Post-inflammatory Hyperpigmentation and Hypopigmentation (post-inflammatory hypermelanosis, post-inflammatory hypomelanosis)

Are You Confident of the Diagnosis?

What you should be alert for in the history

One should suspect postinflammatory hyperpigmentation (PIH) and hypopigmentation when a patient describes antecedent injury or inflammation of the affected area.

Characteristic findings on physical examination

Characteristic findings include hyper- and hypopigmented macules corresponding to areas of prior inflammation or injury, which may have an indistinct outline, in contrast to the discrete border seen in patients with vitiligo (depigmentation) or cafe au lait macules (hyperpigmentation). Epidermal hyperpigmentation manifests as light brown to black pigmentation, whereas dermal hypermelanosis confers a darker grey appearance to lesions. Figure 1 demonstrates post-inflammatory hyperpigmentation after acne on the back of a patient. Figure 2 is an image of post-inflammatory hypopigmentation from eczema on the arm of a child.

Figure 1.

Figure 2.

Expected results of diagnostic studies

Pigmentary changes may be more difficult to visualize in patients with lighter skin types. Wood’s (ultraviolet or black light) lamp allows one to differentiate between epidermal versus dermal hypermelanosis – areas of epidermal involvement will become more discrete under the lamp. Hypopigmented macules will appear more discrete under the Wood’s lamp. When noninvasive measures are equivocal, a biopsy may help to clarify the underlying etiology. In addition to standard hematoxylin-eosin staining, a Fontana-Masson silver stain for melanin can delineate the location of involvement (epidermis vs demis).

Diagnosis confirmation

Several skin conditions can mimic PIH. In the absence of an antecedent insult, the following disorders should be considered:

Medications: Carefully examine the patient’s medication list. Several medications, such as minocycline, can deposit in the dermis and appear to be PIH.

Acanthosis nigricans: will manifest as hyperpigmented, velvety plaques generally distributed to intertriginous regions.

Melasma: may present with tan to brown hyperpigmented macules (blue or black if there is dermal involvement) in malar, mandibular, or on the central face. Female patients with melasma may experience this progressive hyperpigmentation if they are on oral contraceptive pills or are pregnant. The key is that these patients will deny a history of trauma or inflammation to the area prior to the onset of hyperpigmentation.

Addison disease: may present with generalized cutaneous and mucous membrane hyperpigmentation that is worsened by sun-exposure. These patients will generally complain of malaise, weakness, anorexia, and weight loss.

Tinea versicolor: Patients may complain of hyperpigmented macules with fine scale in the winter months that become hypopigmented and more noticeable with sun exposure in the summer months. Scraping the area and performing a KOH examination under the microscope will provide evidence for presence of yeast filaments and spores.

Lichen amyloidosis/Macular amyloidosis: Both present with intense pruritus; however, lichen amyloidosis generally affects the lower extremities and is papular, whereas macular amyloidosis presents above the waist on the back and arms and is more patch-like.

Lichen planus: may also present with pruritus. Patients usually have hyperpigmented violaceous papules and plaques on flexor limbs and reticulated plaques on oral mucosa.

Poikiloderma of Civatte: presents as a symmetric, red-brown discoloration of bilateral lateral neck from chronic sun exposure. Notably, the anterior neck is spared.

Erythema dyschromicum perstans: is characterized by a progressive macular hyperpigmentation (ashy-grey) and can mimic lichen planus.

The differential for post-inflammatory hypopigmentation includes:

Vitiligo: Discrete macules are depigmented with well-circumscribed borders, unlike the hazy borders that often characterize post-inflammatory pigmentary changes.

Nevus depigmentosus: This congenital condition presents as hypopigmented macules or patches that do not progress in size or distribution after early childhood.

Idiopathic guttate hypomelanosis: Hypopigmented 2-5 mm macules may first appear on anterior legs and then progress to arms of middle-aged women and elderly patients.

Progressive macular hypomelanosis: Poorly circumscribed hypopigmented macules and patches have a distribution on the trunks of patients with Fitzpatrick skin types IV-VI. Generally there is no associated pain, itch, or antecedent inflammation.

Who is at Risk for Developing this Disease?

Post-inflammatory hyperpigmentation (PIH) and post-inflammatory hypopigmentation commonly occur in patients of all ages and genders but are more clinically obvious and longer lasting in patients with skin of color (Fitzpatrick skin types IV-VI). While the exact prevalence is unknown, PIH has been shown to be the third most common complaint for which African American patients see their dermatologist, after acne and atopic dermatitis, both of which can cause PIH.

What is the Cause of the Disease?

Etiology

Post-inflammatory hyperpigmentation (PIH) and hypopigmentation are responses of pigmented skin to a variety of exogenous and endogenous insults. It involves deposition of excessive pigment from activated melanocytes in the epidermis and/or dermis in response to inflammation or injury. UV exposure can cause PIH lesions to darken. Table I outlines skin disorders that can lead to post-inflammatory pigmentary changes. Table I. Causes of postinflammatory pigmentary changes