Pityriasis rosea, granuloma annulare, and lichen planus are unique inflammatory conditions of unknown etiology. Each has various clinical presentations and distinctive patterns of distribution. Most often the diagnosis can be readily made clinically based upon the typical signs and symptoms of these rather curious dermatoses.

There are conflicting reports about the association of these entities with certain infectious and metabolic conditions. For example, pityriasis rosea is thought to represent a viral exanthem caused by a herpesvirus. An association has been noted between lichen planus and hepatitis C, chronic active hepatitis, and primary biliary cirrhosis; and widespread granuloma annulare is considered by some investigators to be associated with diabetes mellitus.