Synovial fluid eosinophilia: a case series with a long follow-up and literature review

Objectives. To establish the frequency and describe the characteristics of a cohort of patients with SF eosinophilia (SFE) and a long clinical follow-up. A systematic review of the literature on this topic was performed. Methods. From November 2005 to May 2010, 982 consecutive arthrocentesis procedures performed at a tertiary care hospital were reviewed. Clinical and analytical data of patients with SFE at the time of diagnosis and during follow-up until 31 January 2012, were recorded. According to the percentage of eosinophils in SF, SFE was classified as minor (<10%) or major (>10%). Also, a literature search of all publications on eosinophilic synovitis found in MEDLINE, EMBASE and Web of Science without publication date restrictions was performed. Results. Eosinophils in SF were found in 10 of 982 (1.02%) patients: minor SFE was recorded in three patients, all of them with haemorrhagic fluid and without peripheral eosinophilia. Major SFE was found in seven patients, and only two of them had peripheral eosinophilia. In six patients, an underlying cause of the arthritis was found. Only one patient was classified as having idiopathic SFE. Most SFE promptly resolved with NSAIDs without relapses or new deformities. The literature search identified 56 patients with SFE; 49 of them (88%) had major SFE and 7 (12%) had minor SFE. Conclusions. Eosinophils are infrequently found in SF, and in most cases peripheral eosinophilia was not detected. Most patients with SFE had a benign course with prompt resolution and few relapses.