Neoplastic and paraneoplastic synovitis.

Arthritis is a common finding in patients who have cancer. In this population, it is crucial to rule out septic arthritis and metastatic synovitis. Culture, crystallography, (table see text) and cytology of synovial fluid are useful initial diagnostics tools. If all are negative, histopathology of synovial tissue should be considered. Crystal synovitis is another frequent cause of arthritis in patients who have cancer, but it can also coexist with other conditions such as septic arthritis. Independent rheumatic disorders, drug-induced arthritis, and paraneoplastic syndromes should be considered after the exclusion of sepsis and metastatic disease. The diagnosis of a paraneoplastic syndrome is easier when the malignancy is evident or typical findings such as HOA or palmar fasciitis are present. However, these paraneoplastic phenomena can occur before the cancer diagnosis, and it is important to be aware of the association of these conditions with an underlying tumor. Rheumatic disorders with atypical clinical presentation in older patients, poor response to usual treatment, systemic features such as weight loss, and clinical findings compatible with well recognized paraneoplastic syndromes should alert clinicians to the possible coexistence of an occult malignancy.