Pityriasis rosea

Pityriasis rosea is a common, acute, self limiting, papulo-squamous condition once thought to be due to HHV7 but there is now insufficient evidence to be certain of this (1).

The argument against an infectious cause includes the inability to identify an agent, lack of true epidemics, and inconsistent response to various studied antiviral and macrolide treatments (1)

Some drugs have been linked with an extensive and often prolonged form of the disease, such as captopril, barbiturates, clonidine, and gold (2).

The typical presentation is with fawn-coloured, large (around 2-10 cm in diameter), slightly raised, oval scaly patches which typically develop on the limbs and trunk - commonly known as an initial 'herald' lesion. Often there is a collarette of scale present at the margin in some lesions

Most commonly seen in children and young adults (2).

A systematic review concluded that "..When compared with placebo or no treatment, oral acyclovir probably leads to increased good or excellent, medical practitioner-rated rash improvement. However, evidence for the effect of acyclovir on itch was inconclusive. We found low- to moderate-quality evidence that erythromycin probably reduces itch more than placebo.." (3)

Click here for example images of pitryriasis rosea

Reference:

1. Chuh A, Chan H, Zawar V. Pityriasis rosea - evidence for and against an infectious aetiology. Epidemiol Infect. 2004 Jun;132(3):381-90.
2. Leung AKC, Lam JM, Leong KF, et al. Pityriasis rosea: an updated review. Curr Pediatr Rev. 2021;17(3):201-11.
3. Contreras-Ruiz J et al. Interventions for pityriasis rosea Cochrane Database Syst. Rev. 2019 Oct 30;2019(10):CD005068.