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Skin-Melanocytic tumors
Melasma
Author: Nat Pernick, M.D., PathologyOutlines.com, Inc.
Revised: 5 July 2009, last major update November 2008
Copyright: (c) 2005-2009, PathologyOutlines.com, Inc.
Definition
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● Acquired large areas of darkened skin, usually due to hormonal changes (birth control pills, pregnancy), usually on both sides of face
Terminology
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● Also called chloasma
Epidemiology
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● 90% women; more common in dark-skinned individuals
● In pregnant women, hormones cause “mask of pregnancy” on face and darkened skin on abdomen and elsewhere
● Associated with freckles, lentigines and 4+ nevi (BMC Dermatol 2008 Aug 5;8:3)
Classification
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● Based on level of increased melanin in skin determined by Wood’s light examination (J Am Acad Dermatol 1981;4:698)
● Epidermal: 70% of cases, increased melanin in basal and suprabasal epidermis; skin pigmentation enhanced under Wood’s light; responds best to bleaching agents
● Dermal: 10% of cases, increase in melanophages in upper dermis; no enhancement of skin pigmentation under Wood’s light, responds poorly to bleaching agents
● Mixed: 20% of cases, mixture of epidermal and dermal features; patchy enhancement of skin pigmentation under Wood’s light
● Indeterminate: 2% of cases; not possible to characterize pigmentation pattern
● Clinical patterns: centrofacial, malar, mandibular
Treatment and prognosis
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● Avoid sunlight, broad spectrum (UVA + UBV) sunscreen
● Also topical hydroquinone, tretinoin, azelaic acid, Vitamin C
● New reports suggest combination therapy with laser (J Cosmet Laser Ther 2008;10:167), pidobenzone 4% (Dermatol Ther 2008;21 Suppl 1:S18), chemical peels (Dermatol Surg 2008;34:1032), ellagic acid containing products (J Dermatol 2008;35:570), Mequinol 2%/tretinoin 0.01% topical solution for men (Cutis 2008;81:179)
● Often relapses when treatment stops
Clinical images
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Melasma Various images
Micro description
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● Mild lymphohistiocytic infiltrate in 75%
● Increase in epidermal melanin, but no increase in number of melanocytes
● Melanocytes are larger with prominent dendrites (Am J Dermatopathol 2005;27:96)
Electron microscopy
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● More melanosomes in keratinocytes, melanocytes and dendrites
Differential Diagnoses
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● Post inflammation pigmentation
● Pigmented contact dermatitis
Additional references
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End of Skin-Melanocytic Tumors > Melasma
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