Polydactyly is a common congenital anomaly characterized by the presence of extra digits on the hands and/or feet. It can occur as an isolated condition or as part of a syndrome. Polydactyly is typically classified as preaxial, postaxial, or central. Postaxial polydactyly is most frequently observed in African and African–American populations, whereas preaxial polydactyly is more common in Asian populations [1,2].

Tetrapolydactyly, which involves all four limbs, is a rare presentation that can manifest as non-articulated nubbins of soft tissue or fully articulated extra digits involving bone. The condition may occur sporadically or show a familial pattern, often with autosomal dominant inheritance [1-3].

This report describes a rare case of tetrapolydactyly in a female neonate. This case provides valuable insights into the clinical diversity of tetrapolydactyly and underscores the need for ongoing research and documentation.

This study was approved by the Institutional Review Board of Sapporo City General Hospital (R06-064-1132). Written consent was obtained from the patient for the publication of this report including all clinical images.

The patient is a female neonate born at 37 weeks and 5 days of gestation via cesarean section with an Apgar score of 9 at birth. Throughout the pregnancy, the mother attended regular prenatal check-ups, and the fetus was consistently observed to be in good health. Upon delivery, the neonate was found to have polysyndactyly in both hands and feet and was promptly referred to our plastic surgery department for evaluation.

All members of the patient’s immediate family (father, mother, and older brother) were phenotypically normal. A comprehensive examination did not reveal any other congenital abnormalities. The patient was discharged in excellent condition 3 days after delivery.

The left hand had an additional digit with a bony component on the ulnar side. This extra digit had a metacarpal bone budding from the middle part of the fifth metacarpal bone and contained two phalanges (Fig. 1). Similarly, the right hand had an additional digit on the ulnar side with a bony component comprising two phalanges but without bony articulation or connection at its base (Fig. 2).

The left foot had both preaxial polysyndactyly and postaxial polydactyly (Fig. 3). The preaxial polysyndactyly bifurcated at the first metatarsophalangeal joint, with the skin component conjoined distally at the interphalangeal joint. The postaxial polydactyly bifurcated at the level of the metatarsal bone. The right foot showed postaxial polydactyly, with the additional digit branching off at the level of the metatarsal bone (Fig. 4).

At 7 months of age, the patient was diagnosed with Kawasaki disease and received intravenous immunoglobulin therapy. Otherwise, her growth and development has proceeded normally. She underwent surgical intervention for the extra digits at 9 months of age.

The additional digit on the left hand was excised at the metacarpal level, and the abductor digiti minimi was reattached to the base of the fifth proximal phalanx. On the right hand, the floating type digit was removed without complications, ensuring no residual bone or cartilage remained. For the left foot, the preaxial extra digit was disarticulated at the metatarsophalangeal joint, with subsequent joint reconstruction using periosteum. The postaxial extra digit was excised at the origin from the metatarsal bone, followed by reconstruction of the abductor muscle. For the right foot, the postaxial extra digit was removed, and the abductor digiti minimi was reconstructed.

The terminology used to describe polydactyly involving all limbs varies in the literature, with terms such as “tetrapolydactyly,” “polydactyly 24,” “crossed polydactyly,” and “hexadactylism of all four limbs” being used interchangeably [4-7]. Tetrapolydactyly refers to the presence of extra digits on all four limbs, polydactyly 24 emphasizes the total number of digits, while hexadactyly indicates six digits per limb. These variations in terminology underscore the importance of clear and consistent definitions for accurate diagnosis and communication in clinical practice. In our case, the left foot had seven toes, making terms such as polydactyly 24 or hexadactyly inappropriate to describe this condition accurately.

A study by Miura et al. [1] published in 1987 investigated the incidence of tetrapolydactyly in 1,529 patients with congenital extremity deformities and identified polydactyly of the hand in 337 cases, polydactyly of the foot in 131, and polydactyly of both hands and feet in 27. If tetrapolydactyly is defined as true involvement of all four limbs, only 14 of their 27 cases had true tetrapolydactyly. Among those 14 cases, only one pair of hands and one pair of feet exhibited asymmetry, indicating that symmetric involvement is the predominant manifestation.

Radulescu et al. [8] investigated 64 cases of polydactyly at their institution and reported that 41 cases involved the hands, 17 involved the feet, and six involved both hands and feet.

We identified several relevant case reports by searching PubMed and Google Scholar using key terms such as “tetrapolydactyly,” “tetrapolysyndactyly,” and “polydactyly 24.” Careful review of the reference lists accompanying these reports led to the identification of 15 case reports. Four of these reports were excluded because no full-text version was available. The remaining cases are summarized in Table 1 [2-5,8-14], utilizing previously established classification systems for each type of polydactyly: the Rayan and Frey system [15] for ulnar polydactyly, the Venn-Watson classification [16,17] for preaxial polydactyly, and the SAM (syndactylism, axis deviation, and metatarsal extension) classification system [18] for postaxial polydactyly. Combined anomalies were found in only one case, which presented with sacrosciatic notch narrowing, which is a minor anomaly. A family history was present in four cases, with no familial tendency in the remaining cases. Interestingly, all the cases with hand involvement showed a postaxial pattern and three showed an asymmetric pattern. Heptadactyly was observed in two cases, including ours. The coexistence of an asymmetric number in the feet and an asymmetric pattern in the hands is unique to our case.

During this research, we observed that the morphological features of tetrapolydactyly can be distressing for parents. However, physicians can provide reassurance by explaining that combined anomalies are extremely rare and that hand anomalies can often be managed effectively by surgical intervention. By offering this perspective, physicians can help to alleviate parental anxiety and support a more optimistic outlook regarding their child’s condition.

This case of tetrapolydactyly in a female neonate adds to the limited body of literature on this rare condition. Further research is needed to better understand the genetic basis of tetrapolydactyly and to develop standardized management protocols.