Postinflammatory Hyperpigmentation

Etiology

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. Other etiologies include[1][4]:

Infections

• Viral exanthems
• Fungal infections
• Impetigo

Allergic/Immunologic

• Contact dermatitis
• Atopic dermatitis
• Scleroderma
• Sarcoidosis
• Systemic lupus erythematosus
• Dermatomyositis
• Insect bite reaction

Papulosquamous Disorders

• Psoriasis
• Lichen planus
• Pityriasis rosea
• Lichen simplex chronicus

Cutaneous Injury

• Laser/light therapy
• Burns
• Cryotherapy
• Chemical peels
• Radiation therapy

Medication Hypersensitivity Reactions

Miscellaneous

• Acne vulgaris
• Mycosis fungoides
• Erythema dyschromicum perstans

Epidemiology

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%.[4][5]

Pathophysiology

Postinflammatory hyperpigmentation, or hypermelanosis, results from the 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.[1][6]

Histopathology

If a biopsy is performed, epidermal PIH histopathology is significant for increased melanin in keratinocytes. The presence of melanin in dermal macrophages is noted in dermal melanosis. A biopsy may also be useful in determining the etiology of the underlying inflammation.[7][8]

History and Physical

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 initial inflammation or injury distribution. Epidermal hyperpigmentation is tan, brown, or dark brown 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.[1][7]

Evaluation

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 the diagnosis is uncertain or if the underlying etiology has yet to be determined. Laboratory evaluation to rule out Addison's disease and systemic lupus erythematosus may be necessary if signs and symptoms are present.[4]

Treatment / Management

Treatment of PIH is typically stepwise and includes multiple modalities in addition to daily protection against ultraviolet radiation. The first step is treating 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 hypomelanosis 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 can be used 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. Still, it 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 effectively treat underlying acne and PIH and may be used long-term. Azelaic acid can also treat both acne and PIH.

Chemical Peels

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. 

Laser Therapy

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, experienced clinicians should also use them cautiously, as they can cause skin irritation and additional hyperpigmentation.[4][9]

Differential Diagnosis

The differential diagnosis of postinflammatory hyperpigmentation includes:

• Melasma
• Solar lentigines
• Tinea versicolor
• Acanthosis nigricans
• Lichen planus pigmentosus
• Macular amyloidosis
• Ochronosis (patchy hyperpigmentation)
• Erythema dyschromicum perstans morphea
• Discoid lupus erythematosis[7]

Prognosis

Epidermal hyperpigmentation typically resolves or significantly improves within 6 to 12 months, whereas dermal hyperpigmentation improves slowly and may be permanent. No morbidity beyond psychological distress is associated with it, although recurrences are common, especially if photoprotection is not employed.[6]

Complications

Complications of untreated PIH include worsening hyperpigmentation and psychological distress. Complications of treatment include skin irritation and post-procedure hyperpigmentation.[6][10]