Aberrant muscular hyperplasia of the hand and PIK3CA related overgrowth spectrum disorders. A case series study.

Introduction Congenital muscular hyperplasia of the hand is a rarely described entity, characterized by the presence of aberrant or accessory muscles in the hypothenar eminence, which has been always reported as sporadic anomaly in the medical literature. The aim of this paper is to report a series of cases with a phenotype of aberrant muscle hyperplasia associated with PIK3CA mutations. Material and methods We describe a retrospective series of cases followed at our institution between 2008 and 2020, with a unique phenotypein the context of PIK3CA mutations. Results A total of 6 patients were included (4 males and 2 females), who presented with an enlargement of the hypothenar eminence of the hand and peculiar wrinkling of the overlying skin, associated with ulnar deviation of the metacarpo-phalangeal joints. In all cases, variable degrees of congenital overgrowth of the ipsilateral limb were observed. Skin punch biopsy (5 mm diameter and 3-5 mm depth) was performed on 4 patients, where striated muscle hyperplasia and the presence of striated muscular fibers in the dermis and hypodermis were observed in all of them. Genetic studies revealed PIK3CA mutation in 3 of the 4 patients whose affected tissue was analyzed, in a mosaic state ranging from 3 to 8% (His1047Arg, Glu542Lys, and Cys420Arg, 1 case each). Conclusion Aberrant muscular hyperplasia of the hand is a well-recognized entity scarcely described in association with PIK3CA spectrum disorder in the pediatric population. The role of PIK3CA in muscle overgrowth is not yet well understood.