A study of dermal melanophages in childhood nevi. Reassessing so-called “pigment incontinence”
Journal of Cutaneous Pathology
In inflammatory dermatoses, dermal melanophages (MLP) are ascribed to “pigment incontinence,” with melanin “dropping down” from the epidermis. Although this is analogous to the “dropping down” of melanocytic nevus cells (Abtropfung), MLP in ordinary nevi have not been systematically studied—so “pigment incontinence” may not apply to MLP in nevi. A total of 31 childhood nevi identified by pediatricians and family practitioners were evaluated for the distribution of MLP. We tested the hypothesis that a dermal origin of the melanin in MLP is more likely than dropping down from the epidermis. In our cohort, 90.3% (28/31) of childhood nevi had dermal MLP, a significantly higher frequency, compared to 31/60 ordinary adult nevi (P < 0.0001). Superficial dermis was the most common location (P < 0.001). However, only six specimens had MLP restricted to the superficial dermis, significantly less than predicted by the theory that melanin drops down from the epidermis (P < 0.00001). We also evaluated perivascular MLP, since nerves run together with vessels in neurovascular bundles (NVB), and it has been showed that precursors of melanocytes migrate from the neural crest to the skin as nerve sheath stem cells. Superficial NVB MLP correlated with deep NVB bundle MLP (P < 0.05), suggesting that NVB MLP represent “tombstones” for superficial and deep dermal nevus cells. Deep dermal, deep NVB, and deep periadnexal MLP may be valid biological criteria for diagnosis of congenital type (prenatal) nevi. Viewing prenatal nevi in children as a neurocristopathy fits a major principle of pediatric pathology: childhood diseases should be studied and understood based on what happens during tissue development.
Cramer, S., Salgado, C., & Reyes-Múgica, M. (2020). A study of dermal melanophages in childhood nevi. Reassessing so-called “pigment incontinence”. Journal of Cutaneous Pathology, 47 (9), 809-814. https://doi.org/10.1111/cup.13718