convenient to divide the course and manifestations of Lyme disease (LD) into two stages: early (acute) and late (chronic).

In early LD, 80% of patients present with erythema migrans (EM). Most lesions are asymptomatic. Occasionally, the lesions burn or itch. EM is a highly characteristic skin lesion that first appears as a round or oval erythematous macule at the site of the tick bite (Fig. 18-1). A red punctum at the site of the tick attachment may be present at the center of the ring, the “bull’s-eye” in a circular target. The incubation period is 1 to 30 days, with an average of 9 days. Any area of the skin can be affected, and lesions can be single or multiple. The lesions expand nearly 1 cm per day to reach a diameter of 10 to 30 cm. Central clearing is common, giving lesions a ring-like configuration. Regional lymphadenitis may be present. Some patients also experience several days of chills, fever, headache, fatigue, and muscle and joint pain. EM clears spontaneously in a few weeks or months.

Late (chronic) manifestations of the infection appear weeks, months, or years after the tick bite and indicate dissemination of the infection. Intermittent arthritis affects the large joints, especially the knees. Central nervous system (CNS) involvement is common and consists of pain and weakness or numbness in arms or legs, fatigue, disturbances in vision, impaired hearing, facial paralysis (Bell’s), or the signs and symptoms of meningitis—headaches,
fever, stiff neck, and clouded sensorium. Cardiac involvement is less common and usually appears as a symptomatic variable atrioventricular block.