Single bilateral interdigital flexion crease of the fifth finger in a phenotypically normal male

Introduction The wrist, thenar, palmar, and digital flexion creases represent skin flexion lines in the vicinity of synovial joints, where the skin is attached to the underlying fascia [1]. Digital creases ease movement of the digits without impingement by providing “folding points” in the skin analogous to the creases in a folded roadmap, and due to strong attachments to the underlying fascia, they also provide the stability to the skin required for strong grasping. Two digital flexion creases are normally present on the thumb (metacarpophalangeal and interphalangeal creases) and three of them on the other fingers (metacarpophalangeal, and proximal and distal interphalangeal creases). A ring crease, usually present as a metacarpophalangeal crease on the third finger and fourth finger, is hardly ever found on the fifth finger [2]. Different variants in the digital flexion creases are featured in a number of syndromes. Excessive digital creases have been found in partial deletions of chromosome 1q [3], partial trisomy of 13q [4] and 14q [5], cerebro-oculo-facio-skeletal (COFS) syndrome [6], as well as in sickle cell anemia [7]. A reduced number of digital flexion creases has been described in Down syndrome (often accompanying single transverse palmar crease) [8], Edwards syndrome [9], fetal alcohol syndrome [10] and in some disorders involving digital joint flexion restrictions. Both excessive and reduced numbers of digital flexion creases can be found in patients with Larsen syndrome [11]. While extra interphalangeal transverse creases of the fifth finger can be found in phenotypically normal males and females without radiographic abnormalities of the bones and joints or evidence of dyskinesia [12], the presence of missing digital crease is extremely rare in individuals without chromosomal or other anomalies. For the first time in the medical literature we report a case of a single interdigital flexion crease of the fifth finger present bilaterally in a phenotypically normal male individual.