POLYDACTYLY

Polydactyly is a condition in which one or more extra digits are present. The little finger is duplicated most often, followed by the thumb. The extra digit may vary from a simple skin tag to a completely developed finger.

Duplication of the small finger, in contrast to that of the thumb, is usually the result of an autosomal recessive trait and is often part of a syndrome. The radial aspect of the hand is involved a little more than the ulnar, and both are more common than central polydactyly (almost always associated with syndactyly and often shows disorganization of the skeleton).

CLASSIFICATION

There are several types of polydactyly, of varying frequency:

• Polydactyly alopecia seborrheic dermatitis
• Polydactyly cleft lip palate psychomotor retardation
• Polydactyly myopia syndrome
• Polydactyly postaxial dental and vertebral
• Polydactyly postaxial with median cleft of upper lip
• Polydactyly postaxial
• Polydactyly preaxial type 1
• Polydactyly syndrome middle ray duplication
• Polydactyly visceral anomalies cleft lip palate

 POSTAXIAL POLYDACTYLY (polydactyly on the ulnar side of the hand and fibula side of the foot).

1. Chondroectodermal dysplasia.
2. Short rib-polydactyly syndrome (types I and II).
3. Asphyxiating thoracic dystrophy.
4. Otopalatodigital syndrome.
5. Mesomelic dysplasia (Werner type).
6. Trisomy 13.
7. Meckel-Gruber syndrome.
8. Greig cephalopolysyndactyly syndrome.

Video clip of postaxial polydactyly

PREAXIAL POLYDACTYLY (polydactyly on the radial side of the hand and tibial side of the foot).

1. Chondroectodermal dysplasia.
2. Short rib-polydactyly syndrome type II.
3. Carpenter syndrome.
4. Greig cephalopolysyndactyly syndrome.

RADIAL DUPLICATION (THUMB)

• Type I - Bifid distal phalanx 2%
• Type II - distal phalanx duplicated 15%
• Type III - Bifid proximal phalanx 6%
• Type IV - proximal phalanx duplicated 43%
• Type V - Bifid metacarpal 10%
• Type VI - metacarpal duplicated 4%
• Type VII - Triphalangeal thumb (in one or both of the thumbs at any level) 20%

REFERENCES

1. Wladimiroff JW, Stewart PA, Reuss A et.al. Cardiac and extracardiac anomalies as indicators for trisomies 13 and 18: A prenatal ultrasound study. Prenat Diagn 1989;9:515.
2. Gershoni-Baruch R, Nachlieli T, Leibo R et.al. Cystic kidney dysplasia and polydactyly in 3 sibs with Bordet-Biedl syndrome Am J Med Genet 1992;44:269.
3. Benacerraf BR, Miller WA, Frigoletto FD Jr. Sonographic detection of fetuses with trisomy 13 and 18: Accuracy and limitations. Am J Obstet Gynecol 1988;158:404.