Introduction

Pityriasis rosea describes an acute, self-limiting rash which tends to affect young adults.

Epidemiology

  • Incidence: 170.00 cases per 100,000 person-years
  • Peak incidence: 20-30 years
  • Sex ratio: more common in females 1:1
Condition Relative
incidence
Pityriasis rosea1
Guttate psoriasis0.03
<1 1-5 6+ 16+ 30+ 40+ 50+ 60+ 70+ 80+

Aetiology

The aetiology is not fully understood but is thought that herpes hominis virus 7 (HHV-7) may play a role.

Clinical features

Features
  • in the majority of patients there is no prodrome, but a minority may give a history of a recent viral infection
  • herald patch (usually on trunk)
  • followed by erythematous, oval, scaly patches which follow a characteristic distribution with the longitudinal diameters of the oval lesions running parallel to the line of Langer. This may produce a 'fir-tree' appearance

Examples of the hearld patch can be seen below:


The images below show the more widespread that follows:

Differential diagnosis

Differentiating guttate psoriasis and pityriasis rosea

Guttate psoriasisPityriasis rosea
ProdromeClassically preceded by a streptococcal sore throat 2-4 weeksMany patients report recent respiratory tract infections but this is not common in questions
Appearance'Tear drop', scaly papules on the trunk and limbsHerald patch followed 1-2 weeks later by multiple erythematous, slightly raised oval lesions with a fine scale confined to the outer aspects of the lesions.

May follow a characteristic distribution with the longitudinal diameters of the oval lesions running parallel to the line of Langer. This may produce a 'fir-tree' appearance
Treatment /
natural history
Most cases resolve spontaneously within 2-3 months
Topical agents as per psoriasis
UVB phototherapy
Self-limiting, resolves after around 6 weeks