Polydactyly affects about 1 in 1,000 individuals around the world. It is a condition where one or more extra fingers or toes are present at birth. Its name is derived from the Greek words for ‘many’ (poly) and ‘digits’ (dactylos).

Symptoms

There are three different ways in which polydactyly may manifest:

• Postaxial polydactyly or small finger duplication, referred to as ulnar polydactyly if it affects the fingers, and fibular polydactyly if it affects the toes. In this condition, the extra finger or toe is present on the outer side of the little finger or little toe. This is the most common form of polydactyly. It may occur on just one hand or foot, but can often occur in symmetry.

• Preaxial polydactyly or thumb duplication, referred to as radial polydactyly if it affects the fingers, and tibial polydactyly if it affects the toes. In this condition, the extra finger or toe is present on the outer side of the thumb or big toe. This form of polydactyly is less common and usually occurs in isolation (i.e. with no other associated syndrome). It often occurs on only hand or foot.

• Central polydactyly, where the extra finger is attached to one of the middle three fingers or toes. This is a rare condition, and is sometimes associated with the incidence of webbed hands or feet.

Complications

There are usually no complications that arise from the incidence of polydactyly by itself. However, if the condition is a consequence of some other disorder, treatment and care may be a little more complicated than otherwise.

Causes

Most cases of polydactyly occur in isolation, i.e. with no other associated syndrome, and are therefore referred to as isolated or nonsyndromatic polydactyly. This has often been found to be associated with the inheritance of specific genes – six of which have been identified through research, and is therefore categorised as ‘familial’. As such, small finger duplication is usually hereditary, with African Americans have ten times more risk of developing the condition.

There are also ‘nonfamilial’ cases that may be linked to environmental factors such as maternal diabetes, low birth weight, maternal epilepsy, exposure to certain drugs or diseases as an embryo.

Syndromatic polydactyly refers to polydactyly associated with other syndromes that are usually caused by genetic mutations which affect embryonic development. Small finger duplication is believed to be more common as a syndromatic condition among Caucasians.

Diagnosis

In some cases, the presence of extra fingers or toes may be observed in ultrasound scans carried out during pregnancy. If not, polydactyly will be apparent and noticed upon the birth of the child. X-ray imaging enables a clearer diagnosis and analysis of each case – allowing doctors to see whether an extra digit has bone and other internal observations.

Prevention

Apart from the general care (physical and medical) to be taken during pregnancy, there is no specific means by which polydactyly may be prevented.

Treatment

The treatment administered for polydactyly depends on the type and nature of manifestation, and is usually carried out while the individual is still a child. Optimal age and method should be discussed with the doctor/surgeon.

• In the case of small finger duplication, if the extra finger is not fully developed and has no bone (called a ‘nubbin’), it may be tied at the base and allowed to fall off naturally. However, this often leaves behind a bump, hence surgery is preferred nowadays. If the finger is fully developed, surgery is the only way to go about removal of the extra digit. In the majority of cases, treatment is done more for cosmetic reasons as functionality is rarely affected.

• In the case of thumb duplication, treatment may be more complex as the extra thumb or big toe may impact the function of the normal digit due to its angle and shape being altered. Hence, reconstructive surgery may be required for the functioning digit – sometimes using parts of both digits.

• In the case of central polydactyly, it may not always be possible to remove the extra finger. In the event where surgery is carried out, reconstructive surgery usually follows removal of only the extra finger, or removal of two fingers and re-modelling of a new finger. Follow-up surgeries may be required, and in some cases a cast or pin (inserted) may be required to fasten the bones while they heal. In some instances, surgery may only be carried out on the tendons and ligaments attached to these fingers in order to prevent deformity.

Treatment of isolated nonsyndromatic polydactyly is more straightforward than syndromatic polydactyly, where the effect and relationship to related syndromes should also be factored in.

Cover illustration from twinkl.com.qa.