The tertiary stage can manifest as rheumatologic, neurologic, and/or cardiovascular.
Rheumatologic manifestations are the most common late manifestations and joint involvement is usually seen in the lower extremities. 60% of those untreated 20 years ago developed joint swelling. Today, it is only 10% because diagnosis and antimicrobial therapy is provided earlier in the primary stage. 90% of Lyme arthritis is in the knee and migratory transient intermittent arthritis and effusions may occur. The synovial fluid usually demonstrates about 24,000/mL WBCs with granulocytes predominating. Pain in muscles, bones, tendons, and bursa is frequently experienced. A Baker's cyst may form behind the knee.
Neurological manifestations include cognitive difficulties with memory, mood, and sleep disturbances. These manifestations are uncommon. Encephalomyelitis is parenchymal inflammation of the brain and/or spinal cord. In this condition, the CSF demonstrates a lymphocytosis, moderately elevated protein, and normal glucose. Peripheral neuropathy is intermittent and may show decreased vibratory sensation of the legs and feet. Encephalopathy affects memory and cognitive impairment, but in this manifestation, the CSF is normal.
Cardiovascular manifestations, although also rare, can be serious and lead to death. Only 5% develop cardiac involvement. Conduction abnormalities, such as atro-ventricular node blocks, may occur. Myocarditis and pericarditis have been reported.