Differential diagnostic approach to paraneoplastic arthritis of the knee joint associated with rectal carcinoma

Paraneoplastic syndromes are associated with clinical, radiological or biological manifestations of malignancy without direct invasion of the tumour. The pathogenesis is unclear and different mechanisms have been implicated to explain the various manifestations induced by the cancer like deposition of immune complexes consisting of tumour antigens or production of hormones, immunoglobulins and cytokines. Articular symptoms associated with cancer are nonspecific and include various clinical manifestations. We present a very rare case of paraneoplastic arthritis associated with rectal carcinoma. Clinical characteristics of the disease as well as differential diagnostics are discussed. Recognition of certain musculoskeletal symptoms that may herald an underlying malignancy may allow for earlier diagnosis of a potentially curable malignancy and appropriate treatment of the arthritis. Proper differential diagnostic approach is of paramount importance in such cases. (authors)