Pityriasis rosea is a fascinating disease. Its usual occurrence on the trunk and on the upper region of the extremities is only one of the different forms in which the disease may be expressed. This is apparent from the following classification of pityriasis rosea that I suggested in a previous publication1:
Although the face, neck, forearms, and legs are usually exempt, these parts may be involved with or without involvement of the trunk; indeed, no region of the skin is exempt (Fig. 1). The palms and soles, usually spared, may be affected, in which event the eruption is more likely to be accompanied with vesicles (Fig. 2).
There are a number of curious features of the disease. What is the significance of the herald or primitive patch? Why do lesions follow the lines of cleavage of
KLAUDER JV. Does the Tanned Skin Prevent Eruption of Pityriasis Rosea? Discussion of Fallacy in Reasoning, Importance of Control Study. AMA Arch Derm. 1957;76(2):200–205. doi:10.1001/archderm.1957.01550200044009
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