Ainhum, also known as dactylolysis spontanea,is a poorly understood condition in which the fifth toe (the little one) becomes constricted at its base and eventually falls off.
This condition was first described over 100 years ago by the English surgeon Robert Clarke, who called “dry gangrene,” and we are not much closer to understanding it today than we were then.
Even the origin of the condition’s name is unclear—ainhum is either of African or Portuguese origin, possibly derived from the African Yoruba word ayùn, meaning “to saw (off).”
What Causes of Ainhum?
The exact cause of toes falling off is still unknown. It is almost never linked to injury of any kind, and the most intuitively likely causes—bacteria, viruses, parasites, and fungi—have all been ruled out.
Some evidence exists linking ainhum to walking barefoot in childhood, but many cases have been observed in which the victim never went barefoot.
In many cases —but by no means in all—corns or warts have been observed to appear on the end of the doomed toe shortly before the first lesion is noticed, but what relevance this has (if any) has yet to be determined.
Ainhum almost exclusively strikes people of African descent, especially people who live in West Africa, India, and South America.
The evident role of race as a predisposing factor in this condition suggests that it may be genetic in origin, and there have been reports of ainhum running in families.
Men appear to be more susceptible than women; the ratio of male victims to female is two to one. Victims tend to be in their thirties and forties, although at least one case has been reported involving a seven-year-old child.
Ainhum is very rare—few cases have ever been reported in the United States (mostly in the South, and almost never in the Northeast), and even fewer in Europe, although the condition is much more common in Nigeria, where it strikes nearly two people out of every thousand.
Symptoms and Progression of Ainhum
Ainhum generally begins with the appearance of a small groove in the plantar-digital fold, at the base of the little toe, on the bottom (it almost never happens to any other toe).
Over a period of months—and sometimes years—this groove becomes deeper and longer, eventually encircling the entire toe.
The rate at which the condition spreads varies greatly from one case to the next; in some cases the band around the toe is a complete circle within a few months, and in other cases the process takes years.
Both feet are affected in about 75 percent of cases, although the condition is usually more severe and more pronounced in one foot than in the other.
The condition is painful in about 78 percent of cases due to pressure on the nerves lying beneath the band of constriction.
As the condition worsens, fracture of the phalanx may occur, or sepsis may set in, either of which causes severe pain. However, a toe falling off is less painful than one might expect, and in some cases there is no pain.
Eventually the end of the toe swells up until it resembles a potato. This swelling is due to the accumulation of lymphatic fluid in the distal part of the toe (the part that is on the far side of the constriction band).
When the condition has reached this stage, crusts may begin to form in the groove, and there is a risk of Staphylococcus infection.
As the groove becomes deeper, blood vessels, tendons, and nerves become compressed, worsening the pain.
The pressure causes bone to be absorbed into the toe, and eventually everything in front of (or distal to) the point of constriction is compressed into a cord of tissue with no blood vessels running through it.
The connection between the foot and what is left of the toe becomes slim and tenuous, and if the toe is not amputated it will eventually fall off on its own. Surprisingly, there is no bleeding when this occurs.
While the progress of dactylolysis spontanea varies, it generally takes five years from the first appearance of the groove for the toe to drop off completely.
How is Ainhum Diagnosed?
Due to its rarity, ainhum is easily misdiagnosed, and it is sometimes confused with leprosy, diabetic gangrene, and other conditions.
How is Ainhum Treated?
Unfortunately, because the phenomenon of toes falling off is so poorly understood, there is no way to prevent it and not much that can be done to treat it. If the condition is caught in its early stages, the groove can be excised and the scar treated with a plastic surgery procedure known as Z-plasty.
This action will relieve the pain and can sometimes stop the progress of ainhum, thereby saving the toe. Advanced cases can sometimes be treated by disarticulating the metatarsophalangeal joint (separating the phalanx bone at the base of the toe from the foot’s metatarsal bone), which relieves pain and maintains the stability and usefulness of the foot.
These treatments are not always possible, however, and in most cases surgical amputation of the toe is the only recourse.