Suspected white-tail spider bite and necrotic ulcers

To describe the clinical features, investigation, diagnosis and treatment of ulcers attributed to white-tail (WT) spider bites or necrotic arachnidism.

The study was a prospective case series of patients referred to the Hunter Area Toxicology Service (a tertiary referral toxicology unit servicing a population of 500 000) with an ulcer or skin lesion that had been attributed to either a suspected WT spider bite or necrotic arachnidism. Eleven patients with skin lesions or necrotic ulcers were referred between January 2000 and June 2002.

In two patients that were inpatients in other hospitals, investigation and follow up was not possible. In both cases there was no history of spider bite and Staphylococcus aureus was cultured. In nine patients, a diagnosis other than spider bite was made following appropriate investigation and follow up, including: (i) two cases of dermatophytoses, (ii) three staphylococcal infections, (iii) one case of pyoderma gangrenosum, (iv) one case of cutaneous polyarteritis nodosa, (v) one case of Nocardia braziliensis and (vi) one infected diabetic ulcer. There was only one case where the person recalled seeing a spider bite them, but the patient did not collect the spider for identification. The median time to diagnosis was 3 weeks (interquartile range: 3-9 weeks) and 3.5 years in one case. Appropriate treatment was initiated once the correct diagnosis was made and all cases resolved.

In this series, all cases initially referred as WT spider bites or necrotic arachnidism were found to have alternative diagnoses with appropriate investigations. This demonstrates that spider bites are an unlikely cause of necrotic ulcers and that all ulcers should be properly investigated with bacterial, fungal and mycobacterial cultures and skin biopsy for histopathology.