Definition:

Pityriasis rosea (PR) is an acute exanthem, which prevalently affects children and young adults. The cause of PR is uncertain but epidemiological (seasonal variation and clustering in communities) and clinical features suggest an infective agent. Light and electron microscopy findings suggest infection with human herpesviruses 6 and 7 (HHV-6/7). HHV-6 and HHV-7 may also interact with each other, explaining recurrences and atypical presentations. PR is self limiting and resolves within one to three months. It typically starts with the development of a large erythematous scaly plaque also called the herald patch or mother patch on trunk or neck, which is followed by an eruption of multiple secondary small erythematous scaly lesions located predominantly on the trunk and following the lines of cleavage on the back (Christmas tree or inverted fir tree appearance). Collarette scaling is seen typically. The eruption is usually preceded by a prodrome of sore throat, gastrointestinal disturbance, fever, and arthralgia. A case of PR is diagnosed mainly on clinical grounds. A biopsy is needed in atypical cases, and it mainly helps in excluding other differentials rather than diagnosing PR as the histopathological examination in a case of PR is relatively nonspecific and resembles a subacute or chronic dermatitis. As PR is a self-limiting disorder, most patients just need to be counseled regarding the natural course of the disease instead of putting them on an aggressive treatment protocol. Most patients would just need emollients, antihistaminics, and sometimes topical steroids to control pruritus.