Post-inflammatory pigmentation

Pigmentation that occurs after acute or chronic inflammation of the skin is called post-inflammatory pigmentation.

1. Etiology and pathogenesis

Common causes of post-inflammatory pigmentation include:
(1) Some skin diseases such as eczema, lower limb stasis dermatitis, fixed drug eruption and papular urticaria, herpes zoster, dermatitis herpetiformis, impetigo, etc., can produce different degrees of pigmentation after recovery.
(2) Various physical and chemical factors, such as laser surgery, chemical peel surgery, skin grinding surgery, and friction, heat, radiation, drug stimulation, etc., can also cause pigmentation after local skin inflammation.
(3) Pigmentation can also occur after contact with asphalt, coal tar, cosmetics containing photosensitizers, etc., and after exposure to sunlight to cause photosensitive dermatitis.
The thiol groups in normal skin inhibit the oxidation of tyrosine to melanin, while some of the groups in the skin are removed during inflammation, which increases the activity of tyrosinase and causes local skin pigmentation. If inflammation occurs in the basal cells or at the junction of the epidermis and dermis, melanin is more likely to fall into the upper dermis and accumulate inside and outside the chromatophores, which can cause more persistent pigmentation.

2. Clinical manifestations

Pigmentation is generally limited to the site of skin inflammation, ranging from light brown, purple brown to dark black, scattered or flaky, with a smooth surface, sometimes accompanied by mild lichenification. For those with skin lesions on the exposed parts of the face that are exposed to sunlight or high temperature for a long time, the pigment spots may be reticular and have capillary dilation. Generally, there are no subjective symptoms.
Generally, pigmentation often occurs when inflammation occurs, and the pigmentation slowly fades after the inflammation disappears. It lasts for several weeks to several months, and some people continue for several years. The severity of skin pigmentation has little to do with the degree of inflammation, and mainly depends on the nature of the skin disease. Pigmentation is common and obvious in fixed drug eruptions, psoriasis, pyoderma, insect bite dermatitis, etc. Neurodermatitis, eczema, and lichen planus have lighter pigmentation or hypopigmentation after recovery. Pigmentation caused by discoid lupus erythematosus, fixed drugs, etc. is often persistent.

3. Diagnosis and differential diagnosis

This disease is easy to diagnose based on its characteristics of being more common in exposed areas, and pigmentation after dermatitis and surgery. This disease is mainly differentiated from tar melanosis. Tar melanosis is common in middle-aged women, and the incidence rate is higher in people who have long-term contact with coal tar, petroleum and its product processing. The pigmentation spots are fine reticular to patchy, light red at the beginning, and then turn to blue-gray to dark brown. They are often found in exposed areas such as the face, neck, and upper back, especially around the orbit and zygomatic and temporal areas, with no obvious boundaries from normal skin. Patients are often accompanied by systemic symptoms such as dizziness, fatigue, lack of appetite, and weight loss.

4. Treatment

This disease is often treated with topical hydroquinone cream, vitamin A acid cream, etc. Laser treatment is the same as melasma.

Source: Post-inflammatory pigmentation