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MELASMA
MELASMA
Melasma is a common pigmentary disorder. The nomenclature is Greek from the word melas (black), as it manifests clinically as symmetric hyperpigmented macules on photo-exposed areas. It is more common in darker skin types (Fitzpatrick skin types IVโ VI), especially in people of Asian and Hispanic origin who live in areas with high sun exposure.1 It typically affects women of reproductive age, with prevalence in men being much lower.1,2
Etiology
Although several factors have been implicated in the etiology of melasma, it remains incompletely understood. The main causative factors include ultraviolet (UV) radiation, hormonal factors (pregnancy and oral contraceptive pills), and genetic predisposition. Other possible contributors include cosmetics, photosensitizing drugs, thyroid disease, ovarian tumors, and stressful events.1 It is hypothesized that in a genetically predisposed person, development of melasma depends on the interaction between environmental and hormonal influences. Melasma has been reported in identical twins, and many patients have an affected family member.3 Some drugs such as phenytoin, griseofulvin, NSAIDs, finasteride, and imatinib have been implicated to cause melasma-like pigmentation.1,4,5
Pathogenesis
UV radiation causes cell membrane damage along with peroxidation of its lipids leading to the generation of reactive oxygen species (ROS), stimulating melanogenesis. Infrared and visible light also play a role in the development of melasma. Circulating estrogen binds to estrogen receptors present on melanocytes leading to melanogenesis and subsequent pigmentation.6 The number of melanocytes within involved areas may be normal or increased. Melanosomes within affected melanocytes are increased in size.
Clinical features
Melasma presents clinically with symmetrical hyperpigmented macules present predominantly on sun-exposed areas. The face is the most commonly affected site; rarely, there may be involvement of other areas such as the neck or forearms.