Background
Ainhum is the autoamputation of a digit, usually of the fifth toe bilaterally and as a result of a constricting scar in the form of a band or groove. Pseudoainhum is a similar condition that occurs as a secondary event resulting from certain hereditary and nonhereditary diseases that lead to annular constriction of digits.
Ainhum predominantly affects black patients in tropical regions. Although it has been reported in temperate areas, ainhum appears to be increasingly less common in the United States.[1, 2]
The origin of the term ainhum is unclear. In 1867, the term was used by da Silva Lima[3] from Bahia, Brazil to report the first published case. The word ainhum means fissure in the language of the Nagos tribe of Brazil and may be related to ayun, the word for saw in the Lagos tribe of Nigeria. The synonym for ainhum is dactylolysis spontanea.
Pathophysiology
In true ainhum, dactylolysis of a toe (most commonly, but not always,[4] the fifth toe) most likely is triggered by trauma; however, the true cause remains unknown. The trauma may be related to walking barefoot in the tropics. A fibrotic band develops from a flexural groove and progressively constricts the full radius of the toe until spontaneous autoamputation occurs. A similar progression occurs in pseudoainhum because of a collagen band, rather than from fibrosis. Pseudoainhum may be acquired or congenital. Additionally, ainhum occasionally affects fingers.
Ainhum of the finger. Courtesy of Hon Pak, MD, and reviewed by Ross Levy, MD. Epidemiology
Frequency
United States
Approximately 130 cases have been reported in the United States, but only 30 cases have been reported since 1960. Pseudoainhum is a rare disorder.
International
Ainhum is a relatively common disease among black Africans. In Africa, the incidence range is 0.2-2%. The incidence of true ainhum outside of Africa appears to be low.
Mortality/Morbidity
Pain may be severe in ainhum and in pseudoainhum. Because ainhum occurs primarily in tropical areas, secondary infections and their complications may be a source of morbidity.
Race
Ainhum has been reported to affect all races but occurs predominately in blacks. No racial predilection exists for pseudoainhum.
Sex
In Nigeria, one study revealed an incidence of 2.48 cases per 1000 males and 1.08 cases per 1000 females; however, recent investigations suggest no sex preference.
Age
Full-blown ainhum is uncommon in persons younger than 30 years and older than 50 years. The reason ainhum appears to be age specific is unclear. Early lesions may be observed in childhood.
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