Background 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).
Objective 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.
Results 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).
Conclusion 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.
Linea nigra (LN) (Fig. 1), 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.1
Estrogens mediate their activity by interacting with and activating specific intracellular receptor proteins – estrogen receptors α and β 3.2,3
These receptors are found in different organs, particularly the skin. Estrogens have significant effects on keratinocytes, fibroblasts, and melanocytes. A previous study referred to above1 showed that
• The incidence of LN varied in different genders, age groups, and certain clinical status such as pregnancy and, in men, benign prostatic hyperplasia (BPH)/prostate carcinoma (PC) (Fig. 2). Following a striking drop in the incidence of LN in clinically normal men, the incidence increased dramatically in patients with BPH and PC. It would appear that hormonal influences are related to LN in these male conditions. Modification of the prostatic epithelium has been suggested as the cause of feminization in these clinical conditions.4
• LN was present in 80% of the few men aged above 50 years who had BPH/PC.LN increased with age in children reaching a peak of 45% between 11 and 15 years of age (Fig. 2).
• LN was seen in 92.0% of pregnant versus 16.0% of non-pregnant adult females.
Aims and objective of current study
BPH is a common problem in the aging man. PC is the commonest adult male neoplasm in Nigeria.5 Increased estrogen or lack of sensitivity of androgen receptors has been suggested as a possible factor.1
• Finger length ratio has been suggested as a simple clinical tool that can help in determining prostate cancer risk.6,7 We decided to embark similarly on a clinical feature that could help in avoiding costly diagnostic procedures in a resource-poor area such as Nigeria.
• We decided to look at LN, a clinical feature readily accessible on the abdomen, checking the prevalence of LN in patients with BPH or PC, two conditions that appear to be hormone-sensitive disorders.
• We also looked for evidence of a purported increase in peripheral estrogens such as the pattern of pubic hair and presence of gynecomastia in the study populations in the hope of increasing diagnostic capability.
Subjects and methods
The study was carried out at the urology clinic of the University College Hospital (UCH) Ibadan, Nigeria between November 2008 and December 2009. Fifty patients had BPH and 25 had PC; 45 with urethral stricture and other medical problems, excluding BPH and PC, were used as controls. Demographic data about age, drug use, surgical operations, etc. were collected. Subjects, including controls, were examined generally and specifically for the presence of LN, gynecomastia, and pubic hair pattern. The patients and controls were examined by a dermatologist for the presence of LN. Blood prostate specific antigen was assayed. PC was confirmed by histology.
SPSS version 16 was used to analyze data. Descriptive statistics frequency, percentages, etc. were used to summarize the data. Associations between variables were assessed using the χ2 test. The statistical level of significance was considered at P < 0.05.
The results are summarized in Table 1. LN was found in 48% of PC, 26% of BPH and 8% of controls (Fig. 3). Female pubic hair pattern 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 (Fig. 4).
Table 1. Prevalence of linea nigra, gynecomastia, and female pubic hair pattern
Benign prostatic hyperplasia (n = 50) (%)
Prostate carcinoma (n = 25) (%)
Controls (n = 45) (%)
Female pubic hair pattern
For the 50 patients with BPH, the 25 patients with PC, and the 25 patients with other urologic conditions medians and interquartile ranges for age, and numbers and percentages for gynecomastia, pelvic hair distribution, and LN in all cases, differences between groups were deemed inexplicable by chance (P < 0.05 for each analysis).
Age, gynecomastia, pelvic hair distribution, and LN were entered into multinomial logit regression. Back step regression found gynecomastia the sole important explanatory variable.
Differences with respect to gynecomastia between patients with PC and BPH were deemed inexplicable by chance (P = 0.008, Fisher exact test).
Differences between patients with BPH and patients with conditions other than BPH or cancer were deemed explicable by chance (P = 0.17, Fisher exact test).
In developing countries, provision of “quality health at an affordable cost” becomes an important maxim. In light of this, the potential for diagnosis of PC the commonest male neoplastic disease in Nigeria, thus provides hope and a guideline for the type of research that can help in the management of this fatal disease.
In the current study, however, it would appear that LN could not be used solely to diagnose PC or to distinguish BPH from PC (Fig. 5).
Many patients were not aware of LN on their abdomen thus it is difficult to tell whether it is the effect of hormonal therapy or orchidectomy. Furthermore, LN was seen even in patients with BPH who were certainly not on hormonal therapy and who had not undergone orchidectomy.
A further study is indicated to show whether the relation of gynecomastia, LN, and pelvic hair distribution to PC is only found in patients who had undergone bilateral orchidectomy. Such a study could confirm the notion that bilateral orchidectomy feminizes patients more so than either BPH or other urologic conditions.
In the study population, the prevalence of LN was the highest (48%) in the group with PC. However, it appears from this study that LN cannot be used as the sole evidence for the diagnosis of PC. Gynecomastia was a better predictor factor as the sole feature in the three population groups studied. Further studies will be needed to characterize the role of LN in this condition in men before and after treatment.