Skin - Melanocytic tumor
Other melanocytic lesions
Melasma

Author: Christopher Hale, M.D. (see Authors page)

Revised: 22 February 2017, last major update April 2013

Copyright: (c) 2002-2017, PathologyOutlines.com, Inc.

PubMed Search: Melasma skin

Cite this page: Melasma. PathologyOutlines.com website. http://pathologyoutlines.com/topic/skintumormelanocyticmelasma.html. Accessed May 29th, 2017.
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
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