The Histopathology of Melasma in Brown Skin

Abstract

Racial variations exist in the distribution of melanin and melanosomes in the epidermis; however, no racial differences are observed in melanocyte density and concentration. Melanosomes in pigmented skin are distributed in the entire epidermis unlike in fair skin where only few melanosomes are found in the basal and malpighian layers. Studies on melasma in brown skin consistently show increased epidermal melanocytes and melanin in all the layers of the epidermis accompanied by solar elastosis and mild perivascular infiltrate. The presence of melanophages is a variable observation and raises the question whether there is indeed a “dermal” type of melasma. Important clinical differential diagnoses include ochronosis, dermal melanocytosis, ashy dermatosis (AD), erythema dyschromicum perstans (EDP), lichen planus pigmentosus (LPP), Riehl’s melanosis, and minocycline pigmentation, which are conditions mostly observed in Fitzpatrick skin type IV brown skin. A skin biopsy is indispensable when melasma presents with unusual clinical features or has become recalcitrant to treatment. It may be useful to establish the nature and pathology of facial hyperpigmentation and determine changes in the underlying dermis which may provide clues to the diagnosis.