Linea Nigra: Case Report of a Woman With a Pregnancy-Associated Linear Streak of Cutaneous Hyperpigmentation on Her Abdomen From the Umbilicus to the Pubic Symphysis.

Linea nigra is a distinctive presentation of asymptomatic cutaneous hyperpigmentation on the abdomen that usually extends from the umbilicus to the pubic symphysis. It is frequently observed as a physiologic change associated with pregnancy. A primigravida 19-year-old woman began to develop skin darkening during week 24 of gestation. She delivered a healthy infant. Three months postpartum, the hyperpigmentation had not resolved. After the benign characteristics of her cutaneous hyperpigmentation were explained, the patient decided to clinically monitor the dark linear streak. Similar to this patient, clinical studies of pregnant women have observed the incidence of pregnancy-associated linea nigra to range from 32% to 92%; in contrast to this woman, partial or complete spontaneous resolution of the skin darkening commonly occurs after delivery of the newborn. During gestation, the development of linea nigra has been postulated to be caused by elevated estrogen, progesterone, and/or melanocyte-stimulating hormone levels. Linea nigra is not restricted to gestational females; it has also been noted in newborns and children. In addition, it has also been observed in men who had either benign prostate hyperplasia or prostate cancer. In summary, linea nigra is often an acquired longitudinal streak of benign cutaneous hyperpigmentation on the abdomen; when linea nigra is pregnancy-associated, the skin darkening often partially or completely resolves, spontaneously after delivery.