Sympathetic or reflex footpad swelling due to crystal-induced inflammation in the opposite foot.

Sympathetic or reflex footpad swelling occurred in rats when several crystals known to be pathogenic in human joints or soft tissues were injected into the opposite footpad. Monosodium urate (MSU), calcium pyrophosphate dihydrate (CaPPD), hydroxyapatite, calcium oxalate (CaOx), and xanthine (X) suspension induced varying degrees of such reflex of sympathetic swelling. In the second cycle of crystal-induced swelling, the foot that had been the initial or primary site of inflammation reacted with greater reflex swelling, when compared to the first cycle. Similarly, reflex increases in temperature occurred when CaPPD was injected. These reflex increases in swelling and temperature may relate to signs and symptoms of patients with reflex neurovascular dystrophy or shoulder--hand syndrome.