Pityriasis Rosea at a Glance
- Common acute papulosquamous eruption normally lasting 4–10 weeks.
- Most often begins as a single 2- to 4-cm thin oval plaque with a fine collarette of scale located inside the periphery of the plaque (“herald patch”).
- Similar-appearing, but smaller, lesions appear several days to weeks later, typically distributed along the lines of cleavage on the trunk (“Christmas tree” pattern).
- Usually asymptomatic, sometimes pruritic with mild flu-like symptoms.
- Occurs most commonly in teenagers and young adults.
- Probably a viral exanthem associated with reactivation of human herpes virus (HHV)-7 and sometimes HHV-6.
- Treatment is usually supportive, although midpotency topical corticosteroids can reduce pruritus; high-dose acyclovir for 1 week may hasten recovery.
The term pityriasis rosea (PR) was first used by Gibert in 1860 and means pink (rosea) scales (pityriasis).1 PR is a common acute, self-limited skin eruption that typically begins as a single thin oval scaly plaque on the trunk (“herald patch”) and is typically asymptomatic. The initial lesion is followed several days to weeks later by the appearance of numerous similar-appearing smaller lesions located along the lines of cleavage of the trunk (a so-called Christmas tree pattern). PR most commonly occurs in teenagers and young adults, and is most likely a viral exanthem associated with reactivation of human herpes virus 7 (HHV-7) and sometimes HHV-6,2–5 the viruses responsible for rubeola (see Chapter 192). Possible treatment may focus on associated pruritus. One study suggests that administration of high-dose acyclovir for 1 week, if initiated early in the disease course, hastens recovery from PR.6
PR is reported in all races throughout the world, irrespective of climate.7–9 The average annual incidence at one center was reported to be 0.16% (158.9 cases per 100,000 person-years).9 Although PR is usually considered to be more common in the spring and fall months in temperate zones, seasonal variation has not been borne out in studies performed in other parts of the world. Clustering of cases can occur and has been used to support an infectious etiology for PR, although this is not a consistent feature observed in all communities.8 Most studies have shown a slight female preponderance of approximately 1.5:1.7,9 PR most commonly occurs between the ages of 10 and 35 years.9 It is rare before age 2 years and after age 65 years. Recurrences of PR are rare, which suggests lasting immunity after an initial episode of PR.
Historically, PR has been considered to be caused by an infectious agent, given (1) the resemblance of the rash to known viral exanthems; (2) rare recurrences of PR that suggest lifelong immunity after one episode; (3) occurrence of seasonal variation in some studies; (4) clustering in some communities; and (5) the appearance of flu-like symptoms in a subset of patients. Numerous studies over the past 50 years have explored various pathogens as possible causes of ...