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At a glance

A narrow strip of hardened skin with constricting ring formation on the little toe at the level of digitoplantar fold, progressively leading to spontaneous amputation.

Synonym

Dactylolysis Spontanea. The origin of the word Ainhum is not entirely clear, but is usually thought to be derived from the Nago/Yoruba language in Nigeria, meaning “to saw” or “to cut.”

Genetic inheritance

Familial occurrence with autosomal dominant inheritance has been described, but many sporadic cases have been reported. Both sexes are affected and can occur at basically any age (even in children).

Clinical aspects

Ainhum is characterized by the occurrence of a circular constriction band most often located at the root of the fifth toe or rarely of a finger in an otherwise healthy patient. As constriction progresses, the distal phalanx of the toe exhibits bulbous and most often painful swelling (lymphedema) and the toe becomes disabled, and finally, after few months or several years, results in spontaneous amputation (autoamputation). The amputation may be the result of a minimal trauma and typically involves only minor pain or bleeding. The process is often bilateral and occasionally the fourth or third toe may become involved later on. The disorder typically appears in people with dark-skin color. Classic features of the affected digit include hyperkeratosis, chronic dermatitis, ligamentous destruction, and finally osteoporosis with cortical bone resorption. Histopathological examination reveals severe hyperkeratosis, acanthosis, parakeratosis, fibrosis, and chronic subcutaneous inflammatory changes. While the nerves are usually spared until late in the disease process, the localized fibrosis results in scarring of muscular tissue, sweat glands, and blood vessels. Although the origin of the disease remains to be elucidated, mechanical and/or inflammatory causes have been favored by many authors. Bacterial superinfection with ulceration is not uncommon.

There are four grades of the disease:

  • Grade I: The affected digit presents with a groove on the distal part of the toe, but signs of swelling or osseous involvement are absent.

  • Grade II: The digit becomes externally rotated and the part distal to the constriction band shows bulbous swelling.

  • Grade III: There is radiological evidence for osseous involvement.

  • Grade IV: Autoamputation.

A second classification distinguishes four stages:

  • Stage I: A crease appears at the digitoplantar fold and deepens into a sulcus

  • Stage II: The sulcus extends around the base resulting in bulbous swelling of the toe

  • Stage III: Voluntary motion is lost in the constricted toe

  • Stage IV: Autoamputation occurs

Conservative therapy in the early stages may include topical salicylate preparations, retinoids, and topical or intralesional corticosteroids. Surgical options consist of Z-plasty for grade I and early grade II. However, once osseous changes are present, the prognosis with regards to saving the toe becomes poor and elective surgical amputation is offered to reduce discomfort.

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