Chloasma (Melasma)

Synonyms: Melasma, Mask of pregnancy, Chloasma medicamentosum

Chloasma comes from the Greek chloazein, to be green. It is considered to be something of a misnomer and many dermatologist prefer the term melasma (melas is Greek for black). The pathophysiology is largely unknown but many differences have been noted between chloasma and normal skin. There is, for example, an increase in the level of melanin, large numbers of melanocytes and melanosomes and increased synthesis of tyrosinase.¹ One study also found an increased level of solar elastosis (increase in elastin tissue resulting from sun exposure) and propounded that chloasma was a result of a cumulative sun exposure, in a microenvironment of cutaneous photoageing in which inflammatory cells, particularly mast cells, play a key role.² Another found an increase in oestrogen receptor expression, suggesting a hormonal link.³

The exact incidence of chloasma is unknown, but it is a common condition.There is a female to male predilection, with a ratio of 9:1.⁴

Risk factors

These include:

• Dark skin - it is common in Asians and Hispanics.⁴
• Hormonal - chloasma occurs commonly in pregnancy. One study in Iran found a prevalence among 400 pregnant patients of 15.8%.⁵ It is rare before puberty and is commonest in women during their reproductive years.⁴ It is linked to use of oral contraceptives.⁶ One study of patients with chloasma found that the frequency of thyroid disorders was four times greater compared to a control group.⁷
• Sun exposure - this is a well established risk factor.⁶ Chloasma occurs in sun-exposed areas of the skin.⁴
• Genetics - 30% of patients report a positive family history and identical twins with chloasma have been reported.⁴
• AIDS - one study reported a group of AIDS patients who developed chloasma-like hyperpigmentation of the face.
• Other pigmented lesions - one study found a higher incidence of chloasma in women who also had lentigines or melanocytic naevi.⁸

Patients usually complain of gradual onset areas of dark skin. The colour may vary from tan to brown, but may be black or have a bluish tinge. The distribution is usually symmetrical. Three patterns are commonly seen - centrofacial, malar or mandibular.

• Addison's disease
• Drug-Induced photosensitivity
• Discoid lupus erythematosus
• Mastocytosis (mast cell proliferation and accumulation within various organs, most commonly the skin)
• Poikiloderma of Civatte (erythema associated with a mottled pigmentation seen on the sides of the neck, more commonly in women)

Wood's light helps to locate the pigmentation in the dermis or epidermis. In many cases, it is found in both locations.⁴

• Chloasma is a difficult condition to manage, as sunlight is a considerable aggravating factor and it is difficult to prevent exposure even with high factor protection creams.
• Mild cases may simply require reassurance. Chloasma associated with pregnancy should resolve spontaneously within a few months. A variety of therapies are available but if treatment in primary care is unsuccessful after six months, specialist referral should be considered.
• Lightening agents seem to be the best treatment. Hydroquinone 4% has been the commonest used⁹ but its availability is restricted in some parts of the world due to concerns about its long-term effects (mainly exogenous ochronosis, an irregular blue-black staining affecting sun-exposed skin and nails).¹⁰ It is however still currently available in the UK. Other lightening agents that have been tried include tretinoic acid, ascorbic acid and azelaic acid either alone or in combination.
• Tretinoic acid used as monotherapy can be effective but improvement is slow. It is thought to act by inhibiting the function of melanosomes.
• Triple therapy cream containing hydroquinone, tretinoin and fluocinolone acetonide has been found in one study to be more cost-effective than hydroquinone alone.¹¹
• Other agents that have been tried include 4-N -butylresorcinol, phenolic-thioether, 4-isopropylcatechol and kojic acid. One study reports that pidobenzone 4% lipogel used twice a day for sixteen weeks is safe and effective.¹² Azelaic acid can be as effective as 4% hydroquinone and is more effective than 2%. The mechanism of action is not well understood.
• Sometimes a peeling agent such as glycolic acid is added.¹³
• Laser treatment, intense pulse light therapy and medium-depth chemical peels are also sometimes employed to hasten resolution. Some authorities believe these destructive 'quick fix' therapies to be unpredictable and associated with an increase incidence of adverse events (e.g. epidermal necrosis, postinflammatory hyperpigmentation and hypertrophic scarring).⁹ Recent developments in technology have resulted in lasers which are more effective and safer; they have been used successfully in patients resistant to other forms of treatment.^14,15 Light microscopy studies show a general reduction in melanocyte content in after a certain type of laser treatment (fractional photothermolysis).¹⁶ Moreover, the use of intravenous vitamin C to reduce hyperpigmentation after laser treatment has been reported.¹⁷

Most cases resolve eventually, but can take a long time to do so. Continued exposure to sunlight tends to hamper treatment and lead to recurrence. Resolution will also take longer in patients with extensive dermal melanin compared to those in whom pigmentation is mainly in the epidermal layer.⁴