Intrauterine big toenail imprints: A new cause of congenital skin dimples

Abstract

Congenital skin dimples (SD) are small cutaneous depressions that can be noted on any part of the body and may be caused by traumatic, mechanical, metabolic, and genetic factors as well as by exposure to infections or drugs. We describe 3 cases of unrelated healthy newborns displaying SD and discuss as a possible explanation the persistent friction of the big toenail onto the immature skin of the fetus during intrauterine life causing as depression in the skin. | 227Pediatric Dermatology BRIEF REPORT caused by a variety of factors. 1 Largely reported in the literature are SD due to accidental trauma during amniocentesis. 2 Other known mechanical causes of SD are represented by intrauterine factors such as bicornuate uterus, uterine scars, or multiple pregnancy; typically, these factors result in more widespread and irregular scars, such as amniotic bands or aplasia cutis congenita with fetus papyraceus. SD located in the acromial, sacral, and sacrococcygeal area, as well as on the limbs, face, and over joints may be inherited as a single trait or related to more complex genetic syndromes, such as 18q syndrome. Additionally, there are reports connecting SD to severe infections during pregnancy, particularly rubella, inborn metabolic errors and drug exposure. In our cases, a genetic or systemic condition was reasonably excluded, and there was no history of amniocentesis. Lacking a convincing alternative explanation, we noticed that the morphology and the alignment of the dimples fit perfectly with the margin of the opposite foot when we leaned the big toenail against the area of the dimples. It could be argued that chronic microtrauma by toenails during intrauterine life may play a role in the genesis of the dimples, especially after 36-37 weeks of gestation, when the fetus loses adequate room for movement. At this point in gestation, the keratinization process of nails has already taken place and repeated contact with the fragile skin in the same area could potentially cause permanent damage. Immature skin is known to be prone to scar formation from minor trauma 3 as evidenced by premature neonates who may develop scars from routine medical procedures, such as the placement of electrocardiographic leads. 4This hypothesis of toenail impingement on the skin during gestation may provide a simple explanation for otherwise unexplained SD in healthy infants.