Clinical and epidemiological aspects of subtypes of melanocytic nevi (Flat nevi, Miescher nevi, Unna nevi).

The term "melanocytic nevus" comprises a group of clinically and pathologically distinct subtypes. In this prospective clinical study we evaluated the frequency, localization, and age and gender distribution of flat nevi (FN), Miescher nevi (MN), and Unna nevi (UN) in a caucasian population. Nevi were counted in 400 patients, of which 47 had a history of melanoma. Additionally, the patients answered to a detailed UV questionnaire. Flat nevi represented the most common type of melanocytic nevi, with a peak in the 3rd decade of life. They were mostly found on the extremities and on the trunk. Miescher nevi were most common in the 6th decade and were predominantly found in the head and neck region. Unna nevi showed a maximum in the 8th decade and they were mainly situated on the trunk. The counts of all three nevus subtypes were elevated in the melanoma group. Our results confirm that FN, MN, and UN represent melanocytic nevi with distinctive morphological and clinical characteristics. The role of sunlight seems to be more prominent in the pathogenesis of FN. The precise description of FN, MN, and UN may serve as a base for a pathogenetic distinction of subtypes of melanocytic nevi in the future.