Histological findings after brown recluse spider envenomation

Histologic specimens from 41 rabbits were studied for changes resulting fro m the manual injection of brown recluse spider venom. Major findings includ ed a mixed inflammatory cell infiltrate, coagulative tissue necrosis, and v asculitis. All specimens demonstrated a well-delineated zone of eosinophili c staining recognizable as "mummified" coagulative necrosis of the epidermi s and dermis. A dense band of neutrophils bordered the zone of necrosis. Im mediately adjacent to the neutrophilic band, small vessel vasculitis was a universal finding. Degranulated eosinophils and neutrophils and macrophages filled with eosinophilic granules were common. Inflammatory foci were ofte n centered on groups of lipocytes within the dermis. Large vessel vasculiti s resembling that seen in polyarteritis nodosa was present deep to 7 of the 40 eschars. Large vessel vasculitis may contribute to the large zones of n ecrosis seen after some brown recluse spider bites. Eosinophils may play a role in tissue damage after envenomation.