clinical characteristics of eosinophilic synovitis
• Many have a history of atopy; some have dermatographism.
• Both sexes, age of onset 20 to 50 years. Can occur in childhood.
• Minor trauma causes acute onset (within 12–24 hours) of painless monoarthritis (usually knee) without warmth or erythema. Trauma may activate mast cells which attract eosinophils.
• Synovial fluid shows mildly inflammatory fluid with up to 50% eosinophils. Charcot–Leyden crystals (bipyramidal, hexagonal-shaped crystal made of products of intracellular lipases in eosinophils) may be seen.
• Peripheral blood WBC count normal. Peripheral blood eosinophilia in only 10%. Most have a normal ESR.
• Attacks last 1 to 2 weeks. Can have recurrences. Therapy includes NSAIDs.