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Introduction
Melasma is an acquired hyperpigmentary skin disorder characterized by irregular light to dark brown macules occurring in the sun-exposed areas of the face, neck and arms.
Epidemiology
The prevalence of melasma varies according to ethnicity, sunlight
intensity and skin phototype. Melasma most commonly affects Fitzpatrick skin
phototypes III-V. The condition is more common in women than in men. This is rare
before puberty and common in women during their reproductive years. Melasma
occurs most commonly with pregnancy (chloasma) and with the use of
contraceptive pills.
Epidemiological studies reported higher prevalence of melasma in Middle
Eastern, East Asian (Japanese, Korean, and Chinese), Indian, Pakistani and
Mediterranean-African populations. The prevalence rate in the Southeast Asian
population is 40%.
Pathophysiology
The pathophysiology of melasma involves various factors that lead to enhanced melanin production, such as proopiomelanocortin production, melanocortin-1 receptors (MC-1R) on the melanocyte surface, protein kinase-C activation from diacylglycerol secretion, cGMP pathway triggered by the release of nitric oxide and increased cytokine and subsequent growth factor production.
Risk Factors
Solar and ultraviolet (UV) exposure (eg high-energy visible light, long-wave UVA [UVA-1]) is the most important factor in the development of melasma. Risk factors may include pregnancy, the use of oral contraceptives or hormone replacement therapy, and family history of melasma. Other factors implicated in the etiopathogenesis of melasma are photosensitizing medications (eg non-steroidal anti-inflammatory drugs [NSAIDs], Acetamoniphen, cardiovascular drugs, antineoplastic agents, antiepileptic agents, antibiotics, prostaglandin analogs), genetic factors (eg Val92Met genotype of the MC1R gene, vitamin D receptor gene polymorphism [TaqI], estrogen receptor gene polymorphisms), mild ovarian or thyroid dysfunction, and certain cosmetics.
Classification
Clinical Classification of Melasma
Based on clinical pattern, melasma may be classified as: Centrofacial,
which is the most common type with macules and patches on the cheek, forehead,
upper lip, nose and chin; malar, which appears on the cheeks and nose; and
mandibular lesions, which are seen over the ramus of the mandible where the
pigment may also have a bluish appearance.
Histological Classification of Melasma
Melasma_Disease BackgroundEpidermal
An epidermal melasma appears as light brown with enhancement of pigmentation under Wood’s light. The melanin increases in the basal, suprabasal and stratum corneum layers with highly dendritic and pigmented melanocytes. The epidermal pigment is more amenable to treatment than dermal pigment.
Dermal
A dermal melasma appears as ashen or bluish-gray with no enhancement of pigmentation under Wood’s light. Perivascular melanophages on the superficial and deep dermis with less hyperpigmentation are seen in the epidermal layer.
Mixed
A mixed type of melasma appears as dark brown with enhancement seen in some areas only. Melanin deposition is found in the epidermis and dermis. This is the most commonly reported (23-80%) type of melasma.
Indeterminate
An indeterminate melasma is inapparent under Wood’s light. The melanin deposition is found in the dermis and the pigment is not discernible in dark skin. This is seen in Fitzpatrick’s skin phototype V-VI.