Abstract
Pityriasis rosea, first described in 1860 by Gibert, is a common acute inflamatory disorder. Both its etiology and pathomechanism still remain unclear. Some confusion still persists over atypical cases and differential diagnoses of other familiar skin disorders such as acute guttate psoriasis, seborrheic dermatitis and parapsoriasis with generalized eruption. So far, histologic findings have not been helpful for making an accurate diagnosis because of their close resemblance to other dermatitis-eczema groups. The plasminogen activator, which converts plasminogen into plasmin, has been detected in the psoriatic epidermis. It may thus possibly be involved in one of the pathomechanisms of psoriasis. Plasminogen activator activity in the epidermis of the present 6 cases of pityiasis rosea was detected using a film of fibrin, i. e., Todd’s method, however this activity was not detected in the epidermis of seborrheic dermatitis and eczema groups. The striking histologic features in all the 6 cases were the absence of a granular layer. However, the epidermis of skin biopsy specimens of the 9 cases initially diagnosed as pityriasis rosea, in which epidermal plasminogen activator activity was not detected, showed a remaining granular layer. Whether the difference between the present two groups of pityriasis rosea is either a stage or an activity of the disease remains to be fully elucidated. Further studies should be conducted to clarify all the pathomechanisms involved in pityriasis rosea.
