Post-inflammatory Hyperpigmentation of Skin

Hyperpigmentation occurs as brown macules or patches often with a poorly defined border, irregular in outline, and usually with little surface change.¹ The basic mechanism in response to various triggers (see Causes, below) is melanosis of the epidermal or dermal layer of the skin. Arachodonic acid in the epidermal layer is oxidised to leukotrienes, prostaglandins and other products that stimulates melanocytes to increase the production of melanin. In dermal melanosis, inflammation disrupts the basal layer, causing melanin to be released and trapped in the macrophages of the papillary dermis, a process with the delightful name of pigmentary incontinence.²

Pigmentary changes are much more common in darker skinned individuals of Asian or African origin and pigmentation follows many common inflammatory diseases such as eczema, psoriasis or acne. Where erythema is seen in white individuals, pigmentation occurs in dark skinned individuals.

Pigmentation due to increased melanin is a dirty brown colour, as opposed to that due to haemosiderin pigmentation following purpura which is more a rusty brown colour.³ Hyperpigmentation on the face may be due to pregnancy or taking the contraceptive pill (melasma/chloasma).⁴
Other conditions which may enter into the differential diagnosis include:²

• Acanthosis nigricans
• Addison's Disease
• Amyloidosis - lichen or macular
• Tinea versicolor.

• Inflammatory skin conditions Any inflammatory skin condition involving the dermo-epidermal junction can cause hyperpigmentation, e.g. eczema, psoriasis, lichen planus, acne, systemic lupus erythematosus, chronic dermatitis, and cutaneous T-cell lymphoma.
• Trauma
• Allergic Reactions
• Photoxocicity
• Drugs Chlorpromazine, chloroquine and arsenic, are all common culprits. Other drugs which occasionally cause hyperpigmentation include tetracycline, bleomycin, doxorubicin, 5-fluorouracil, busulfan, antimalarial drugs and hormones (e.g. oestrogen).
• Exposure to ultraviolet light
• Exposure to chemicals such as silver, gold, and arsenic
• Idiopathic Occasionally no cause can be identified.

• Wood's light may help to differentiate dermal from epidermal hyperpigmentation which may help to elucidate the cause.
• Biopsy may be required, especially if there is no identifiable preceding inflammation to account for the pigmentation.

• The condition may resolve in time without additional treatment.
• Avoidance of sun exposure may prevent further hyperpigmentation occuring on the face. Daily use of a high factor sunscreen may be helpful.
• The underlying cause should be treated if possible.
• If treatment is required, skin lightening creams may help. Hydroquinine 2% is usually prescribed first line but may not be very effective. ²
• A retinoid such as tretinoin may be helpful, particularly in sun-damaged skin.⁵
• A topical steroid may help if there is an underlying inflammatory process but caution should be used in applying steroid creams to the face due to skin thinning. Recently a triple therapy has been tried using a combination of steroid, retinoid and 4% hydroquinone.⁶
• Other treatments being developed which have shown some depigmenting activity include a combination of retinaldehyde (a retinoic acid precursor) and glycolic acid⁷, and the peroxidase inhibitor methimazole, which inhibits the production of melanin.⁸

Patients should be warned that the pigmentation may be slow to resolve, even with treatment. Epidermal pigmentation may persist for 6-12 months. Dermal pigmentation may persist for years.

If the diagnosis is in doubt or the patient requests specialist advice, referral should be considered.