Sporotrichosis mimicking necrotising arachnidism

A 31-year-old woman was picking mandarins near Bindoon, Western Australia, when she felt something bite her wrist. When she looked, she saw a large hairy spider. A red lesion developed immediately and failed to resolve after a week, so she attended her general practitioner (A R N), who prescribed roxithromycin. After a further week she developed a 30 mm diameter, full-thickness ulcer on her wrist with some lymphangitis (Figure, above). At this point she attended an after-hours clinic, where wound care and an occlusive dressing were provided. After another three weeks she returned to her GP with no improvement, and nodular lymphangitis. Pus was aspirated from a fluctuant nodule and sent for culture. Therapy with doxycycline was started. The gram stain of the aspirate showed numerous pus cells, but no organisms. The culture showed no growth after two days, but was kept for extended incubation. The working diagnosis was necrotising arachnidism. After a further week the patient was referred to plastic surgeons at a public teaching hospital, where she was admitted and treated with intravenous clindamycin. She was discharged home with little improvement.

Meanwhile, after 10 days' incubation, the aspirate culture plates grew a yeast-like organism, which was subcultured onto cornmeal agar for slide culture at 25C. Microscopy showed a mould form of the organism, with clusters of ovoid, denticulate conidia produced sympodially on short conidiophores. With time at 25C, the colony became blackened, glabrous and developed a wrinkled surface. This characteristic microscopy and thermal dimorphism confirmed the organism's identity as Sporothrix schenckii -- the agent of sporotrichosis. The patient has since been prescribed itraconazole and her condition is rapidly improving. Although our patient had lymphocutaneous sporotrichosis, there is also a fixed cutaneous form without lymphangitis.³

While there are reports of sporotrichosis associated with a variety of bites, including insects,^4,5 we believe that this is the first report associated with a possible spider bite. We think it is important that in cases like this good quality specimens be sent for microbiological analysis and that they be specifically cultured for mycobacteria and fungi, or at least incubated for an extended period, before necrotising arachnidism -- the diagnosis of exclusion -- is diagnosed.

Len D Moaven
Clinical Microbiologist, St John of God Pathology
Wembley, WA
(moavenATbigpond.com.au)

Shelley A Altman
Senior Scientist, St John of God Pathology
Wembley, WA

A Richard Newnham
General Practitioner
Bindoon, WA

1. Pincus SJ, Winkel KD, Hawdon GM, et al. Acute and recurrent skin ulceration after spider bite. Med J Aust 1999; 171: 99-102.
2. White J. Necrotising arachnidism. Med J Aust 1999; 171: 98.
3. Auld JC, Beardmore GL. Sporotrichosis in Queensland: a review of 137 cases at the Royal Brisbane Hospital. Aust J Dermatol 1979; 20: 14-22.
4. Vismer HF, Hull PR. Prevalence, epidemiology and geographical distribution of Sporothrix schenckii infections in Gauteng, South Africa. Mycopathologia 1997; 137: 137-143.
5. Lober C, Kaplan R, Herron C. Sporothrix schenckii inoculation on the abdomen. South Med J 1980; 73: 1637-1638.

©MJA 1999
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