EARLY INFECTION, STAGE 1: LOCALIZED INFECTION
After an incubation period of 3-32 days, erythema migrans (EM) develops at the site of the tick bite in 80% of pts. The classic presentation is a red macule that expands slowly to form an annular lesion with a bright red outer border and central clearing; central erythema, induration, necrosis, or vesicular changes or many red rings within an outer ring are also possible.

EARLY INFECTION, STAGE 2: DISSEMINATED INFECTION

• Hematogenous spread occurs within days to weeks after infection. Secondary annular lesions may develop.
• Pts develop headache, mild neck stiffness, fever, chills, migratory musculoskeletal pain, arthralgias, malaise, and fatigue. These symptoms subside within a few weeks, even in untreated pts.
• Meningeal irritation: CSF is initially normal; however, weeks to months later, ~15% of pts progress to frank neurologic abnormalities (meningitis; encephalitis; cranial neuritis, including bilateral facial palsy; motor or sensory radiculoneuropathy; mononeuritis multiplex; ataxia; and myelitis).
• Cardiac involvement occurs in ~8% of pts. Atrioventricular (AV) block of fluctuating degree is most common, but acute myopericarditis is possible.

• Lyme arthritis develops in ~60% of untreated pts in the United States. It usually consists of intermittent attacks of oligoarticular arthritis in large joints (especially the knees) lasting weeks to months. Joint fluid cell counts range from 500 to 110,000/μL. Recurrent attacks decrease yearly, but a few pts have chronic arthritis with bony and cartilage erosion. Arthritis can persist despite eradication of spirochetes.
• Chronic neurologic involvement is less common. Encephalopathy affecting memory, mood, or sleep can be accompanied by axonal polyneuropathy manifested as either distal paresthesia or spinal radicular pain. In Europe, severe encephalomyelitis is seen with B. garinii infection.
• Acrodermatitis chronica atrophicans, a late skin manifestation, is seen in Europe and Asia and is associated with B. afzelii infection.