What is Polydactyly?
Polydactyly is a term derived from two words: ‘poly’ meaning many and ‘dactylos’ meaning digits. It’s also referred to as hyperdactyly and is quite common among inborn abnormalities impacting hands and feet. This condition is described by having an additional finger or toe, which can occur due to irregular development of the limb during the early stages of pregnancy. Individuals can have polydactyly on its own (non-syndromic polydactyly) or it can be part of a syndrome, appearing alongside other birth defects (syndromic polydactyly).
Because polydactyly can be accompanied by other syndromic conditions, healthcare providers should be ready to assess a newborn baby with this condition for other associated disorders. They should also take note that polydactyly is more likely to appear on the right hand than the left, on the upper limb than the lower, and on the left foot rather than the right.
What Causes Polydactyly?
Polydactyly, which is having more than the usual number of fingers or toes, can sometimes happen on its own or it may be part of other syndromes. Some people with polydactyly might have relatives with the same trait. It can be linked to other conditions or syndromes such as Diamond-Blackfan anemia, an illness that causes a decrease in red blood cells; Fanconi anemia, a rare genetic disorder; Ellis-van Creveld syndrome characterized by dwarfism and heart defects; VACTERL, a disorder that affects multiple parts of the body; trisomy 13 and trisomy 21, both types of genetic disorders.
Scientists using advanced methods to study genes have found several different genes that are responsible for the development of polydactyly. These include GLI3, which is linked to Greig cephalopolysyndactyly syndrome, a disorder that affects the development of the limbs and the head. Other genes involved are SHH, FGF, ALX4, 5′-HoxD, ZNF141, MIPOL1, IQCE, and PITX1. Understanding these genes can help medicine understand why polydactyly happens and how to treat it.
Risk Factors and Frequency for Polydactyly
Polydactyly, or having more than the normal number of fingers or toes, is more common in Black individuals than in White individuals according to a study in the USA. It’s 10 times more common in Black males than White males and 22 times more common in Black females than White females. Specifically, the rates are as follows:
- For every 1,000 White males, around 2.3 have polydactyly.
- For every 1,000 Black males, around 13.5 have polydactyly.
- For every 1,000 White females, around 0.6 have polydactyly.
- For every 1,000 Black females, around 11.1 have polydactyly.
The occurrence of polydactyly around the world seems to be affected by genetics and race. When it comes to preaxial polydactyly, where the extra digits are on the thumb side of the hand or the big toe side of the foot, it occurs in 0.08 to 1.4 out of every 1,000 live births. This type is more common in Whites and also occurs quite frequently in Native American and Asian individuals.
On the other hand, postaxial polydactyly, where the extra digits are on the pinky side of the hand or the little toe side of the foot, is 10 times more common in the Black population compared to Whites. This type is more frequent than preaxial polydactyly and is often linked with other birth defects. It occurs in 1 to 2 out of every 1,000 live births.
Signs and Symptoms of Polydactyly
Polydactyly is a condition where a person is born with extra fingers or toes. This can be detected in infancy or sometimes, later in life. It can occur on its own or in combination with other birth defects. The condition can be classified into three main types based on which part of the hand or foot is affected: radial (thumbs side), ulnar (little finger side), and central (middle fingers or toes). In 1995, medical professionals decided to rename the types from preaxial and postaxial to radial and ulnar for better clarity.
The most usual case of polydactyly in the hand is radial polydactyly, which is seen more commonly in white individuals. Here, the extra fingers are usually located beside the thumb. For managing such patients, doctors usually refer to a classification by Wassel, made in 1969, which splits radial polydactyly into seven subtypes from type I to type VII. Ulnar polydactyly, which affects the little fingers, has a slightly different classification system, and is divided into type A and type B. These terms are used only for the upper limb.
In the case of the lower limb, the extra toes are classified differently. If the extra toe is next to the big toe, it’s called tibial polydactyly. If it’s next to the little toe, it’s called fibular polydactyly. When the three middle toes are affected, it is known as central polydactyly. The classification system for lower limb polydactyly was developed by Swanson and is based on the location of the extra toe.
Testing for Polydactyly
At around nine weeks into pregnancy, an ultrasound can show if a fetus develops extra fingers or toes, a condition known as polydactyly. If polydactyly is spotted, the doctor will need to check for other possible issues. A detailed ultrasound scan is required to examine the baby’s heart, kidneys, nervous system, and limbs to rule out associated medical conditions such as trisomy 13, Meckel-Gruber syndrome, Diamond-Blackfan anemia, and Fanconi anemia. To confirm if the polydactyly is an isolated case, meaning it’s not associated with any other condition, an additional ultrasound scan should be conducted between weeks 17 and 34 of the pregnancy.
After the baby’s birth, if polydactyly is confirmed, further tests should be carried out to check the structure of the extra digit. These tests will help doctors understand the precise structure of the extra digits and decide on the best type of surgery if necessary. Taking anteroposterior (front to back) and lateral (side) view X-rays should provide the required information for treatment options.
