From the Guidelines
The histological findings of a spider bite can vary depending on the species, but typically include epidermal necrosis, dermal edema, and inflammatory cell infiltration, as seen in brown recluse spider bites which characteristically show a "hourglass" pattern of coagulative necrosis. The effects of spider bites can be severe and vary widely, with some species like the black widow and brown recluse causing more severe localized and systemic symptoms 1. Some key histological features of spider bites include:
- Epidermal necrosis
- Dermal edema
- Inflammatory cell infiltration
- Coagulative necrosis with a sharp demarcation between viable and necrotic tissue in brown recluse spider bites
- Neutrophilic infiltration and thrombosed vessels
- Vasculitis with fibrinoid necrosis of vessel walls
- Dense neutrophilic infiltrate with tissue destruction, hemorrhage, and sometimes a blue-gray discoloration of vessel walls due to hemosiderin deposition as the lesion evolves. Black widow spider bites, on the other hand, show less distinctive histopathology, with mild inflammation and occasional small vessel thrombosis 1. It's worth noting that diagnosis can be challenging as spider bite histology can mimic other conditions like pyoderma gangrenosum, vasculitis, or infection, and the presence of eosinophils is variable and not diagnostic 1. These histological features reflect the action of spider venoms, particularly sphingomyelinase D in brown recluse venom, which causes cell membrane disruption, complement activation, and subsequent tissue damage.
From the Research
Histological Findings of Spider Bites
The histological findings of spider bites, particularly those from the brown recluse spider, have been studied to understand the effects of envenomation on tissue.
- A mixed inflammatory cell infiltrate is a common finding, indicating the body's response to the venom 2.
- Coagulative tissue necrosis is also observed, which can lead to the formation of necrotic ulcers 2.
- Vasculitis, or inflammation of blood vessels, is another key finding, with small vessel vasculitis being a universal feature in one study 2.
- A well-delineated zone of eosinophilic staining, recognizable as "mummified" coagulative necrosis of the epidermis and dermis, is a characteristic feature of brown recluse spider envenomation 2.
- A dense band of neutrophils borders the zone of necrosis, and degranulated eosinophils and neutrophils and macrophages filled with eosinophilic granules are common 2.
Tissue Damage and Necrosis
The histological findings suggest that the venom from the brown recluse spider causes significant tissue damage and necrosis.
- Large vessel vasculitis, resembling that seen in polyarteritis nodosa, may contribute to the large zones of necrosis seen after some brown recluse spider bites 2.
- Eosinophils may play a role in tissue damage after envenomation, and their presence is a notable feature of the histological findings 2.
- The clinical consequences of spider bites can be severe, with necrotic ulcers and systemic symptoms being reported in some cases 3, 4, 5, 6.