Ainhum is a painful constriction of the base of the fifth toe
frequently followed by bilateral spontaneous amputation (autoamputation
) a few years later. The disease occurs predominantly in black Africans and their descendants. The exact etiology is still unclear.
Ainhum was first reported as a distinct disease and described in detail by J. F. da Silva Lima in 1867. He recognised a disease of the fifth toe suffered by the Nagos tribe of Bahia, Brazil. This disease was called “ainhum” by the Nagos and means “to saw”, characterising the painful loss of the fifth toe. The origin of these term was thought to be African. Due to slave trade, the Nagos were related to a native tribe in Nigeria.
Ainhum predominantly affects black people, living in West Africa, South America and India. In Nigeria
it is a common disease with an incidence of 2.2%. Daccarett recorded retrospectively a rate of 1.7% in a mainly African American population in Chicago. Up to now only a few cases had been reported in Europe. Ainhum usually affects people between 20 and 50 years. The average age is about thirty-eight. The youngest recorded patient was seven years old. There is no predominant gender ratio.
Etiology and Pathogenesis
The true cause of ainhum remains unclear. It is not due to infection by parasites
, and it is not related to injury. Walking barefoot in childhood had been linked to this disease, but ainhum also occurs in patients who have never gone barefoot. Race seems to be one of the most predisposing factors and it may has a genetic component, since it has been reported to occur within families. Dent et al. discussed a genetically caused abnormality of the blood supply to the foot. Peripheral limb angiography in five limbs with ainhum showed that the posterior tibial artery became attenuated at the ankle, and the plantar arch and its branches were absent. The dorsal pedis artery was constituting the only supply to the forefoot and little toe.
The groove begins on the lower and internal side of the base of the fifth toe, usually according to the plantar-digital fold. The groove becomes gradually deeper and more circular. The rate of spread is variable, and the disease may progress to a full circle in a few months, or still be incomplete after years. In about 75 per cent both feet are affected, though not usually to the same degree. There is no case reported where it begins in any other toe than the fifth, while there is occasionally a groove on the fourth or third toe. The distal part of the toe swells and appears like a small “potato”. The swelling is due to lymphatic edema distal to the constriction. After a time crusts can appear in the groove which can be infected with staphylococcus
While the groove becomes deeper, compression of tendons, vessels and nerves occurs. Bone is absorbed by pressure, without any evidence of infection. After a certain time all structures distal the stricture are reduced to an avascular cord. The toe’s connection to the foot becomes increasingly slender, and if it is not amputated, it spontaneously drops off without any bleeding. Normally it takes about five years for an autoamputation to occur. Cole describes four stages of ainhum:
• Grade I: groove
• Grade II: floor of the groove is ulcerated
• Grade III: bone involvement
• Grade IV: autoamputation has occurred
Pain is present in about 78% of cases. Slight pain is present in the earliest stage of ainhum, caused by pressure on the underlying nerves. Fracture of the phalanx or chronic sepsis is accompanied with severe pain.
Histology shows a change in the prickle cell layer, and this is responsible for the laying down of condensed keratin causing the groove. The junctional tissue is reduced to a slender fibrous thread, almost avascular, and all the tissues beyond the constricting band is repressed by a fibro-fatty mass covered by hyperkeratotic integument.
Soft tissue constriction on the medial aspect of the fifth toe is the most frequently presented radiological sign in the early stages. Distal swelling of the toe is considered to be a feature of the disease. In grade III lesions osteolysis
is seen in the region of the proximal interphalangeal joint with a characteristic tapering effect. Dispersal of the head of the proximal phalanx is frequently seen. Finally, after autoamputation, the base of the proximal phalanx remains. Radiological examination allows early diagnosis and staging of ainhum. Early diagnosis is crucial to prevent amputation.
Ainhum is an acquired and progressive condition, and thus differs from congenital annular constrictions. Ainhum has been much confused with other diseases such as leprosy
, diabetic gangrene
or Vohwinkel syndrome
Incisions across the groove turned out to be ineffective. Excision of the groove followed by z-plasty could relieve pain and prevent autoamputation in Grade I and Grade II lesions. Grade III lesions are treated with disarticulating the metatarsophalangeal joint. This also relieves pain, and all patients have a useful and stable foot.