Eosinophilic synovitis: clinical observations on a newly recognized subset of patients with dermatographism.

Eosinophilia of synovial fluid is uncommon. Using the identification of Charcot-Leyden crystals to alert for the presence of eosinophils, we have increased by a factor of 5 the detection rate of synovial fluid eosinophilia. We describe here our clinical and laboratory findings in 7 patients with this feature. We believe they constitute a defined syndrome. Typically, the patients were young (ages 18-51) and had a personal and family history of allergy. They developed an acute, painless monarthritis after a minor trauma, and had no concurrent allergic symptoms. Each episode resolved in 1-2 weeks without therapy, and 3 patients had recurrences. All had pronounced dermatographism. The synovial fluid was mildly inflammatory: 10,850 +/- 3,665 white blood cells/mm3, with 41 +/- 5% eosinophils (mean +/- SEM). The cellularity and chemistry of the peripheral blood was unremarkable, except for a mild elevation of IgE levels (370 +/- 104 IU/ml). The exact pathophysiologic mechanism underlying this benign entity is not clear, but we suspect a nonimmunologic triggering event is operant, i.e., synovial trauma which mimics the cutaneous dermatographism.