The surgical pathology of human Lyme disease. An enlarging picture.

Lyme disease is a multisystems infectious disorder caused by the spirochete, Borrelia burgdorferi. Infection occurs by ticks feeding on mammalian hosts, including humans. The distribution of the tick and spirochete is world-wide and is especially prevalent where there are large deer populations. The disease is seen in three stages. Stage I is a cutaneous rash (erythema chronicum migrans) consisting of lymphoplasmacytic infiltrates around dermal vessels. Stage II is characterized by varying forms of meningopolyradiculitis, with or without Bell's palsy or cardiac involvement (complete or incomplete heart block) and with interstitial endomyocarditis of lymphocytes and plasma cells. Lymphoplasmacellular infiltration is seen in the meninges, ganglia, and peripheral nerves. Chronic and intermittent oligoarthritis is the hallmark of stage III disease, characterized by hypertrophic synovitis, often with fibrinaceous deposits and synovial vascular occlusion. Stage III chronic dermatologic syndromes (lymphadenosis benigna cutis, acrodermatitis chronicum atrophicans) consist of cutaneous lymphoid hyperplasia and vascular changes. Neurologic demyelination syndromes also occur in stage III. Plasma cells occur in all stages, but are more prominent in stages II and III. Spirochetes can be demonstrated by silver impregnation stains in some cases.