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Fig. 36.1. The geographic distribution of tropical ulcer

Geographic Distribution

Patients with tropical ulcers are found in almost all tropical and subtropical regions of the world and those so afflicted may travel beyond the tropics (Fig. 36.1). These ulcers are probably most common in tropical Africa: in some regions, particularly Nigeria and Uganda, up to 30% of all new hospital patients may have had a tropical ulcer, judging by the scars and history. They are a common cause of skin cancer in parts of the Democratic Republic of Congo, West Africa, and Uganda, and among the Bantu of southern Africa. Tropical ulcers account for more than half of all the skin cancers in Sri Lanka, Indonesia, Java, Papua-New Guinea, the Pacific Islands, and Madagascar. They are also found throughout Asia and India, as well as South and Central America. Fortunately, for a variety of reasons, these ulcers are slowly becoming less common.

Etiology and Pathology

Careful research in Uganda has clarified the etiology. The ulcers occur at all ages, being recorded from age 5 to 70 years old. In children the sex incidence is equal, but in adults in most countries they are more common in men; this reflects the higher probability of trauma to the male leg. Ninety percent develop below the knee, affecting the front and outer side of the leg and the ankle region particularly. A minority develop in the thigh. All start with relatively minor injury to the skin; a large wound practically never develops into a tropical ulcer. Small cuts, bruises, abrasions from thorns, insect bites, and damage from grasses, stumps, and rocks when people walk through long grass are common etiological factors. The wounds are then contaminated either by flies, dirt, or the patient's saliva. Because wounds in the tropics are frequently dressed with local remedies, which may include cow dung, tobacco, or compresses of moss, infection is almost inevitable. If the wounds are washed routinely with soap and water, the incidence of tropical ulcer declines sharply.

Many published articles refer to malnutrition and chronic ill health as etiological factors. An association between the scars of tropical ulcer and hepatitis B has been reported. Nevertheless, the Uganda investigation clearly showed that these ulcers can develop in healthy people. Because malnutrition, vitamin deficiency, and chronic ill health are so common in the tropics (due not only to poor diet but also to multiple parasites), such factors undoubtedly contribute to the chronicity of these ulcers; but dirt is of far more importance etiologically and the causative bacteria are found in mud and water.

The histology is that of any chronic infection with considerable necrosis; eventually there is dense fibrosis surrounding the lesion. Thrombosis and vasculitis are not significant. The necrotic ulcers produce epithelial hyperplasia which can both clinically and histologically simulate squamous cell carcinoma. Malignant degeneration occurs in about 2%-9% of chronic tropical ulcers; it is rare before the age of 20. It may develop in as short a time as 3 years, but a 10 to 20-year history is more common and some patients survive 50 years before locally invasive lesions develop.

Laboratory Diagnosis

Although the exact cause of tropical ulcers may be disputed, they are associated with two organisms, Fusiformis fusiformis and Borrelia vincentii. These are common commensals in the mouth and faces, and have been found in more than 30% of tropical ulcers. The ulcers may be reproduced experimentally in man provided both these organisms are used together. Treponema vincentii has also been suspected.

B. fusiformis is a cigar-shaped, gram-negative organism, 5 to 12µm in length, with a straight or slightly curved axis. It is decolorized on Gram stain and is nonmotile; it has to be cultured anaerobically on serum agar or serum broth. Borrelia vincentii is a delicate organism, 5 to 10µm in length, with three to eight irregular spirals. It is motile, gram-negative, and stains with silver impregnation. It is best demonstrated by dark ground examination and also needs anaerobic culture on serum agar or broth. In experimental animals, no effect is produced by the injection of either organism alone, but when both organisms are injected together, infection occurs.

There are no other laboratory findings.

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