Supernumerary Digit

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Background

Polydactyly is the most common congenital digital anomaly of the hand and foot. It may appear in isolation or in association with other birth defects. Isolated polydactyly is often autosomal dominant, while syndromic polydactyly is often autosomal recessive.[1]  See the image below.



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Supernumerary digit, no magnification.

Pathophysiology

Early theories for polydactyly concerned disorders in the programmed cell death cycle of fetal limb development. Current theories focus on mutations in specific genetic locations that cause limb development to go awry.[2]

Many specific mutations have been linked to polydactyly; however, a molecular etiology has not been found in a third of human disorders associated with polydactyly.[3]

Mammals have been shown to have genetic clusters identified as homeobox or Hox genes corresponding to five domains across the limb bud. According to Muragaki et al,[4] mutations in the HOXD13 gene are associated with synpolydactyly.

The steps in limb development and outgrowth are controlled by at least two described signal centers, as follows[3] :

  1. Zone of polarizing activity (ZPA) - Sonic Hedgehog is a molecule found to mediate ZPA activity
  2. Apical ectodermal ridge (AER) - Expresses fibroblast growth factors

As limb growth in utero progresses along a preset timeline, elongation of the limb, development of soft tissue, and differentiation of digits progresses.

The Medscape Genomic Medicine Research Center may be of interest.

Epidemiology

Frequency

United States

Despite being a common malformation, the true incidence of polydactyly is not fully known. The epidemiologic data on polydactyly is limited because most birth defect registries do not include the entity. One study by Finley et al[5] combined data from Jefferson County, Alabama and Uppsala County, Sweden. This study showed incidence of all types of polydactyly to be 2.3 per 1000 in white males, 0.6 per 1000 in white females, 13.5 per 1000 in black males, and 11.1 per 1000 in black females. The Swedish data alone showed polydactyly of all types to have an incidence of 1.0 per 1000, equally distributed between males and females.

International

Genetic and ethnic factors seem to influence the nature of polydactyly in the world population. Unfortunately, the knowledge of polydactyly is limited to select studies of certain subpopulations. Preaxial polydactyly is very common in various Asian populations, accounting for 90% of cases in South China, Hong Kong, and Japan. Duplicated thumbs at the metacarpophalangeal level are the usual anomaly.[6, 7]

Race

Postaxial hand polydactyly is a common isolated disorder in black children, and autosomal dominant transmission is suspected. In contrast, postaxial polydactyly seen in white children is usually syndromic and associated with an autosomal recessive transmission. Postaxial polydactyly is approximately 10 times more frequent in blacks than in whites and is more frequent in male children. 

Other factors associated with postaxial hand polydactyly include twinning, low maternal education, parental consanguinity, occurrence in first-degree relatives, and maternal bleeding in the first trimester.

History

Polydactyly is the most common congenital digital anomaly of the hand and foot. It may appear in isolation or in association with other birth defects.[8]

Physical Examination

Temtamy and McKusick[9] classified polydactyly into preaxial, central, and postaxial types. Preaxial polydactyly refers to the duplication of the first digit. Central polydactyly involves duplication of the second, third, or fourth digit. Postaxial polydactyly involves the fifth digit. The terms radial, central, and ulnar can be used to describe polydactyly in the upper extremity. Similarly, the terms tibial, central, and fibular can be used to describe polydactyly in the lower extremity.

The association of hand and foot polydactyly is uncommon. If hand and foot polydactyly does occur, it may be a case of "crossed polydactyly"—when preaxial involement of the hand and postaxial involvement of the foot occurs or vice versa.

Synpolydactyly is the combination of syndactyly and polydactyly.[10, 11]

Imaging Studies

Prenatal ultrasound

Fetal finger buds can be seen using transvaginal ultrasound as early as 9 weeks and reliably by 13 weeks of pregnancy. Once polydactyly is established, a thorough ultrasound evaluation, especially of the heart, nervous system, limbs, and kidneys, to identify an associated syndrome (eg, Meckel-Gruber syndrome, trisomy 13) should be performed. Follow-up ultrasound between 17 and 34 weeks with biometric profile is recommended to establish the diagnosis of isolated polydactyly.[14, 15]

Radiographs

Radiographs of the affected limb are recommended to show whether the rudimentary digit contains skeletal elements. The degree of deviation of the digit and the size of the articulating metacarpal or metatarsal also may be helpful in surgical planning.

