The nosology of parapsoriasis.

Parapsoriasis is a group of uncommon but not rare disorders that was created in 1902 as part of a now long forgotten scheme to classify all inflammatory dermatoses. This artificial grouping has led to an enormously confused nosology of these disorders, that are, for the most part, otherwise unrelated. The use of a number of different terms at different institutions and by different physicians to denote the same diseases, together with the use of particular, single terms to denote different diseases, has caused much unnecessary confusion. In this review these terms are examined and an attempt is made to propose a new, unambiguous classification. Using this system, physicians with different views regarding which of the parapsoriases constitute distinct entities should have not difficulty communicating, and should have clearer frame of reference within which to work. An attempt is made to evaluate critically which of the parapsoriases are distinct entities and whether one or more of them should be considered an early form of cutaneous lymphoma in light of currently available data.