CASE #1: Accessory digits
Polydactyly is the most common congenital digital anomaly of the hand. The three types of this condition are: (1) type I, in which the extra finger is a soft small tissue segment (post-axial nubbin); (2) type II, in which the extra finger includes bone, tendon, and cartilage without any joints; and (3) type III, in which the extra finger is fully developed with own metatarsal and is a complete, functioning digit.1 Some patients have accessory toes as well as fingers, but most have either one or the other.
An accessory digit most commonly appears as a solitary finding. This patient was most likely a case of autosomal dominant disease with incomplete penetrance (only about 30% of patients will have a positive family history for polydactyly or sporadic inheritance). Duplications occur bilaterally in about 40%-50% of patients, but these are often not symmetric.
Extra digits occur most commonly on the ulnar side of the hand (postaxial polydactyly), less commonly on the radial side (preaxial polydactyly), and very rarely on one of the middle three digits (central polydactyly).2,3 Central polydactyly is often inherited with an associated syndactyly, a condition in which two or more digits are fused together. The extra digit is most commonly an abnormal fork of one of the five digits. Rarely, the extra digit may originate at the wrist as a normal digit does.
Polydactyly is a finding of 267 syndromes listed in Online Mendelian Inheritance in Man (available at www.ncbi.nlm.nih.gov/omim, accessed July 15, 2011), a database of human genes and genetic disorders, and syndromic polydactyly is commonly an autosomal recessively inherited trait.4 Because hand and foot polydactyly are associated with congenital defects in 23.4% of patients, a genetic workup and thorough medical examination should be performed in these patients.
A number of syndromes include polydactyly as a finding: acrocallosal syndrome, basal cell nevus syndrome, Bardet-Biedl syndrome, Biemond syndrome, ectrodactyly-ectodermal dysplasia-cleft lip/palate syndrome, Ellis van Creveld syndrome, Hirschsprung disease, unilateral renal agenesis, hypertelorism, congenital deafness, Meckel Gruber syndrome, Joubert-Boltshauser syndrome, Laurin-Sandrow syndrome, McKusick-Kaufman syndrome, mirror hand deformity (ulnar dimelia), Mohr syndrome, oral-facial-digital syndrome, Pallister-Hall syndrome, Rubinstein-Taybi syndrome, Smith-Lemli-Opitz syndrome, short rib polydactyly, trisomy 13 and 21, tibial hemimelia, VATER association (Vertebral [defects], [imperforate] Anus, Tracheoesophageal [fistula], Radial and renal [dysplasia]).5
Polydactyly has an incidence of one in every 500-1,000 live births. Postaxial hand polydactyly is a common isolated disorder in African black and African-American children, and autosomal dominant transmission is the likely mode of inheritance. Postaxial polydactyly is approximately 10 times more frequent in blacks than in whites and is more frequent in male children. Among blacks, polydactyly occurs in about four of 1,000 births, compared with 0.3 to 1.3 out of 1,000 births among whites. Polydactyly appears to be slightly more common in males. In contrast, postaxial polydactyly seen in white children is usually syndromic and associated with an autosomal recessive transmission.
Diagnosis of polydactyly can be made in utero with ultrasound. A radiologist can identify fetal finger buds utilizing transvaginal ultrasound as early as 9 weeks’ and reliably by 13 weeks’ gestation.6,7 If polydactyly is noted, conduct a through examination of the heart, nervous system, limbs, and kidneys to identify associated syndromes. Skeletal dysplasias can be linked to polydactyly (i.e., short rib polydactyly). Follow-up ultrasound between 17-34 weeks with biometric profile can establish the diagnosis of isolated polydactyly.
Histologic examination postaxial or preaxial nubbin tissue resembles the histology of a congenital traumatic neuroma and demonstrates hyperkeratosis and acanthosis overlying many nerve bundles in the dermis. Abundant Merkel cells8 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.9
If a type I polydactyly is present at birth and x-ray shows no bone in the post-axial duplicated digit, the postaxial nubbin can be removed through suture ligation in the newborn nursery. It should be noted that suture ligation is not usually performed in older infants.10-12 Suture ligation of supernumerary digits with residual cartilage and/or an underlying duplicated metatarsal will lead to future deformity.13 If type II or type III polydactyly is present, a surgeon can perform formal amputation after x-rays are taken to ensure that there are no underlying deformed metatarsals, in which case the supranumerary digit should be surgically excised. Postponing excision until age 9 to 12 months is advisable to decrease anesthesia risk. Adequate web space should be preserved and the digit removed.
As the digits did not affect the health of the patient, it was decided to leave them in place. A complete physical showed no systemic findings related to the accessory digits.