Integration: Unifying Concept
Pityriasis rosea is a distinctive, probably virally-induced disease that has typical morphologic features, clinically and histopathologically. By microscopy, a tissue section of a biopsy specimen from a scaly papule of pityriasis rosea shows a superficial perivascular infiltrate of lymphocytes, variable numbers of extravasated erythrocytes in an edematous papillary dermis, a slightly hyperplastic epidermis that houses foci of spongiosis, and mounds of parakeratosis. The findings histopathologic in pityriasis rosea are indistinguishable from those of erythema annulare centrifugum.
In some black patients with pityriasis rosea, vesicles may develop clinically, and they are seen by conventional microscopy to be the result of extensive spongiosis. As a rule, however, lesions of pityriasis rosea do not vesiculate.