aRTicle | dermatology | fibroblasts in the development of melasma4–6 . In fact,
the over-expression of both stem cell factors from fibroblasts and c-kit proteins have been found; the fibroblast-derived cytokines stimulate the proliferation and melanogenesis of melanocytes in culture4
. therefore,
it is possible that the dermal inflammation induced by the accumulation of UV irradiation may be associated with the activation of fibroblasts, which results in the up-regulation of stem cell factor (SCF) in melasma dermis, leading to increased melanogenesis 7
. recent data also revealed that melasma lesions have a
greater rate of vascularisation compared with the normal perilesional skin. Increased expression of vascular endothelial growth factors (VegF) in keratinocytes was suggested as the significant angiogenic factor for altered vessels in melasma8
. therefore, the network of cellular interactions between
keratinocytes, fibroblasts and perhaps vasculatures and melanocytes during chronic sun exposure may play an important role in the development of melasma. they may work in conjunction to stimulate melanocytes, resulting in epidermal hyperpigmentation7, 8
. Based on Wood’s lamp examination of the skin,
melasma can be classified into four main clinical types and patterns, with correlations in histology (in accordance with the depth of the melanin pigment)1, 2, 9, 10
:
■ epidermal. light brown, with an enhancement of pigmentation under Wood’s lamp; histologically, it is characterised by a melanin increase in the basal, suprabasal and stratum corneum layers ■ dermal. ashen or bluish–grey; no enhancement of pigmentation under Wood’s light; histologically, there Figure 1 The structure of the skin
is a preponderance of melanophages in the superficial and deep dermis ■ mixed. dark brown; enhancement of pigmentation under Wood’s lamp in some areas and not in others ■ Indeterminate. Inapparent under Wood’s lamp. the best therapeutical results are normally achieved in epidermal melasma11, 12
. melasma severity is scored using the melasma area
and Severity Index (maSI). In this system, the face is divided into four areas — forehead, right malar, left malar and chin — which correspond, respectively, to 30%, 30%, 30% and 10% of the total facial area. the melasma in each of these areas is graded according to three variables: the percentage of total area involved on a scale from 0 (no involvement) to 6 (90–100%; full involvement); darkness scoring from 0–4 is assessed according to a colour chart that the authors developed; and the scale of each patient is graded according to the comparison between the darkness of the melasma and the colour of the chart: ■ Scale 0: no melasma ■ Scale 1: light brown ■ Scale 2: brown ■ Scale 3: dark brown ■ Scale 4: black. the maSI is then calculated using the following
equation:
Mas i= 0.3(DF + HF)aF + 0.3(DMR + HMR) aMR + 0.3(DMl + HMl)aMl + 0.1(Dc + Hc)ac
Where d is darkness, H is homogeneity, a is area, F is the forehead, mr is the right malar, ml is the left malar, and C is the chin. the values 0.3, 0.3, 0.3 and 0.1 signify the respective percentages of total facial area. maSI was measured before treatment as a baseline and after each successive session10
. different therapeutic modalities have been used in the
treatment of melasma. Schematically, they can be distinguished in to: ■ topical and cosmetic treatments ■ Physical treatments ■ Chemical peeling ■ Injection treatments.
Topical and cosmetic treatments treatment with depigmenting agents should be continued for a number of months and are much more effective in the epidermal type of melasma.
Hydroquinone Hydroquinone is a hydroxyphenolic compound, which inhibits the conversion of doPa (3, 4-dihydroxy-phenylalanine) to melanin through the inhibition of tyrosinase13
. It has been the gold standard 18 ❚
for treatment of hyperpigmentation for a number of years. It is also believed to inhibit dNa (deoxyribonucleic acid) and rNa (ribonucleic acid) synthesis and to induce the degradation of melanosomes and destruction of melanocytes13, 14
. July 2011 |
prime-journal.com
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