Histopathology of clinical phases of human Lyme disease.

Acute, subacute, or chronic persistent human Lyme borreliosis is an inflammatory disorder composed pathologically of lymphocytes, plasma cells, macrophages, and mast cells. The lymphoplasmocellular infiltrates can at times be seen in the skin, subcutaneous tissues, lymph nodes, spleen, liver, myocardium, brain, autonomic ganglia, and peripheral nerves. The joints in arthritic cases have proliferative synovitis, fibrinaceous deposits, lymphoplasmocellular aggregates, and mast cells. Varying degrees of vascular damage does occur in these sites; however, usually only in late, chronic disease. Spirochetes are present in most sites, in an extracellular location, but are sparse.