Ainhum, or dactylolysis spontanea, is characterized by the development of a progressive deepening and constricting band (sulcus) that encircles a digit resulting in spontaneous amputation. The disease occurs most commonly in dark-skinned individuals in Africa, Asia, South and Central America, and the United States. Although very rare in the United States, some authors suggest that it is underdiagnosed and overlooked.

Ainhum occurs in 4 progressive stages, which may take years to fully develop. It begins with the formation of the sulcus, next edema results from the deepening of the sulcus, followed by autoamputation, and then, in the final stage, necrosis completes the amputation. The cause of ainhum is unknown, although many etiologies have been suggested, including impaired blood supply to the little toe.

Ainhum should be distinguished from pseudoainhum, which is congenital or associated with other acquired diseases, including psoriasis, disorders of keratinization, connective tissue diseases, and trauma, among others.