Understanding Mirror Hand Syndrome : Causes, Symptoms, and Treatments

Mirror hand syndrome or ulnar dimelia, is an extremely rare congenital birth defect that affects the hands. Sometimes, the forearm and elbow might also be impacted. In most cases of mirror-hand syndrome, there is mirrored symmetry of the hand with a central digit and three digits on either side. So, when we see from the midpoint of the hand in the affected individuals, the fingers look like mirror images. Thus children with mirror hand syndrome are generally born with seven to ten fingers on one or both of their hands. Usually, there is no thumb in individuals with mirror hand syndrome. So, only the middle finger, ring, and little fingers can be seen on either side of the central finger.

Individuals with mirror hand syndrome, often have limited mobility in their fingers, forearms, and elbow. The condition affects women and men equally.

The exact cause of mirror hand syndrome or ulnar dimelia is still unknown, however, doctors believe genetics play a role in the appearance of this congenital birth defect. Generally, we have two bones in our forearms, namely the ulna and the radius. Both these bones lend to the growth of different hands and fingers. However, in the case of mirror-hand syndrome, there are two ulna bones, and the radius bone is lost.⁽¹⁾ This occurs in children or babies when the limb is still in the developing stages as an embryo.

Sometimes, the wrist bones also duplicate and this results in the forearm and hand looking like mirror images. According to experts, it has been mentioned that mirror hand syndrome could be of different types. Although, most of the time two ulnae without a radius bone occur, at times there could be two ulnae bones along with a radius bone. If these bones develop differently, the physical appearance of the hand also differs.

The physical appearance of more than five fingers, no thumb, and mirror images of the hand (or both hands) is the most common symptom of mirror hand syndrome. However, apart from this, some other symptoms associated with mirror hand syndrome include:

• The condition can cause the wrist to be slightly bent in many children.
• The affected children might be able to bend their elbows regularly. However, in certain cases, their elbow could be straight, and bending or rotating their elbows becomes almost impossible.
• This congenital birth defect can cause one to have a limited range of motion in the hand and wrist. Ultimately, this can cause dexterity issues, which means using the hand and fingers to perform specific day-to-day activities like picking things up or holding things could also become quite difficult.

Mostly, mirror hand syndrome is often diagnosed at the prenatal ultrasound screening during pregnancy and at times it can also be diagnosed at birth. Once the condition is diagnosed, doctors prescribe for surgical reconstructions of the affected hands. Usually, the reconstruction surgery should be performed before the age of two in children.^{(2, 3)}

Reconstruction surgery is done to fix the physical appearance and also improve the function of the affected hand. Multiple surgeries might be required to fix the physical appearance.

During the surgery, surgeons remove additional fingers and mostly fix one of the digits to be used as a thumb.  This digit which needs to act like a thumb, is repositioned at the place where the thumb is usually present in normal hands. This is known as pollicization and it aims at building hands with five fingers including a thumb.

Doctors try to keep more muscle, tendon, and growth plates on the hands and also reconstruct the wrists, which helps the affected children develop hand movement, growth, and function.

Physical therapy and motion exercises are essential for the hand to improve mobility and function as the children grow. A physical therapist or an occupational therapist would help you know more about the exercises.

Mirror hand syndrome, also known as Ulnera dimelia is a congenital birth defect, where there is a mirror symmetry of the affected hand. Children with mirror-hand syndrome usually find it hard to perform normal day-to-day tasks. However, with reconstruction surgery, the condition can be improved and one can perform normal tasks with ease. If your babies are suffering from such a congenital birth defect, consult with their doctor and try to treat the condition as early as possible.

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