History and exam

Key diagnostic factors

common

herald patch

This is the largest lesion and the first to arise, usually on the trunk. It begins as a single papule and expands into a pink erythematous oval patch or plaque up to 10 cm in diameter, with raised border and scale.[3]

Precedes eruption by up to 2 weeks usually, but delay of up to 84 days has been reported.[4] It is found in up to 80% of cases.[4][8] Multiple herald patches are found in about 2% of cases.[17]

[Figure caption and citation for the preceding image starts]: Herald patch in classic distribution on the upper torsoFrom the collection of Daniela Kroshinsky, MD, MPH; used with permission [Citation ends].com.bmj.content.model.Caption@17e25be1

pruritus

This is moderate to severe in 50% of cases; absent in 25%.[7][12]

age 10 to 35 years

Although PR is reported in all ages (from infants to older adults), most affected people are aged 10 to 35 years old.[10][11]

2- to 12-week duration

Self-limiting condition. Lesions usually resolve over 2 to 12 weeks, but may rarely be present for as long as 5 months.[3][12]

scale

Fine scale may be present in the centre of the herald patch, within raised border with free edge inside (collarette).[7][12]

located on trunk and upper extremities

The most common site of lesions.[12]

fir-tree pattern distribution

Long axes of the oval lesions are aligned along lines of skin cleavage ('Langer lines') on the trunk, creating a fir-tree pattern of branches with the spine as the trunk.[3]

V distribution over the chest and upper back, circumferential over the shoulders and hips, horizontal over the lower trunk.[7]

uncommon

located on face, palms, soles, mucosa

Uncommon in adults, but is seen more often in children.[3][4][12][21]

acute to sub-acute recurrent skin eruption

Recurrences can occur in 2.8% of cases.[12]

Other diagnostic factors

common

2-week timing between herald patch and new lesions

Herald patch followed within 2 weeks by new lesions that increase in number over the next 2 to 6 weeks before resolving.[12]

female sex

Male-to-female ratio is 1:1.43.[4][12]

uncommon

prodromal symptoms

Include fever, malaise, headache, and arthralgia. Occur in 5% of cases.[2][3][7]

pigmentary alteration (severe cases/dark skin colour)

Previous PR usually heals without scarring, but can leave pigmentary alteration in severe cases or in patients with dark skin colour.[22]

Risk factors

weak

age 10 to 35 years

Pityriasis rosea is most common in people aged 10 to 35 years.[10][11]

female sex

Male-to-female ratio is 1:1.43.[4][12]

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