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Postinflammatory hypopigmentation
Postinflammatory hypopigmentation
Clinical features Postinflammatory hypopigmentation is relatively common and is often a cosmetic nuisance in patients with darker skin.1,2 Almost any inflammatory dermatosis may result in areas of hypopigmentation and these are not infrequently combined with areas of hyperpigmentation. Hypopigmentation in eczema, psoriasis, blistering disorders, lichen sclerosus, scleroderma, morphea, and pityriasis lichenoides is not rare, and some diseases (including infections) characteristically present with hypopigmentation. These include pityriasis versicolor, indeterminate and tuberculoid leprosy, post-Kala-azar dermal leishmaniasis, pinta, and pityriasis alba.1โ4 Loss of pigment may also occur in sarcoidosis, syphilis, and graft-versus-host disease.2,5 Interface dermatoses (i.e., lupus erythematosus lichen planus) are more often associated with hyperpigmentation. Postinflammatory hypopigmentation is also seen after cryotherapy and dermabrasion and less commonly associated with the use of various lasers.5
Histologically, the changes are often subtle and consist of mild hyperkeratosis, focal parakeratosis, minimal spongiosis, and variable exocytosis of lymphocytes.16 This is associated with mild loss of melanin in basal keratinocytes but not in the number of melanocytes.6 In the dermis there is mild pigment incontinence and a sparse superficial, perivascular lymphohistiocytic inflammatory cell infiltrate. A histologic study of pityriasis alba in non-atopic patients found predominantly follicular pathology with infundibular spongiosis, follicular plugging, and atrophic sebaceous glands.17
Pathogenesis and histologic features The pathogenesis of postinflammatory hypopigmentation is not entirely clear but it probably involves alterations in the transfer of melanin from melanocytes to keratinocytes.1 The number of melanocytes usually remains within the normal range.
Histologically, there is focal reduction in pigmentation in the basal cell layer of the epidermis.
1002 Disorders of pigmentation