Histologic Findings

Rudimentary polydactyly, which may be a type of congenital traumatic neuroma, shows hyperkeratosis and acanthosis overlying many nerve bundles in the dermis. It may appear as a papule on the base of the ulnar side of the little finger. Abundant Merkel cells may appear at first and then disappear after the development of these nerve bundles, which form Meissner corpuscles in the dermal papillae and stain positively with S-100 protein.[16]

See the histology slides below.



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Supernumerary digit, no magnification.



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Twenty-eight-day-old supernumerary digit, connective tissue and epidermis (40x).



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Twenty-eight-day-old supernumerary digit, nerve bundle base (40x).

 



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Twenty-eight-day-old supernumerary digit, rudimentary nail unit cartilage (2x).

Surgical Care

A child with distal extremity anomalies experiences emotional stress.[17] By age 3 years, the child has become aware of the anomaly. By age 7 years, the child has begun to experience the close scrutiny of his peers at school. For these reasons, along with others, surgical correction should be initiated early in life.

Surgical management depends greatly on the complexity and location of the deformity. Traditionally, postaxial polydactyly was managed by pediatricians with suture ligation and only syndactyly was treated in the operating room. However, the increased risk of painful neuromas when using suture ligation has led to the use of sharp excision for postaxial polydactyly. The accessory digital nerve in postaxial polydactyly needs to be identified and transected as far proximally as is safe in order to decrease the risk of neuroma. Soft tissue then covers the end of the divided nerve. In cases of preaxial and central polydactyly, treatment is variable and the surgeon looks to find a balance between aesthetics and functionality. Waiting until age 9-12 months is advisable to decrease anesthesia risk.[18, 19, 20, 21]

Conversely, if an infant has postaxial type B polydactyly (rudimentary extra digit attached to the ulnar side by a soft tissue stalk), excision in the neonatal nursery is a safe and simple procedure with consistently positive outcomes. Excision is done with a single swipe of a scalpel after the use of topical anesthesia.[22] .

When preaxial polydactyly involves the radial hand and thumb, reconstructive techniques are usually needed to ensure a functional and stable thumb.[23]  Consultation with a surgeon with special expertise in hand problems is typically warranted.

A related Medscape article is Polydactyly of the Foot.

Complications

Complications in the perioperative timeframe include those secondary to bleeding and anesthesia.

Later, decreased function due to ligamentous laxity or contracture can occur. Painful neuromas can also occur at the treatment site, especially when using suture ligation as therapy.[21]

Author

Luke Lennox, MD, Resident Physician, Department of Dermatology, Case Western Metro Health Medical Center

Disclosure: Nothing to disclose.

Coauthor(s)

Thomas N Helm, MD, Clinical Professor of Dermatology and Pathology, University of Buffalo, State University of New York School of Medicine and Biomedical Sciences; Director, Buffalo Medical Group Dermatopathology Laboratory

Disclosure: Nothing to disclose.

Specialty Editors

Richard P Vinson, MD, Assistant Clinical Professor, Department of Dermatology, Texas Tech University Health Sciences Center, Paul L Foster School of Medicine; Consulting Staff, Mountain View Dermatology, PA

Disclosure: Nothing to disclose.

Robert A Schwartz, MD, MPH, Professor and Head of Dermatology, Professor of Pathology, Professor of Pediatrics, Professor of Medicine, Rutgers New Jersey Medical School

Disclosure: Nothing to disclose.

Chief Editor

Dirk M Elston, MD, Professor and Chairman, Department of Dermatology and Dermatologic Surgery, Medical University of South Carolina College of Medicine

Disclosure: Nothing to disclose.

Additional Contributors

Albert C Yan, MD, Section Chief, Associate Professor, Department of Pediatrics, Section of Dermatology, Children's Hospital of Philadelphia and University of Pennsylvania School of Medicine

Disclosure: Nothing to disclose.

Carter G Abel, MD, Clinical Assistant Attending, Department of Dermatology, New York Presbyterian Hospital

Disclosure: Nothing to disclose.

Denise M McCarthy, MD, Associate Professor, Department of Radiology, Morristown Memorial Hospital

Disclosure: Nothing to disclose.

