Fig. 37.1 Ainhum: clinical photograph shows the characteristic deep constricting groove in the plantar digital fold along the medial aspect of the fifth toe. Note the slight abduction of the toe and deformity of the toenail. (From Dr. W. W. Davey: Companion to Surgery in Africa. E & S Livingstone, London, 1968).

Fig. 37.2 Ainhum involving the fifth toe of a 45-year-old Mukongo man in the Democratic Republic of Congo. The constricting sulcus and the bulbous distal portion of the toe are seen, as well as medial rotation of the plantar surface of the toe. The toenail is on the lateral surface. AFIP 76-6672. (From. C.H. Binford and D.H. Connor, eds. Pathology of Tropical and Extraordinary Diseases. Armed Forces Institute of Pathology, Washington DC, 1976).

 

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Etiology and Pathology

Many etiologies have been proposed for this strange disease, but as yet none have been proven. Heredity, trauma, keloid formation and sickle cell disease have been exonerated. Infection seems to play little or no role initially, since histologically the early lesion is a noninflammatory constriction with no evidence of bacteria or fungi present. Ainhum is at times seen in association with such chronic infections as yaws, leprosy and tuberculosis, but there appears to be no definite etiologic relationship. Some investigators have thought that it might be a manifestation of the chronic fissuring seen in late yaws; for example, in the Democratic Republic of Congo there is a higher incidence of ainhum in patients with framboesial hyperkeratosis associated with late yaws than there is in the general population. Unfortunately for this theory, ainhum occurs where yaws is nonexistent. Others suggest that the cause of ainhum is rotational strain. There is often rotation of the affected toe and when ainhum occurs in a finger, which is rare, ankylosis of a joint or some other factor leading to abnormal rotation in the digit is usually present.

At present, the exact cause of ainhum remains a mystery, but two undisputed factors associated with its development are race and prolonged walking on bare feet. The fibroblastic diathesis or abnormal fibrogenesis commonly noted in the African, especially with regard to keloid formation, may be an associated factor. Mechanical rotational strain of the digit, recurrent chronic fissuring, and perhaps altered endarterial vascular supply or angiodysplasia may all play a vital role in its etiology. In a 1981 report by Dent et al from Cape Town, there was a consistently abnormal blood supply to the affected foot proximal to the groove at the plantar digital fold. The posterior tibial artery was narrowed at the ankle and there was absence of the plantar arterial arch and its branches. The dorsalis pedis artery with its arcuate branch and dorsal metatarsal branches constituted the only arterial supply to the forefoot and fifth toe. These South African investigators thought there might be a genetic cause for this vascular anomaly, since all patients were born in the Transkei, but they were unsure whether the anomaly represented the etiology of ainhum or was simply an associated finding.

The deep constricting groove, which is known as ainhum, begins in or distal to the plantar digital fold of a toe along its medial aspect (Figs. 37.1 and 37.2). The groove usually extends most rapidly towards the dorsum of the toe, with the result that the last portion of the skin to be involved is on the outer plantar surface. Initially the groove consists of altered condensed keratin laid down by abnormal cells in the prickle cell layer, and at this stage shows no evidence of bacterial or fungal infection, inflammation or fibrosis. As it spreads the groove becomes deeper and wider and eventually ulcerates medially where it began.

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