A 7-year-old African American girl was brought to her pediatrician by her mom who was worried that she was itching and that her skin was getting darker. The pediatrician knew the girl well as a patient with asthma and allergic rhinitis. In fact, the girl performed the allergic salute more than once in the office as she rubbed her itchy nose. Morgan-Dennie lines were seen under her eyes (Figure 168-1A). The mom undressed the girl to show the dark patches of skin around her knees (Figure 168-1B). Atopic dermatitis is common in the popliteal fossae and this girl clearly demonstrated the atopic triad: atopic dermatitis, asthma, and allergic rhinitis. The darkening of the skin around the knees and also seen on the neck is related to the scratching and rubbing of the skin secondary to the pruritus of atopic dermatitis. The pediatrician explained to the mom and child about the need to more aggressively treat the atopic dermatitis with emollients and topical steroids. No promises were made about the reversibility of the hyperpigmentation as each patient will respond differently to treatment.

Postinflammatory hyperpigmentation (PIH) is an accumulation of melanin in response to chronic inflammation that usually appears as brown, black, or grey macules or patches in the pattern of an underlying inflammatory condition. Postinflammatory hyperpigmentation can result from any kind of irritant to the skin, but is more common in conditions resulting in chronic irritation and inflammation, and is more common in individuals with darker Fitzpatrick Skin Types IV, V, and VI. It is more severe and longer lasting if the underlying inflammatory condition goes untreated though most PIH will fade within 6 to 12 months of treating the underlying inflammatory condition. For the girl in the preceding case, the PIH may resolve without treatment after her atopic dermatitis clears up, but if the atopic dermatitis persists then the PIH will continue until the resolution of the underlying condition.

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  The prevalence of disorders of hyperpigmentation including post-inflammatory hyperpigmentation in the general population ranges from 0.42 percent in Kuwait to 55.9 percent in a sample population from Michigan.¹

  
  
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  The prevalence in children in the US is around 22 percent based on a sample of hospitalized children in Kentucky.²

  
  
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  Postinflammatory hyperpigmentation (PIH) is one of the most common types of cutaneous hyperpigmentation, and although there are no good estimates of its prevalence in the children of the US, studies in Nigeria estimate PIH to represent 49.5 percent of skin lesions present in hospitalized children.³ In studies of adults, “dyschromia” is often used to combine disorders of hyperpigmentation, which would include melasma, lentigines, and PIH so true prevalence is difficult to obtain. In one study dyschromia was the second most common diagnosis among African American patients, but failed to make it into the top 10 for Caucasian patients.⁴

  
  
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  The distribution of PIH is equal among males and females of all ages.⁵

  
  
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  PIH is more common in dark-skinned individuals (Fitzpatrick skin types IV, V, and VI), and therefore is frequently found in individuals from Asia, Africa (Figure 168-2), South America, and Native Americans.⁶

  
  
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  The age at which a child could present with a hyperpigmented lesion varies, and PIH, erythema ab igne, and confluent and reticulated papillomatosis (CARP) are more common in older children and young adults versus young children (Figure 168-3).⁷

  
  
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  Other hyperpigmented lesions such as “linear and whorled hypermelanosis,” nevus of Ota, and Café au Lait spots are linked to embryologic mosaicism or genetic abnormalities, and may be seen at birth or within a few weeks after birth (Figures 168-4 and 168-5). Mongolian spots are nearly always present at birth (Figure 168-6).⁷

  
  
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  Just as PIH is most common in darker-skinned individuals, Nevus of Ota, Mongolian spot, Café au Lait macules, and CARP are more common in Asians and Blacks.⁷ Conversely, linear and whorled hypermelanosis shows no racial predilection.⁸

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  The most common causes of postinflammatory hyperpigmentation are acne vulgaris, atopic dermatitis (Figure 168-7), and impetigo, but any insult to the skin from bug bites and minor burns to drug reactions and other rashes can result in postinflammatory hyperpigmentation.^1,5

  
  
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  Postinflammatory hyperpigmentation may be divided based on whether the pigment accumulates in the epidermis or in the dermis. This can be helpful in terms of understanding the pathophysiology, characteristic appearances, and treatment modalities associated with the two categories.

  
  
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  Epidermal hyperpigmentation is thought to be in part caused by the release of inflammatory molecules such as prostanoids, cytokines, chemokines, and other products of arachidonic acid which leads to increased melanocyte activity, increased melanin production and release, and accumulation of melanin in adjacent keratinocytes.^1,5,9,10

  
  
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  Dermal hyperpigmentation is thought to result from inflammatory mediated destruction of keratinocytes, which results in melanin release and its accumulation within macrophages in the upper dermis.¹ Histologically this is described as “pigment incontinence.”

  
  
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  The distinction between accumulation of pigment in the epidermis and accumulation of pigment in the dermis is reflected in the appearance of the lesion on the skin. Dermal lesions tend to be a blue-gray color with indistinct boundaries and epidermal lesions tend to be tan, brown, or dark brown and with more sharply demarcated borders.^1,11

  
  
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  In other disorders of hyperpigmentation the connection between the pathophysiology and the cutaneous appearance also exists; the color and shape of the pigment generally reflects both the location of melanin and the degree of melanocytic hyperplasia or release of melanin.⁷

Clinical Features

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  The degree of pigmentation is strongly correlated with the total duration of the inflammatory process, where chronic or relapsing inflammatory processes cause darker and longer lasting hyperpigmentation.¹

  
  
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  Darker-skinned individuals have larger and more densely distributed melanin pigment in their skin. In turn, they tend to react to inflammation with more accumulation of pigment, and therefore PIH tends to present with darker lesions that last longer.^1,12

  
  
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  UV exposure is also associated with darkening and persistence of hyperpigmented lesions.¹³

  
  
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  The location of the pigmentation in the skin also effects the persistence of PIH, and dermal hyperpigmentation tends to last longer since the dermis does not continuously turnover like the epidermis.¹³

Typical Distribution

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  Postinflammatory hyperpigmentation typically follows the pattern of the initial inflammatory process and consists of macules or patches.¹²

Laboratory and Imaging

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  A Wood’s lamp examination can be used to distinguish between epidermal and dermal hyperpigmentation, where epidermal lesions will have distinct margins and a prominent border whereas dermal lesions will have fluffy, indistinct margins.⁵

Biopsy

In general, skin biopsies are unnecessary, but if the etiology is uncertain a 4-mm punch biopsy can help determine the underlying cause of PIH. The Fontana-Masson stain is used to identify melanin in the skin and is useful in distinguishing between epidermal and dermal hyperpigmentation.⁵

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  CARP is characterized by hyperkeratotic or verrucous scaly brown papules that coalesce into plaques, with peripheral reticular pattern with or without pruritus (Figure 168-8). It is generally first seen in inframammary region or interscapular region, and often spreads to the chest or abdomen (Figure 168-3). It can be found on the face, neck, extremities, flanks, or gluteal cleft. The etiology is unknown, but potential causes include a keratinization disorder, a reaction to a fungal or bacterial infection, photosensitivity, amyloidosis, and genetic factors.^14,15