Necrotic arachnidism and white-tail spider bite
Necrotic arachnidism, or more commonly in Australia white-tail spider bite, has become an entrenched diagnosis despite the lack of evidence that spider bites cause necrosis or ulcers in Australia. In a prospective study of definite white-tail spider bites there were no cases of necrotic ulcers.
The bites caused pain in only 21% of patients, pain and a red mark for 24 hours in 35%, or a persistent red mark and associated itchiness, pain or lump lasting for about seven days in 44%. Current evidence suggests that spider bites are very unlikely to cause necrotic lesions and such cases presenting as suspected spider bites should be thoroughly investigated for other causes.
A recent series of suspected white-tail spider bites found other causes when appropriately investigated.
It is important to distinguish patients presenting with clinical effects (usually skin lesions or ulcers) that have been attributed to a spider bite and patients with a clear history of a definite spider bite.
Diagnosis and investigation in patients with ulcers must focus on important causes of necrotic ulceration including infectious, inflammatory, vascular and neoplastic conditions.