Malignant joint effusions secondary to solid tumor metastasis.

We describe the case of a patient with breast cancer who developed bilateral malignant knee effusions, and review the English language literature. Patients with solid tumors who develop malignant joint effusions are rare; 27 cases have been reported (including our patient). The knee is the predominant site of joint involvement (p < 0.001). Synovial fluid (SF) analysis often demonstrates noninflammatory bloody effusion. Synovial biopsy was positive in 11 of 16 cases in which it was performed. SF cytology was positive in one half of cases in which it was obtained. Arthritis secondary to metastasis is a poor prognostic finding. A strong clinical suspicion is necessary to make the diagnosis; SF cytology or synovial biopsy can confirm it.