WHAT IS THIS PAPULE?
A 26-year-old Hispanic patient presented with a lifelong history of stubs growing off of both of his little fingers. A physical examination revealed that his fingers and toes were of normal length and fully functional. His skeletal structure, including his ribs and clavicle, also was normal. A chest X-ray taken the previous year to rule out pneumonia showed that all of his ribs were normal. The papules on his fingers were asymptomatic and have not changed in appearance since birth. The patient was not selfconscious or concerned about these lesions. He was otherwise in good health with no pertinent medical, family or social histories.
WHAT’S YOUR DIAGNOSIS?
Diagnosis: Bilateral Ulnar Accessory Digits
The presence of polydactyly can be an isolated and idiopathic, but it can also be associated with certain syndromes. Some common associations of postaxial polydactyly are Ellis-van Creveld disease, Jeune syndrome, Meckel syndrome (also known as Meckel-Gruber syndrome), Bardet-Bield syndrome, Smith-Lemli-Opitz syndrome, trisomy 13, polydactyly-hydrometrocollpos syndrome, Weyer acrofacial syndrome, Opitz C syndrome, Sugarman syndrome, Biechoud syndrome, and Oliver syndrome.
As it is clearly visible, the differential diagnosis for polydactyly is quite extensive. Therefore to determine the exact cause of the polydactyly, a medical history, a physical examination, and diagnostic tests are needed.1
Polydactyly has been observed throughout history. In 1896, in their books, Anomalies and Curiosities of Medicine, George Gould and Walter Pyle documented the presence of polydactyly during the Babylonian Chaldean dynasty in 6th century B.C.2
Although many incidences of polydactyly have been identified, determining the cause for this condition took time to develop. In his book System of Nature, in 1751, Pierre-Louis Moreau de Maupertuis documented over several generations the incidences of polydactyly and concluded that the polydactyly trait could be passed on by both males and females and that heredity was due to the presence of a mutation in some particle in the germ cells.3,4
Since then, major advances have been made in research, and the cause of polydactyly has been identified in mutations of four different loci.
Polydactyly, the most common congenital hand malformation, is a type III anomaly according to the International Federation for Societies for Surgery of the Hand (IFSSH), which classified clinical problems of the hand into seven groups.5
Polydactyly can be divided into radial (preaxial), center, and ulnar (postaxial) polydactyly.6
Radial polydactyly is the presence of an accessory digit on the lateral aspect of the hand or the medial aspect of the foot.
Center polydactyly involves the medial or lateral aspect of the central three fingers. It has been shown that postaxial polydactyly, which is the focus of this discussion, occurs more frequently than either radial polydactyly or center polydactyly, which is very uncommon.6
Postaxial polydactyly is the presence of an accessory digit on the medial aspect of the hand or the lateral aspect of the foot.
Ulnar (Postaxial) Polydactyly
The incidence of postaxial polydactyly is variable among racial groups. It has a greater prevalence among the Black population, occurring approximately 10 times more frequently when compared to the Caucasian population (reference). The frequency in the Black population is between 1/300 to 1/100 live births. In the Caucasian population, incidence rates occur from 1/3,330 to 1/630 live births. Type B Temtamy and Mackusick postaxial polydactyly has approximately a 65% penetrance. Type A postaxial polydactyly has a much higher penetrance.7
Postaxial polydactyly occurs either in conjunction with another syndrome or as an isolated case. When in conjunction with other syndromes, it has been seen to exhibit both autosomal dominant and autosomal recessive forms of inheritance. Ellis-van Creveld syndrome, for example, is inherited as an autosomal recessive trait.8
As an isolated inheritance pattern, postaxial polydactyly is passed on in an autosomal dominant fashion. In about 75% of the chromosomal cases, postaxial polydactyly is associated with trisomy 13.7 There are currently four loci that have been determined to be the cause for isolated postaxial polydactyly. The first, PAPA1, is a mutation in the GLI3 regulatory gene on 7p13.6. The second locus, PAPA2, is located on 13q21-q32 and is prevalent among the Turkish people. This locus only expresses the Temtamy and Mckusick Type A postaxial polydactyly. The third locus, PAPA3, is on 19p13.1-13.2 and its mutations have been expressed among the Chinese. The fourth locus is located on 7q21-q34. Aside from PAPA2, these loci account for both.9
As mentioned previously, postaxial polydactyly is much more common than radial polydactyly.10 Stelling and
Turek originally classified postaxial polydactyly into three types. Type I postaxial polydactyly is the appearance of an appendage. Type II is a partial duplication of the small finger. Type III is a complete duplication that includes a duplicate metacarpal.
Another classification of postaxial polydactyly was proposed by Temtamy and Mckusick,6 who divided the anomaly into types A and B. Type A postaxial polydactyly encompasses those with a well-formed accessory digit that either articulates with the fifth metacarpal or a duplicated metacarpal. Type B postaxial polydactyly consists of a less-developed accessory digit. A rudimentary polydactyly can be seen in some patients. These are vestiges of the accessory digit after surgery and are histologically similar to traumatic neuromas.
After reviewing 148 patients with postaxial polydactyly, a new classification was proposed by Rayan that segregated the anomaly into five types.10 Type I is a small protuberance from the skin that contains no bone. Type II is the presence of a small accessory digit with a small nail and bone, which does not articulate with the fifth metacarpal. Type III postaxial polydactyly is a more developed version of Type II. The middle phalanx or, if present, the proximal phalanx of the accessory digit articulates with a bifid fifth metacarpal. Type IV postaxial polydactyly is a fully developed accessory digit that has its own metacarpal. Lastly, Type V is when syndactyly is associated with postaxial polydactyly.
The classification system proposed by Rayan is a relatively new concept and therefore, the Temtamy and Mckusick classification of postaxial polydactyly is still the more widely-used system today.
Diagnosis and Treatment
An isolated case of polydactyly is not a harmful condition and poses no risk to the physical health of an individual. Therefore the only treatment available is surgery and is done mainly for cosmetic reasons.
The patient described was diagnosed histologically; a shave biopsy was done to remove one of the papules, and the accessory digit were simply treated with shave excisions.
The standard surgical procedure for treatment of postaxial polydactyly is suture ligation at the base of the accessory digit. This procedure is simple; however, many post-surgical patients develop rudimentary polydactyly, which would warrant a second surgical excision.11
Aiming to decrease the frequency of post-surgical rudimentary polydactyly formation, Leber and Gosain proposed a new surgical procedure involving the high transection of the accessory digital nerve. The underlying principle of this procedure is never to cut, ligate, or burn a nerve at the skin level. Doing so would cause the axon to regenerate in an unorganized manner. This technique requires general anesthesia and begins with an elliptical incision along the long axis of the accessory digit. The accessory digital nerve would then be dissected free from its surrounding tissue and cut, dividing the accessory digital nerve into a proximal portion and a distal portion. The proximal portion would then be retracted into the bed of healthy soft tissue. A follow-up of patients from 2 to 6 years gave excellent results. Although it is still possible for neuromas to develop more than 6 years post-surgery, development is highly unlikely because nerve regeneration usually occurs within the first year after injury.
Polydactyly, when associated with other syndromes, is more complicated. Simple surgical treatment does not completely heal the individual. Lab tests and physical examinations need to be done to determine the syndromes that the polydactyly phenotype is associated with and to treat it accordingly via multidisciplinary approach.
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