Postinflammatory hyperpigmentation (PIH) is a common acquired cutaneous disorder occurring after skin inflammation or injury. It is chronic and is more common and severe in darker-skinned individuals (Fitzpatrick skin types III–VI). While the condition typically improves spontaneously, this process can take months to years, necessitating prolonged treatment. Combination therapy is the most effective.
While any inflammatory skin condition can result in hyperpigmentation, the most common causes of PIH in patients with darker skin color are acne vulgaris, atopic dermatitis, and impetigo.
Medication Hypersensitivity Reactions
PIH can occur at any age in all skin types but is more common in Fitzpatrick skin types III-VI. The darker the skin color, the more intense and persistent hypermelanosis tends to be. There is no gender difference. The incidence of PIH in darker-skinned patients with acne can be as high as 65%.
Postinflammatory hyperpigmentation, or hypermelanosis, results from overproduction of melanin or abnormal melanin deposition in the epidermis or dermis following inflammation. Inflammatory mediators trigger melanocyte hypertrophy and activity, which increases melanin production in the epidermis. In deeper processes extending to the dermis, basal keratinocytes are damaged and release large amounts of melanin. The melanin is phagocytosed and deposited, causing a blue-gray discoloration of the skin, which may be permanent. Hyperpigmentation limited to the epidermis has a higher likelihood of resolution than dermal hyperpigmentation.
Patients with PIH have a history of an inflammatory disorder of the skin or skin injury in the same distribution. Once the underlying inflammation has resolved, PIH is asymptomatic. However, psychological distress and impact on the quality of life may persist.
On physical examination, PIH appears as irregular, hyperpigmented macules or patches in the distribution of the initial inflammation or injury. Epidermal hyperpigmentation is tan, brown, or dark brown in color and may persist for months to years without treatment but does tend to improve over time as the underlying inflammatory disorder resolves. Wood’s lamp examination of epidermal PIH may reveal fluorescence. Dermal hyperpigmentation is blue-gray and may be permanent. Dermal and epidermal hyperpigmentation may both be present. If the inflammatory process is still active, erythematous papules, plaques, or nodules may also be visible.
The diagnosis of PIH is clinical. Wood’s lamp evaluation can help distinguish between epidermal and dermal PIH. A biopsy may be useful for confirming the diagnosis if uncertain or if the underlying etiology has yet to be determined. Laboratory evaluation to rule out Addison disease and systemic lupus erythematosus may be necessary if signs and symptoms are present.
Treatment of PIH is typically stepwise and includes multiple modalities in addition to daily protection against ultraviolet (UV) radiation. The first step is the treatment of the causative inflammatory disorder if it is still active. Topical lightening therapy, often in combination, is next, followed by chemical peels and/or laser therapy for severe or refractory cases. Treatment lasting months to years is often required; patient education should set the expectation that improvement of hypermelanosis is slow and recurrences are common.
Topical Therapy - tyrosinase inhibitors (prevent melanin production)
The mainstay of treatment is a topical lightening agent such as hydroquinone (mequinol if a less irritating agent is needed). It is often combined with a topical retinoid with or without a topical steroid to enhance and speed effectiveness. A commonly used triple combination includes hydroquinone 4%, tretinoin 0.05%, and fluocinolone acetonide 0.01%. The topical steroid can lessen the irritant effects of the skin lightener and/or the retinoid but should only be used for up to 8 weeks to minimize the likelihood of steroid-induced skin changes. Topical retinoids include tretinoin, adapalene, and tazarotene. They are effective at treating underlying acne as well as PIH and may be used long term. Azelaic acid can also treat both acne and PIH.
Chemical peels work by removing the epidermal cells containing excess melanin. They must be used with caution by experienced clinicians as they can cause skin irritation and additional hyperpigmentation. Glycolic, salicylic, and trichloroacetic acid peels are common.
Multiple laser types, including Q-switched ruby lasers, Q-switched Nd:YAG lasers, and picosecond (short, intense pulse) lasers have been used to treat PIH as has fractional photothermolysis. However, they also should be used with caution by experienced clinicians as they can cause skin irritation and additional hyperpigmentation.
The differential diagnosis of postinflammatory hyperpigmentation includes:
Epidermal hyperpigmentation typically resolves or significantly improves within 6 to 12 months, whereas dermal hyperpigmentation improves more slowly and may be permanent. No morbidity beyond psychological distress is associated with it, although recurrences are common, especially if photoprotection is not employed.
Dermatologic consultation may be helpful in refractory cases or if chemical peels or laser therapy are therapeutic considerations.
Broad-spectrum, year-round UV protection with sunscreen and protective clothing should be initiated at diagnosis and throughout treatment regardless of skin color. Patients with darker skin types may be less likely to use sun protection without education due to a lack of perceived importance.
Combination therapy is more effective than monotherapy.
Aggressive treatment is more likely to lead to skin irritation and further hyperpigmentation; patience is necessary.
Patients should use broad-spectrum photoprotection daily.
All members of the healthcare team should work in conjunction to prevent and treat PIH by educating patients on the use of broad-spectrum sunscreen and protective clothing when sun avoidance is not possible. Education on the usually self-limiting nature of PIH is also helpful. Primary care providers may initiate treatment with topical agents and may choose to refer to dermatology for chemical peels or laser therapy.
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