Skin nontumor
Pigmentary disorders
Melasma
Author: Christopher S. Hale, M.D.
Last author update: 1 April 2013
Last staff update: 28 August 2020
Copyright: 2002-2023, PathologyOutlines.com, Inc.
PubMed Search: Melasma skin
Table of Contents
Definition / general | Terminology | Clinical features | Treatment | Clinical images | Microscopic (histologic) description | Electron microscopy description | Differential diagnosisCite this page: Hale CS. Melasma. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/skintumormelanocyticmelasma.html. Accessed March 21st, 2023.
Definition / general
- Acquired large areas of darkened skin, usually due to hormonal changes (birth control pills, pregnancy) and usually on both sides of face (eMedicine)
- Clinical patterns are centrofacial, malar and mandibular
- Classification (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
Terminology
- Also called chloasma
Clinical features
- 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;8:3)
- Some cases associated with phenytoin, autoimmune thyroid disease, UV light in men (J Am Acad Dermatol 2012;66:642)
- May be due to increase in stem cell factor and c-kit expression (Br J Dermatol 2006;154:1094)
Treatment
- Avoid sunlight, broad spectrum (UVA + UBV) sunscreen
- Also topical hydroquinone, tretinoin, azelaic acid and Vitamin C
- Also laser (J Cosmet Laser Ther 2008;10:167), pidobenzone 4% (Dermatol Ther 2008;21:S18), chemical peels (Dermatol Surg 2008;34:1032), ellagic acid containing products (J Dermatol 2008;35:570) or Mequinol 2% / tretinoin 0.01% topical solution for men (Cutis 2008;81:179)
- Often relapses when treatment stops
Clinical images
Images hosted on other servers:
Confluent hyperpigmented macules in a malar distribution
Microscopic (histologic) description
- 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 description
- More melanosomes in keratinocytes, melanocytes and dendrites
Differential diagnosis
- Broad clinical differential (Dermatol Clin 2007;25:321)
- Actinic lichen planus
- Cutaneous mercury deposits
- Erythema dyschromicum perstans: ashy dermatosis
- Exogenous ochronosis: history of hydroquinone use
- Hori nevus: acquired bilateral nevus of Ota-like macules
- Lichen planus pigmentosus: uncommon variant of lichen planus characterized by hyperpigmented, dark brown macules in sun exposed areas and flexural folds
- Pigmented contact dermatitis (Riehl melanosis)
- Post inflammation pigmentation
