Histochemical and Immunohistochemical Study in Melasma: Evidence of Damage in the Basal Membrane

Abstract

The pathogenesis of melasma has not been clearly elucidated. Using Fontana Masson; diastase-resistant periodic acid-Schiff stains; and immunohistochemistry to stem cell factor (SCF), its receptor c-kit, anti-mast cell tryptase, and anti-collagen type IV antibody, we evaluated melasma lesions and compared them with perilesional skin and photoprotected skin. Samples were taken from lesional and photoprotected nonlesional skin in 24 patients. In other 24 patients, we took biopsies of lesional and perilesional skin. With Fontana Masson, we observed many pigmented basal cells protruding into the dermis of the melasma skin. Periodic acid-Schiff stain and anti-collagen type IV showed damage on the basal membrane in 95.5% and 83%, respectively, in melasma lesion. The immunoreactivity of SCF and the prevalence of mast cells were increased in the dermis of melasma compared with perilesional dermis. The expression of c-kit was significantly increased at lesional epidermis; a frequent protrusion of c-kit-positive basal cells into the dermis was evident in 70% versus that in 29% of perilesional skin. The expression of c-kit was increased at lesional dermis of melasma compared with perilesional skin. We found a low correlation between c-kit expression and prevalence of mast cells; these were increased in melasma skin. The results may suggest a role of SCF, c-kit, and mast cells in the pathogenesis of melasma. We were surprised by the unexpected evidence of damage to basal membrane (BM), which could facilitate the fall or the migration of active melanocytes and melanin into the dermis allowing the constant hyperpigmentation in melasma.

Clues to the Pathogenesis of Melasma from its Histologic Findings

“…Since free melanin and melanophages are present in the dermis of melasma skin, disruption of the basement membrane could facilitate the descent or the migration of melanocytes and melanin into the dermis [7,9]. Histologic findings such as the protrusion of pigmented basal cells into the dermis of 66% of melasma skin samples compared with that of pigmented basal cells into the dermis of 20% of photoprotected nonlesional skin samples, support this hypothesis [9].…”

“…The median prevalence of dermal mast cells was significantly higher in melasma skin than in perilesional normal skin (173 ± 57% vs. 145 ± 57%, p=0.04) [8]. Using an antitryptase antibody, the number of mast cells detected was 58 ± 39.9 cells/mm 2 in melasma skin compared with 37 ± 28.8 cells/mm 2 in perilesional normal skin (p<0.04) [9].…”

“…However, the same author recently reported that pendulous melanocytes associated with basement membrane abnormalities are a characteristic feature of melasma [14]. Another study of melasma patients with Fitzpatrick skin types IV and V revealed that D-PAS staining and anti-collagen type IV immunohistochemistry indicated damage to the basement membrane in 95.5% and 83% of the skin samples, respectively [9]. Basement membrane disruption could be caused by elevated levels of matrix metalloproteinase (MMP)-2 and MMP-9, which degrade type IV collagen and type VI collagen in the skin during chronic UV exposure [15].…”

“…Fontana-Masson staining has shown that, the melanin content of melasma skin is higher in all layers of the epidermis, including the stratum corneum, than that in perilesional normal skin [7][8][9]. Image analysis of Fontana-Massonstained sections of skin from 22 patients with melasma showed a significant difference in the density of melanin between melasma skin (mean ± standard deviation [SD]: 0.37 ± 0.02) and perilesional normal skin (0.34 ± 0.02) (p<0.01) [10].…”

Melasma, Novel Treatment Modalities

“…Histopathologically, melasma is associated with epidermal hyperpigmentation due to increased melanin formation and deposition rather than increased melanocyte numbers, weak basement membrane, elastosis, vascular proliferation with mild lymphohistiocytic infiltrates increased numbers of mast cells and dermal melanophages [2,3].…”