Polydactyly

Polydactyly (ie “supernumerary digit”) is a condition in which an individual has greater than 5 fingers or toes on a hand or foot, with extra fingers being more common than extra toes. The original classification was created in 1978 and is broken down into categories depending on the location of the extra digit: preaxial (thumb or great toe), central (2nd/3rd/4th duplication) or postaxial (pinky/5th finger or toe) side.1 The extra finger or toe can occur in isolation or can be associated with other birth defects or syndromes about 15% of the time.2

Polydactyly is 10 times more frequent in black versus white males and 22 times more frequent in black females than white females, according to one study comparing the Southern USA and Sweden.3 All children must be assessed for other associated abnormalities. Since it is a condition that is generally uncommon in Caucasians, genetic workup should be considered in a Caucasian child with polydactyly.

Preaxial Polydactyly: Preaxial polydactyly means that the extra digit(s) is on the thumb or big toe side. Isolated preaxial polydactyly in the hand is more common in Caucasians compared to African Americans, and has a high incidence in the Native American and Asian populations.4-6 In pre-axial polydactyly of the hand, preserving hand and thumb function in terms of pinch grip, grasp and release are important. Surgical management depends on the how much and what of the digit (thumb/toe) is duplicated and what muscles and tissues are attached.4 The general principle is to remove the least functional components and reconstruct the remaining parts.4 This should be done by a hand specialist. In the foot, the most common reasons for surgery are difficulty with shoe wear and cosmesis or how it looks.7

Postaxial Polydactyly: Postaxial polydactyly means that extra digits are attached to the 5th digit side of the hand or foot, ranging from a skin tag to a fully duplicated finger or toe. In the hand, this is 10 times more common in the African & African American population compared to Caucasians.4 If there are no other apparent birth defects or syndrome, it is considered an autosomal dominant genetic change with variable penetrance.4 This means that when it is present, that person has a up to a 50% chance of having a child with the same thing and also that one of the parents likely had an extra digit as well. In black children, it is usually an isolated finding. When present in Caucasians, it is often associated with a syndrome and requires further work-up.4 If the extra digit only involves skin and soft tissue with no bone, it is often treated at birth by the pediatrician or obstetrician by tying a suture around it and allowing it to auto-amputate or fall off just with this small intervention.4 If bone is also involved, a specialized surgeon should perform the removal and reconstruction.

When polydactyly is the only finding and there are no other signs of major organ (heart, kidney, genital etc) or facial abnormalities, it is typically an isolated finding and not related to syndromes. However, since there are many syndromes that are associated with polydactyly, it is important to review the child’s medical history and to look for abnormal facial features or other signs of organ dysfunction that may indicate a global syndrome. When presenting as an isolated condition, polydactyly can be a correctable issue with a good outcome.

Summary

Preaxial polydactyly: Thumb or great toe side extra digit. Can be seen more frequently in Caucasian, Native American and Asian populations; can present as an isolated issue or can be related to a syndrome.

Postaxial polydactyly: 5 th finger or toe side extra digit. Is seen more frequently in African and African American populations and is less commonly associated with a syndrome.

finger or toe side extra digit. Is seen more frequently in African and African American populations and is less commonly associated with a syndrome. Children with polydactyly should be examined for other abnormalities or signs of syndromes; however, many children have isolated polydactyly and good long term outcomes.

References

Temtamy SA, McKusick VA. The genetics of hand malformations. Birth Defects Orig Artic Ser. 1978;14(3):364-439. Castilla EE, Lugarinho R, da Graça Dutra M, Salgado LJ. Associated anomalies in individuals with polydactyly. American Journal of Medical Genetics Part A. 1998;80(5):459-465. Finley WH, Gustavson KH, Hall TM, Hurst DC, Barganier CM, Wiedmeyer JA. Birth defects surveillance: Jefferson county, Alabama, and Uppsala county, Sweden. South Med J. 1994;87(4):440. Guo B, Lee SK, Paksima N. Polydactyly: a review. Bull Hosp Jt Dis. 2013;71(1):17-23. Cohen MS. Thumb duplication. Hand Clin. 1998;14(1):17-27. Hosalkar H, Shah H, Gujar P, Kulkarni A. Crossed polydactyly. J Postgrad Med. 1999;45(3):90. Venkatnarsimha M, Linton JL, Barnes DA. The spectrum of pre-axial polydactyly of the foot. J Pediatr Orthop 2011;31:435–447.

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