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Dermatopathology: Practical & Conceptual July - September 2002
Prurigo Pigmentosa: New Observations and Comprehensive Review
Almut Böer, M.D.
Noriyuki Misago, M.D.
Manfred Wolter, M.D.
Hiromaro Kiryu, M.D.
Xiao Dong Wang, M.D.
A. Bernard Ackerman, M.D.
Differential Diagnosis Clinically
Differential Diagnosis Histopathologically
Of course, lesions of prurigo pigmentosa must appear first as erythematous macules, rather than as papules, and, moreover, it is unlikely in the extreme that any of the papules actually subside completely in two days (only urtica involutes that quickly and the papules of prurigo pigmentosa are urticarial, not urtica). The pigmentation is post inflammatory, that is, a residuum of the effects of the infiltrates of inflammatory cells on the epidermis, from whence melanin is lost to macrophages in the upper part of the dermis; red papules resolve as pigmented macules. In order for pigment to appear in reticular pattern, weeks, at least, must go by and the phenomenon can be explained not only by the fact that the urticariaal papules erupt in a somewhat reticulated pattern, but by the reality that each crop of papules in a recurrent eruption, upon involuting, contributes to the netlike pattern of pigmentation.
As the number of reports of patients with prurigo pigmentosa increased, the ratio of females to males has declined continually, that is, from 6:1 recorded by Nagashima in 1978
to 2:1 when data from all of the articles published to date are pooled. Prurigo pigmentosa still appears to be more common in females, but sex, alone, cannot be used as a criterion for diagnosis or in differential diagnosis.
None of the authors of articles have commented on the lack of appropriateness of the name "prurigo pigmentosa", a designation that fails to enlighten because it is but one of hundreds of diseases of the skin that are itchy and resolve with pigmentation. Neither should prurigo pigmentosa be conceived of simply as one of the "pruriginous dermatoses", which, in actuality, are not a distinct group of inflammatory diseases but rather variations on the theme of lichen simplex chronicus. Prurigo pigmentosa is a distinctive inflammatory skin disease that arises
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