References

  1. Hosalkar HS, Shah H, Gujar P, Kulkarni AD. Crossed polydactyly. J Postgrad Med. 1999 Jul-Sep. 45(3):90-2. [View Abstract]
  2. Wattanarat O, Kantaputra PN. Preaxial polydactyly associated with a MSX1 mutation and report of two novel mutations. Am J Med Genet A. 2015 Oct 13. [View Abstract]
  3. Bouldin CM, Harfe BD. Aberrant FGF signaling, independent of ectopic hedgehog signaling, initiates preaxial polydactyly in Dorking chickens. Dev Biol. 2009 Oct 1. 334 (1):133-41. [View Abstract]
  4. Muragaki Y, Mundlos S, Upton J, Olsen BR. Altered growth and branching patterns in synpolydactyly caused by mutations in HOXD13. Science. 1996 Apr 26. 272(5261):548-51. [View Abstract]
  5. 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 Apr. 87(4):440-5. [View Abstract]
  6. Cohen MS. Thumb duplication. Hand Clin. 1998 Feb. 14(1):17-27. [View Abstract]
  7. Hung L, Cheng JC, Bundoc R, Leung P. Thumb duplication at the metacarpophalangeal joint. Management and a new classification. Clin Orthop Relat Res. 1996 Feb. 31-41. [View Abstract]
  8. Klaassen Z, Shoja MM, Tubbs RS, Loukas M. Supernumerary and absent limbs and digits of the lower limb: a review of the literature. Clin Anat. 2011 Jul. 24(5):570-5. [View Abstract]
  9. Temtamy SA, McKusick VA. The genetics of hand malformations. Birth Defects Orig Artic Ser. 1978. 14(3):i-xviii, 1-619. [View Abstract]
  10. Malik S, Grzeschik KH. Synpolydactyly: clinical and molecular advances. Clin Genet. 2008 Feb. 73(2):113-20. [View Abstract]
  11. Tian F, Tian LJ, Zhao W, Li XC, Li B, Ji XL. Plastic repair for a case with synpolydactyly. Arch Orthop Trauma Surg. 2011 Jun. 131(6):869-73. [View Abstract]
  12. Castilla EE, Lugarinho R, da Graça Dutra M, Salgado LJ. Associated anomalies in individuals with polydactyly. Am J Med Genet. 1998 Dec 28. 80(5):459-65. [View Abstract]
  13. Jafari D, Sharifi B. A variant of mirror hand. A case report. J Bone Joint Surg Br. 2005 Jan. 87(1):108-10. [View Abstract]
  14. Bromley B, Shipp TD, Benacerraf B. Isolated polydactyly: prenatal diagnosis and perinatal outcome. Prenat Diagn. 2000 Nov. 20(11):905-8. [View Abstract]
  15. Zimmer EZ, Bronshtein M. Fetal polydactyly diagnosis during early pregnancy: clinical applications. Am J Obstet Gynecol. 2000 Sep. 183(3):755-8. [View Abstract]
  16. Ban M, Kitajima Y. The number and distribution of Merkel cells in rudimentary polydactyly. Dermatology. 2001. 202(1):31-4. [View Abstract]
  17. Eskandari MM, Oztuna V, Demirkan F. Late psychosocial effects of congenital hand anomaly. Hand Surg. 2004 Dec. 9(2):257-9. [View Abstract]
  18. Morley SE, Smith PJ. Polydactyly of the feet in children: suggestions for surgical management. Br J Plast Surg. 2001 Jan. 54(1):34-8. [View Abstract]
  19. Park GH, Jung ST, Chung JY, Park HW, Lee DH. Toe component excision in postaxial polydactyly of the foot. Foot Ankle Int. 2013 Apr. 34(4):563-7. [View Abstract]
  20. Dijkman R, Selles R, van Rosmalen J, Hülsemann W, Mann M, Habenicht R, et al. A clinically weighted approach to outcome assessment in radial polydactyly. J Hand Surg Eur Vol. 2015 Aug 28. [View Abstract]
  21. Hartzell TL, Taylor H. Traumatic amputation of a supernumerary digit: a 16-year-old boy's perspective of suture ligation. Pediatr Dermatol. 2009 Jan-Feb. 26 (1):100-2. [View Abstract]
  22. Katz K, Linder N. Postaxial type B polydactyly treated by excision in the neonatal nursery. J Pediatr Orthop. 2011 Jun. 31 (4):448-9. [View Abstract]
  23. Comer GC, Potter M, Ladd AL. Polydactyly of the Hand. J Am Acad Orthop Surg. 2018 Feb 1. 26 (3):75-82. [View Abstract]

Supernumerary digit, no magnification.

Supernumerary digit, no magnification.

Twenty-eight-day-old supernumerary digit, connective tissue and epidermis (40x).

Twenty-eight-day-old supernumerary digit, nerve bundle base (40x).

Twenty-eight-day-old supernumerary digit, rudimentary nail unit cartilage (2x).

Twenty-eight-day-old supernumerary digit, rudimentary nail unit cartilage (2x).

Twenty-eight-day-old supernumerary digit, nerve bundle base (40x).

Twenty-eight-day-old supernumerary digit, connective tissue and epidermis (40x).

Supernumerary digit, no magnification.