Ainhum (dactylolysis spontanea) is a condition of idiopathic etiology involving a bandlike constriction of the soft tissue of a digit. Generally, the constriction presents bilaterally, with involvement of the fifth digit most commonly. 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.
The origin of the term ainhum is unclear. In 1867, the term was used by da Silva Lima
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.