Treatment Options for Polydactyly
Treatment for polydactyly, a condition where a person is born with more than the usual number of fingers or toes, largely depends on the specifics of each case. For instance, the location of the extra digit and the intricacy of the condition will determine the type of treatment. The procedure could be as simple as an outpatient surgery, or it may require a more intricate approach involving the bones, ligaments, and tendons.
In some minor cases, the treatment can simply involve tying off the base of the extra digit. This interrupts the blood flow and gradually causes it to fall off.
In the early days after a baby is born, type A ulnar or postaxial polydactyly, which refers to an extra little finger, can be corrected by tying off the extra digit or removing it completely in an office visit using local anesthesia. There is, however, an increased risk of a painful condition known as neuroma (a growth or a tumor of nerve tissue) after tying off. To avoid this, the extra digit can be cleanly cut off. If the extra little finger is underdeveloped (type B), it can also be corrected by tying off until it naturally falls off after around 10-20 days.
If the extra digit is a thumb (known as preaxial or radial polydactyly) and affects the functioning of the hand, reconstructive techniques are used to ensure a stable, functional thumb. In this case, it’s generally recommended to consult with a surgeon specialized in hand surgery.
As for polydactyly in the foot, the treatment performed is aimed to improve appearance and quality of life. To minimize the effect on a child’s development and walking, surgery is generally performed when the child is approximately 1 year old. The treatment for this condition seems straightforward, but it does require careful decision-making before and during the surgical correction due to variations in deformities. In general, the treatment should be customized for each individual case.
In many cases, extra medial and lateral digits (toe(s) on the inner and outer sides of the foot) in both tibial and fibular polydactyly (extra toe(s) on the big toe side and small toe side) are usually removed via surgery. It’s important to avoid excessive angulation of the big toe (hallux varus) in tibial polydactyly treatments. Central polydactyly of the foot, an extremely rare occurrence where the extra digit forms in the middle of the foot, does not have a well-documented treatment approach. However, in most cases, the extra digits of this kind can be removed with a specific type of incision known as a racquet-shaped incision.
What else can Polydactyly be?
Polydactyly, a condition where a person or animal has more than the usual number of fingers or toes, may be found on its own or it may be a part of various syndromes. Some of these syndromes are:
- Trisomy 13
- Meckel syndrome
- Down syndrome
- Acrocallosal syndrome
- Basal cell nevus syndrome
- Diamond-Blackfan anemia
- Bardet-Biedl syndrome
- Biemond syndrome
- Fanconi anemia
- Ellis van Creveld syndrome
- McKusick-Kaufman syndrome
- Mirror hand deformity (ulnar dimelia)
- Mohr syndrome
- Oral-facial-digital syndrome
- Pallister-Hall syndrome
- Rubinstein-Taybi syndrome
- Short rib polydactyly
- VACTERL association (characterized by vertebral defects, anal atresia, cardiac defects, trachea-esophageal fistula, renal anomalies, and limb abnormalities)
What to expect with Polydactyly
The outlook is generally very good for children with polydactyly, which is a condition where a person is born with more than the usual number of fingers or toes. After undergoing surgery, most kids are able to have complete movement and use of their fingers and toes. However, if the child’s polydactyly is part of a syndrome that includes other birth defects, the outlook might be less promising. This is not because of the polydactyly itself, but due to the presence of other abnormalities.
Possible Complications When Diagnosed with Polydactyly
When a child’s hand has extra fingers, often referred to as polydactyly, there can be some complications. This can include bleeding and adverse reactions to anesthesia during the procedure to correct it. After the operation, the child might struggle with the hand’s functionality due to tense or loose ligaments. Another potential issue is the formation of a painful neuroma, especially when suture ligation is used for treatment. This complication occurs because the nerves in the extra finger are severed at skin level, preventing their natural retraction into the soft tissues. Therefore, these children have a higher chance of skin tag injuries, which can lead to skin breakdown.
Similarly, with polydactyly of the foot, where a child has extra toes, complications can also occur. The most common one with tibial polydactyly (extra toe next to the big toe) is hallux varus, a condition that causes the big toe to incline away from the other toes, which may require further surgery. For fibular polydactyly (extra toe next to the small toe), there might be some remaining angular deformity.
Here are the notable complications:
- Bleeding during procedure
- Adverse reaction to anesthesia
- Reduced hand functionality due to tense or loose ligaments
- Painful neuroma at the treatment site
- Skin tag injuries leading to skin breakdown
- Hallux varus for tibial polydactyly – condition that causes the big toe to incline away from other toes
- Angular deformity for fibular polydactyly
Recovery from Polydactyly
During the recovery period after surgery, doctors should keep a close eye on patients to check for any leftover or potential irregularities in body structure.
Preventing Polydactyly
Polydactyly, a condition where a person has more than the usual number of digits on their hands or feet, can be passed down from parents to their children. This condition usually follows what’s known as an ‘autosomal dominant pattern’ of inheritance. That means if a parent has this trait, their children, whether boys or girls, also have a chance of having the same condition.
Parents who have this trait or those who are concerned about it should be aware of ultrasound scans during pregnancy. These scans can help detect if a baby in the womb has polydactyly. Additionally, these scans are beneficial for screening for any other abnormal conditions that the baby might have.
