Investigation of the relation between the count and dermoscopic features of the melanocytic nevus and the skin colour measured with mexameter

Aim-hypothesis: We aimed to measure main determinant of the skin colour; melanin content by Mexameter and by this way to investigate more objectively the relation between the melanin content and count, diameter and dermoscopic features of melanocytic nevi., we also planned to investigate the relation between local melanin level and local melanocytic nevi count in different anatomical areas. Methods: One hundred and fourty two participants were examined between October 2015 and April 2016. Melanin indexes (MI) were measured by Mexameter in upper, lower, extensor and flexor surfaces of the upper extremities, neck, anterior and posterior parts of the trunk, flexor and extensor surfaces of the lower extremities. Melanocytic nevi, and nevi larger than four mm were counted in each area. Clinically atypical nevi counts on the trunk were recorded. Dermoscopic images of, a total of 1353 melanocytic nevi on the trunks were taken with Fotofinder digital dermoscopy in 142 participants. Dermoscopic paterns and pigmentation properties of the nevi were determined. Relationships betwen MI and melanocytic nevi counts, large melanocytic nevi counts, atypical melanocytic nevi counts, dermoscopic paterns and pigmentation features of the nevi were investigated. Results: Participants were aged between 18 and 50, mean age was 31.9±11.7. There were 72 females and 72 males. Sixty two percent of the participants were of phototype 2 or 3. There were no participants with phototype 1 and 6. Mean MI of the various anatomical areas of each participants were changed between 83.7 and 400.7, the mean was 189.1±24.2. Skin phototypes and MI was significantly related with each other. Total nevi counts range between four and 134, mean total melanocytic nevi count (MNC) was 31.4±55.2. There were significant, negative relationships between mean MI and total MNC, large MNC/total MNC ratio and atypical MNC/total MNC ratio of participants. Similarly, local MI and local MNC were significantly, negatively correlated with each other in lower extremities, extensor surfaces of the upper extremities, lower flexor part of the upper extremities but not correlated on the trunk and neck. On dermoscopic examination, the most frequently seen nevi were the nevi with reticular patern and uniform pigmentation. On posterior part of the trunk, MI was negatively correlated with, reticular-globuler-homogen combined patern nevi, on anterior part of the trunk, positively correlated with reticular patern nevi. On posterior part of the trunk, there were not any relationship between pigmentation features of the nevi and MI, regardless of the patern. On the other hand on anterior part of the trunk, uniform pigmented nevi ratio was increasing significantly as the MI increased. When we put the patern and pigmentation features of the nevi together; on posterior and/or anterior parts of the trunk, MI was significantly, positively correlated with reticular-uniform pigmented, reticular-central hypopigmented and globular-uniform pigmented nevi ratios. However in same areas, MI was significantly, negatively correlated with reticular homogen-eccentric hypopigmented, reticular homogen-multifocal pigmented, reticular globuler homogen- central hypopigmented, and reticular globular homogen-multifocal pigmented nevi ratios. Conclusion: As the melanin decreased in the skin, number of the melanocytic nevi, ratio of the large melanocytic nevi and of the clinicaly atypical nevi were increased. On dermoscopic examination, decrease of the MI associated with a decrease of the ratio of the nevi with single patern and uniform pigmentation, on the other hand associted with an increase in the ratio of the nevi with more than one patern and multifocal and/or eccentric pigmentation variegations. Changes in the MI affects the number of the paterns and diversity of the pigmentation in the same direction. These changes were in line of "benign features" and "atypical features". So, lower levels of melanin level leads to an increase in all parameters of the nevi related with the melanoma risk, ie MNC, large MNC and atypical MNC. However while there is a relation between MI and MNC in extremites, It was interesting to see absence of such a relation on the trunk. Our study provided new evidences to the knowledge about the effects of the skin colour on the melanocytic nevi and provided new contributions by objectively measuring the skin colour, demonstrating the anatomical differences in colour-nevi count relations, and showing the colour effects on dermoscopic features of melanocytic nevi. Key words: Mexameter, melanin index, melanocytic nevus, dermoscopy, atypia