Pityriasis rosea

Pityriasis rosea describes an acute, self-limiting rash which tends to affect young adults. The aetiology is not fully understood but is thought that herpes hominis virus 7 (HHV-7) may play a role.

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

Management

• self-limiting - usually disappears after 6-12 weeks

Differentiating guttate psoriasis and pityriasis rosea

_ Guttate psoriasis _ Pityriasis rosea| Prodrome _ Classically preceded by a streptococcal sore throat 2-4 weeks_ Many patients report recent respiratory tract infections but this is not common in questions | Appearance _ 'Tear drop', scaly papules on the trunk and limbs _ Herald 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 |