Postinflammatory hyperpigmentation (PIH), also called acquired melanosis, is an acquired transient pigmentation following inflammatory conditions, skin damage, or therapeutic interventions. Darker skin types seem to experience it the most. PIH occurs with equal incidence in males and females of all ages.
Dermal melanosis occurs when inflammation disrupts the basal cell layer, causing melanin pigment to be released and subsequently trapped by macrophages in the papillary dermis. On the other hand, arachidonic acid is released during the epidermal inflammatory response, where it is oxidized to produce prostaglandins, leukotrienes, and other substances. These inflammatory byproducts affect melanocyte and immune cell function. These inflammatory substances specifically activate epidermal melanocytes, leading them to enhance melanin synthesis and subsequently increase pigment transfer to neighboring keratinocytes.
When PIH causes inflammation in the epidermis, melanocytes are stimulated to produce more melanin and transfer it to nearby keratinocytes. Acne excoriée, lichen planus, systemic lupus erythematosus, chronic dermatitis, and cutaneous T-cell lymphoma, particularly erythrodermic variations, are examples of common inflammatory illnesses that lead to PIH. A few drugs may also contribute to PIH. These include tetracycline, chemotherapeutic treatments like bleomycin, 5-fluorouracil, and busulfan, as well as antimalarial medications.
PIH presents at the original insult site after it has healed. The lesions’ coloring ranges from pale brown to black. If the patches are exposed to sunlight, they could get darker.
The diagnosis of PIH is typically made clinically; no particular testing is necessary. Dermal PIH and epidermal PIH can be distinguished using a Wood lamp examination. To rule out additional underlying causes of hyperpigmentation, a skin biopsy is necessary. Melanin can be localized in the epidermis and/or dermis by staining the biopsy samples with Fontana-Masson silver stain.
Treatment for PIH is frequently a challenging and lengthy process that frequently takes 6 to 12 months to produce the necessary depigmentation. Topical treatment for PIH aims to bleach the lesion and includes hydroquinone, azelaic acid, vitamin C cream, tretinoin, corticosteroids, glycolic acid, kojic acid, arbutin, and licorice extracts. Physical treatment for PIH includes chemical peels, laser treatments, and intense pulsed light therapies. If pigmentation affects an exposed site, daily application of broad-spectrum SPF sunscreen is important.
Without therapy, the clinical symptoms of epidermal melanosis could take months or even years to go away. People with dark complexion may experience PIH for a longer period of time than people with light skin. UV exposure and ongoing or recurrent inflammation can exacerbate the condition.
Mohammed Alahmadi, medical Student
Maee Barakeh, medical student