Acquired Unilateral Melanocytic Nevi in Otherwise Normal Skin

Abstract

We describe a case with numerous melanocytic nevi in otherwise normal skin. A 5-year-old girl presented with more than 100 small pigment lesions on her left arm, shoulder and upper back without underlying light brown macule. The pigment lesions were first found on her left forearm at 3 months old and gradually increased along with her growth. Skin biopsy from a pigmented lesion shows a pathological change in compound-type melanocytic nevus without any atypical changes. Speckled lentiginous nevus is known to have multiple melanocytic lesions on the underlying brown macule from birth. Partial unilateral lentiginosis is characterized by unilateral lentigines with histopathological changes in lentigo but not melanocytic proliferation in the dermis. Agminated melanocytic nevi tend to be clustered together in a circumscribed area, whereas in the present case melanocytic nevi were segmentally arranged but not agminated. We consider that this is an unusual type of mosaicism of melanocytic disorders.

Melanocytic naevi clustered on normal background skin

“…MM have been reported to occur on all types of segmentally arranged melanocytic naevi, other than SN and SCMN. 5,6,12,18,19,[22][23][24] While this occurrence is not unexpected for mosaic DNS, there is not enough evidence to believe that the involved cutaneous segments carry a significantly increased risk of malignant degeneration.…”

“…In two cases, MM occurred within the involved segment, while in another case, BN were also present . One patient also had an ipsilateral achromic naevus . Genetic testing was carried out on only one case, and showed a mosaic mutation of BRAF …”

“…15 One patient also had an ipsilateral achromic naevus. 22 Genetic testing was carried out on only one case, and showed a mosaic mutation of BRAF. 23 BN, SN and CAMN occur clustered on a skin segment, most often in an agminated shape.…”

Blaschkolinear Congenital Melanocytic Nevus

“…This hypothesis is not yet supported by a molecular study. Nonetheless, even though demonstrated in a keratinocytic model, a recent study identified a putative molecular basis of linear nonepidermolytic, nonorganoid keratinocytic epidermal nevi [8] . In this study, linear epidermal nevi could be linked to postzygotic mutations in the fibroblast growth factor receptor 3 gene (tyrosine kinase receptor), which occurred in a single keratinocyte stem cell at an early stage of the embryonic development [9] .…”

“…A recent case of acquired numerous melanocytic nevi arranged in a linear pattern on the left arm has been described and considered as an unusual type of mosaicism of melanocytic disorders [8] . The concept of mosaicism could give an attractive explanation of the linear distribution of the nevus as observed in our case and those of Happle and Effendy [6] .…”