Skin melanocytic tumor

Lentigines, melanotic macules and melanocytic hyperplasia

Melanotic macule


Editorial Board Members: Viktoryia Kazlouskaya, M.D., Ph.D., Jonathan D. Ho, M.B.B.S., D.Sc.
Khaled Sabry Mohamed, M.D.
Reeba Annie Omman, M.D.

Last staff update: 6 December 2022 (update in progress)

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PubMed Search: Melanotic macule

Khaled Sabry Mohamed, M.D.
Reeba Annie Omman, M.D.
Page views in 2022: 2,127
Page views in 2023 to date: 600
Cite this page: Mohamed KS, Omman RA. Melanotic macule. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/skintumormelanocyticmelanoticmacule.html. Accessed January 29th, 2023.
Definition / general
  • Melanotic macule is a benign hyperpigmented lesion predominantly involving the mucosa or acral (volar) skin
  • Due to basilar hyperpigmentation of the mucosa or the epidermis
  • Typically no increase in the number of melanocytes (mild melanocytic hyperplasia occasionally)
  • No relation to sun exposure (except for ink spot lentigo) (Oral Surg Oral Med Oral Pathol 1976;42:196)
Essential features
  • Prominent basal layer melanin hyperpigmentation without an increase / minimal increase in the number of melanocytes
  • Sporadic or rarely associated with syndromes or diseases
Terminology
  • Mucosal melanotic macule; mucosal lentigo
  • Based on location:
    • Genital melanotic macule; vulvar melanosis; penile melanotic macule
    • Oral melanotic macule; melanotic macule of oral mucosa; labial melanotic macule
    • Volar melanotic macule (on the palms and soles)
    • Ungual melanotic macule (nails)
  • Based on etiology:
ICD coding
  • ICD-10:
    • L81.4 - other melanin hyperpigmentation
    • L81.8 - other specified disorders of pigmentation
Epidemiology
Sites
Pathophysiology
  • Unclear
  • Hypermelaninosis (increase in melanin pigmentation) without or occasionally slight increase in melanocyte number
  • May be due to increased melanocytic activity (Oral Dis 1999;5:80)
Etiology
Diagrams / tables

Images hosted on other servers:

Diseases and syndromic associations

Clinical features
Diagnosis
  • Clinical examination:
    • Genital melanosis: a thorough total body skin examination to rule out occult melanoma (J Am Acad Dermatol 2017;76:836)
    • Diffuse or multiple mucocutaneous pigmented macules: careful clinical examination and clinically relevant investigations to rule out associated syndromes
  • Dermoscopy:
  • Biopsy:
    • Oral melanotic macule: histological confirmation is necessary as any oral pigmented lesion is considered melanoma until proven otherwise
Laboratory
  • Laboratory tests typically not required; in patients with features suggestive of syndromic / systemic disease association, pertinent lab tests should be performed
Prognostic factors
  • Excellent with no malignant transformation
Case reports
Treatment
  • No treatment is required
Clinical images

Images hosted on other servers:

Labial melanotic macule

Congenital melanotic macules of the tongue

Labial melanotic macule in LHS

Dermoscopy in LHS

Microscopic (histologic) description
  • Increased basal keratinocyte pigmentation
  • Mostly restricted to tips of rete ridges
  • Dendrites are short and delicate
    • Coarse dendrites reaching to the upper epidermis are worrisome for early melanoma in situ
  • Melanin pigment incontinence and melanophages in the lamina propria or upper dermis
  • No increase in the melanocyte number (occasionally a very mild increase in melanocytes at the dermoepidermal junction may occur but typically have no atypia and lack confluence)
  • Associated frequent acanthosis, hyperkeratosis, hyperparakeratosis, spongiosis and elongated rete ridges (in nonoral lesions) (World J Clin Cases 2018;6:322)
Microscopic (histologic) images

Contributed by Khaled Sabry Mohamed, M.D.
Volar skin melanotic macule

Volar skin melanotic macule

Mucosal melanotic macule

Mucosal melanotic macule

Vulvar melanotic macule

Vulvar melanotic macule

Positive stains
Videos

Labial melanotic macule
(brown spot on lip)

