Eosinophilic synovitis. A new entity?

The appearance and the biochemical, cytological and bacteriological findings were studied in synovial fluid obtained from the knees of 72 patients from south-west India. We report a group of 12 patients with 'eosinophilic synovitis'. In these patients, all below the age of 20 years with an acute onset of severe pain in the knee, there was a large effusion with painful limitation of movement. Their blood leucocyte count averaged 11,200 per mm3 with a mild eosinophilia of 6%. Biochemical examination of synovial fluid was normal, but cytology showed an increase in leucocytes ranging from 1200 to 20,500 (mean 9525) with between 75% and 90% of eosinophils in eight patients and 60% to 75% in four. All the patients responded well to a course of diethylcarbamazine.