An accurate description of the lesions and the course of psoriasis vulgaris is given as a definition of the disease in most of the old and modern textbooks on dermatology, but psoriasis vulgaris, as the name implies, is the common variety. Unusual manifestations of the disease may occur simultaneously with the ordinary type, or rare forms may exist without the presence of the ordinary lesions which would aid in identifying the bizarre manifestations. When such rare forms appear alone, diagnosis is often difficult and opinions must be separated from facts.
Obviously the morphology and the histology of the lesions offer the only basis upon which to make a diagnosis. There is a tremendous variation in the morphology of the odd forms of psoriasis, and if one has a large experience with the histopathology of the disease one knows only too well that what to the casual histologist
MICHELSON HE. The Unusual in Psoriasis. AMA Arch Derm. 1958;78(1):9–13. doi:10.1001/archderm.1958.01560070011002
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