Sample pathology report
  • Lip, biopsy:
    • Melanotic macule (see comment)
    • Comment: Sections show increased basilar pigmentation at the tips of rete ridges. Mild acanthosis and dermal melanophages are present. No significant increase in melanocytes is noted.
Differential diagnosis
  • Melanoma in situ:
    • Increase in irregularly scattered melanocytes restricted to the epidermis / mucosa
    • Confluence of melanocytes or presence of pagetoid spread
    • Melanocytes are atypical, epitheliod / spindled, pleomorphic, with eosinophilic or purple nucleoli (Massi: Histological Diagnosis of Nevi and Melanoma, 2nd Edition, 2014)
    • Coarse melanin granules may be seen
    • Heavy lymphoplasmacytic infiltrate
  • Melanoma:
    • Prominent atypical lentiginous melanocytes and often nested pattern of melanocytic hyperplasia with the atypical melanocytes invading the dermis
    • Dermal mitosis present
    • Pigment is not only restricted to basal layer but haphazardly distributed
  • Acquired mucosal nevus:
  • Lentiginous nevus:
    • Also known as jentigo
    • Rare melanocytic nests and melanocytic hyperplasia towards the edges
  • Lentigo simplex:
    • Increased melanocytes at the basal layer and epithelial hyperplasia
    • Pigmentation of the rete ridges
  • Solar lentigo:
    • Solar elastosis and bulb-like elongation of the rete ridges
    • Mild increase in melanocytes at the tips of rete ridges, giving dirty sock appearance
  • Ephelis:
    • No increase in melanocytes, diagnosis is usually clinical, appears during summer and fades in winter
    • Increased pigmentation (darkness of pigment increases with sun exposure)
  • Oral melanoacanthoma:
    • Pigmented, spongiosis and interspersed dendritic melanocytes (J Med Case Rep 2009;3:11)
    • Lack of melanocytic proliferation at the dermoepidermal junction but proliferation of dendritic melanocytes scattered throughout spinous layer present
  • Amalgam tattoo:
    • Due to dental silver fillings that may be implanted into the mucosa during dental procedure (PLoS One 2018;13:e0207026)
    • Dark brown to black or fine golden to dark brown granules deposited in the dermis
  • Smoker's melanosis:
    • Benign pigmentation of the oral mucosa, on anterior mandibular gingiva and interdental papillae
    • Adult onset and lesion continues to darken (J Periodontol 1991;62:524)
  • Racial pigmentation / physiologic pigmentation:
    • Macular pigmented areas of varying shapes and sizes
    • Shows increased melanin within the basal epithelial layer and melanin incontinence within the superficial lamina propria (Dermatol Ther 2010;23:220)
  • Drug induced pigmentation:
  • Postinflammatory hyperpigmentation:
    • Acquired excess of pigment in various conditions (infection, drugs, inflammatory diseases and others)
    • Epidermal postinflammatory hyperpigmentation: increased melanin pigment in the basal cell layer of the epidermis
    • Dermal postinflammatory hyperpigmentation: melanin pigment in the upper dermis, with pigment incontinence
Board review style question #1

A biopsy of the vulvar pigmented macule of a 42 year old patient shows basilar hyperpigmentation with no nest formation. SOX10 immunostain was performed and shows no increase in melanocytes. What is the best classification for this lesion?

  1. Invasive melanoma
  2. Melanoma in situ
  3. Melanotic macule
  4. Mucosal nevus
Board review style answer #1
C. Melanotic macule

Comment Here

Reference: Melanotic macule
Board review style question #2
Which of the following syndromes has associated melanotic macules?

  1. Brooke-Speigler syndrome
  2. Laugier-Hunziker syndrome
  3. Netherton syndrome
  4. Nevoid basal cell carcinoma syndrome
Board review style answer #2
B. Laugier-Hunziker syndrome

Comment Here

Reference: Melanotic macule
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