Ann Dermatol.  2020 Apr;32(2):101-108. 10.5021/ad.2020.32.2.101.

Exploratory Study of Epidermis, Basement Membrane Zone, Upper Dermis Alterations and Wnt Pathway Activation in Melasma Compared to Adjacent and Retroauricular Skin

• Espósito
• Brianezi G
• de Souza N
• Miot LD
• Miot HA

• KMID: 2471335
• DOI: http://doi.org/10.5021/ad.2020.32.2.101

Abstract

BACKGROUND
Melasma is a chronic acquired focal hypermelanosis which pathogenesis has not been fully elucidated. Classical pathophysiologic studies have analysed the affected and perilesional areas, but little is known about the status of sun-protected skin, which is subjected to the same endogenous and genetic factors.
OBJECTIVE
To assess the histological characteristics of melasma compared to adjacent and retroauricular skin.
METHODS
Skin samples were collected from 10 female from: melasma, perilesional area and retroauricular. The samples were stained (haematoxylin-eosin, periodic acid-Schiff, Fontana-Masson, picrosirius red, toluidine blue and Verhoeff), immunolabelled for CD34 and Wnt1. The data from the skin sites were analysed simultaneously by a multivariate model.
RESULTS
Melasma skin exhibited noteworthy stratum corneum compaction, greater collagen heterogeneity, solar elastosis, higher number of mast cells, basement membrane zone (BMZ) damage, Wnt1 expression, pendulum melanocytes, higher cellularity and vascular proliferation at the superficial dermis. Stratum corneum compaction, collagen heterogeneity and BMZ abnormalities were variables associated to melasma that not follow a continuum through retroauricular to adjacent skin. Mast cell count was the variable that disclosed correlation with the most other abnormalities as well as had the greater contribution in the multivariate model.
CONCLUSION
In addition to melanocyte hyperactivity, melasma skin exhibits alterations in the epidermal barrier, upper dermis and BMZ, which differ from the adjacent sun-exposed skin and retroauricular skin, indicating a distinct phenotype, rather than a mere extension of photoageing or intrinsic ageing. Mast cells appear to play a central role in the physiopathology of melasma.

Keyword

Basement membrane; Dermis; Epidermis; Melanosis

MeSH Terms

Basement Membrane*
Collagen
Dermis*
Epidermis*
Female
Humans
Hyperpigmentation
Mast Cells
Melanocytes
Melanosis*
Phenotype
Population Characteristics
Skin*
Tolonium Chloride
Wnt Signaling Pathway*
Collagen
Tolonium Chloride

Figure

• 

  Fig. 1 Haematoxylin-eosin staining shows thinning of the stratum corneum in melasma (A) and adjacent (B) skin and greater compaction in the melasma sample. Solar elastosis exhibited increased progressively expression across the investigated skin types and it was greater in melasma (A) than in the adjacent skin (B) and retroauricular (C) skin. Fontana-Masson staining shows the progressive increasing in the epidermal melanin pigmentation across the skin types, which was greater in melasma (D) than in the adjacent skin (E) and retroauricular (F) skin. The melanin density in the dermis did not differ between samples. (A~C) ×100, (D~E) ×200.

• 

  Fig. 2 Melasma (A), adjacent (B) and retroauricular (C) skin subjected to Verhoeff staining: the elastotic material is more prominent in the most sun-exposed skin, specifically melasma (A). Picrosirius red staining showed greater collagen heterogeneity in the papillary dermis of melasma (D) than in the adjacent (E) and retroauricular (F) skin. (A~E) ×200.

• 

  Fig. 3 Melasma (A), adjacent (B) and retroauricular (C) skin subjected to periodic acid-Schiff staining: basement membrane changes was more prominent in melasma skin (A). CD34 immunohistochemical showed larger number of blood vessels more evident in melasma (D) than in the adjacent (E) and retroauricular (F) skin. The white arrows are pointing to the pendulum melanocytes while the black arrows are pointing the basement membrane disruptions. (A~C) ×100, (D~E) ×200.

• 

  Fig. 4 Mast cells in the superficial dermis (arrows) of melasma skin, with preferential perivascular topography and metachromatic granules (purple), as assessed using toluidine blue staining (×100).

• 

  Fig. 5 Melasma (A), adjacent healthy skin (B) and retroauricular skin (C) with double-labelling double immunofluorescence for Wnt1 (red/cytoplasmic). The blue colour is related to the nucleus marker (4′,6-diamidino-2-phenylindole).

• 

  Fig. 6 Perceptual map from multiple correspondence analysis of the investigated histological variables for melasma, adjacent skin and retroauricular skin. Thirteen variables were included allowing to explain 65% of the variance of the two-component model. Solar elastosis, collagen heterogeneity, dermal cellularity, mast cell number, presence of pendulum melanocytes, presence of vascular structures, abnormalities of the elastic fibres and Wnt1 expression shown the strongest correlation with the facial skin locations because they present similar quadrangular distribution.

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