High synovial immunoglobulin E levels in eosinophilic synovitis

Eosinophilic synovitis occurred in a 7-year-old boy. Synovial fluid leukocytes were mostly eosinophils; the peripheral blood showed only mild eosinophilia. The level of eosinophil-derived neurotoxin in the synovial fluid was higher than that in the serum, suggesting intraarticular eosinophil degranulation. The IgE level was also elevated in the synovial fluid (3854 ng/ml) but normal in the serum (408 ng/ml), suggesting a localized immediate hypersensitivity immune response.