Pityriasis Rosea: A Comprehensive Classification.

Pityriasis rosea (PR) is an acute, self-limiting exanthematous disease associated with the endogenous systemic reactivation of human herpesvirus (HHV)-6 and/or HHV-7. The disease typically begins with a single, erythematous plaque followed by a secondary eruption with lesions on the cleavage lines of the trunk (configuration of a 'Christmas tree'). The duration may vary from 2 weeks to a few months. Besides the typical presentation of PR, atypical forms have been described. The previous classifications of PR are mainly based on its atypical morphological features rather than on the pathogenetic mechanisms that underlie the different presentations of the disease. Notably, most of the morphologically atypical forms follow a course amenable to the classic form. The classification that we propose, taking into account the pathogenesis, clinical features, and course of the disease, is easy and intuitive and may be helpful in identifying the atypical forms of PR in order to avoid misdiagnosis and establish the best treatment options. Finally, this classification provides indications for managing potentially harmful forms of PR (such as PR in pregnancy) and PR-like eruptions.