Prevalence of Linea nigra in patients with benign prostatic hyperplasia and prostate carcinoma

Linea nigra (LN) is linear hyperpigmentation occurring from the umbilicus to the pubic symphysis. Although commonly associated with pregnancy (when it is known as linea gravidarum), it has been found in normal male and female individuals, particularly in the younger age group where estrogen or lack of sensitivity of androgen receptors has been suggested as a possible factor. From a previous study the incidence of LN varied in different genders, age groups, and certain clinical status such as pregnancy and, in men, benign prostate hyperplasia (BPH)/prostate carcinoma (PC).

The need to get a clinical feature that can aid diagnosis of PC, the commonest male neoplasm in Nigeria, at an affordable cost prompted us to look at the incidence of LN in three male populations (i.e., one with BPH, one with PC, and a control population unaffected by these two conditions). Gynecomastia and female hair distribution, two features considered hormone related were looked for additionally in the study population. The study was carried out in a teaching hospital in Ibadan, southwestern Nigeria.

LN was found in 48% of PC, 26% of BPH, and 8% of controls. Female pubic hair was found in 48% of PC, 26% of BPH, and 12% of controls. Gynecomastia was found in 36% of PC, 12% of BPH, and 0% of controls. Differences between patients with BPH, PC, and controls regarding incidence of LN and female pubic hair were deemed explicable by chance (P = 0.17, Fisher exact test). Differences between PC and BPH patients with respect to gynecomastia were deemed inexplicable by chance (P = 0.008, Fisher exact test).

LN alone cannot be used to differentiate PC and BPH. Further studies will be needed to characterize the role of LN in these conditions in men before and after treatment.