The cause of PDLs during pregnancy is unknown. Hormonal alterations, regarding estrogen, progesterone, and melanocyte-stimulating hormone (MSH), can be considered. The inciting factors of the pigmentary changes in the pregnancy include fetoplacental hormone production or alterations in clearance, which may increase the plasma availability of hormones, such as estrogens and progesterone4
. In addition, plasma levels of MSH become significantly elevated by the 8 weeks' gestation, presumably as a result of enlargement of the intermediate lobe of the pituitary gland. Moreover, the production of pro-opiomelanocortin, a source of - and - MSH, has been shown in placental extracts5
. The role of hormonal alterations in PDLs is further supported by the report of a nonpregnant woman with type B PDLs, receiving long-term estrogenic medication6
. An amenorrheic woman with type B PDLs and decreased titers of estradiol and elevated levels of follicle-stimulating hormone has also been reported7
. In the latter case, the hormonal changes were different from the changes in sex hormones during pregnancy. However, there still may be a relationship between abnormal levels of sex hormones and PDLs. Our patient exhibited erythematous changes, in addition to the pigmentation, and histopathologic findings showed dilated vessels in the upper dermis. Estrogen-induced changes in small blood vessels occur during pregnancy, and the blood vessels are found to be widely dilated in the superficial dermis. The erythematous changes in our patient may have resulted from the alteration of estrogen levels in pregnancy. Compression of peripheral nerves emerging from S1 and S2 levels by the enlarged uterus and resulting erythema, pigmentation from neurogenic inflammation has also been suggested8
. However, PDLs are not associated with specific symptoms. Furthermore, the involved areas of the anterior thighs and knees in our case do not correspond to the innervation of S1 and S2. To our knowledge, there have been two reports on PDLs with erythematous changes3,8
. Mild basal layer pigmentation was observed in previous reports of PDLs that examined the biopsies, histopathologically8
PDLs are asymptomatic, and therefore, may be overlooked by patients and physicians. Obstetricians, as well as dermatologists, should be aware of this pregnancy-related condition.