Ainhum is the progressive constriction of the base of the fifth toe followed by spontaneous amputation. The disease is observed throughout Africa with varying frequency, in mulattos in the Antilles and South America and sporadically in other parts of the world. It is a disease of adults. The aetiology and pathogenesis have not been established yet. There is some hereditary predisposition and small wounds may play a role, together with the tendency to keloid formation. A groove first forms on the lower and internal side of the base of the small toe, which gradually becomes deeper and circular. The distal part of the toe swells and becomes round. The disease is for the most part not painful. After 10 years or more, the toe falls off or is amputated. The disease is often symmetrical on both feet (60%), but sometimes other toes are also affected and rarely also the distal phalanx of the fifth finger. Amputation is the only effective treatment, although local injection of corticosteroids into the fibrous band reduces the pain in the rare cases where this is necessary. Ainhum is easy to recognise clinically. A rare syndrome ("Vohwinkel syndrome" = keratoderma hereditaria mutilans or pseudo-ainhum) can resemble ainhum, but is characterised, in addition to ainhum-like constrictions of the distal phalanges, by diffuse hyperkeratosis of the palms of the hands and soles of the feet and "starfish-like" hyperkeratosis on the knees and the dorsum of hands and feet.

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The differential diagnosis of ainhum includes pseudoainhum, which includes a group of conditions such as congenital amnionic bands, bands secondary to specific diseases and traumatic bands. In the hair-thread tourniquet syndrome fibers of hair or thread become tightly wrapped around an appendage of an infant. The treatment is focused on immediately finding and removing the constricting fiber. Surgical exploration is necessary if complete removal cannot be verified. Most cases involving the toes are caused by hair, whereas most cases involving the fingers are caused by thread from mittens. A few cases of labial or penile strangulation were noted, providing yet another reason for physicians to routinely check the diapers of their pediatric patients.