Pityriasis rosea

pityriasis rosea · herald patch · Christmas tree rash · PR

A single herald patch followed days to three weeks later by a truncal eruption in a young person - self-limiting, and the main job is to exclude syphilis.

DISCHARGEBand D

Red flags

Palm and sole involvement, or no itch with generalised lymphadenopathy - test for syphilis. Secondary syphilis is the classic mimic and is rising in incidence
Pregnancy - CKS notes that pityriasis rosea in the first trimester has been associated with adverse outcomes including miscarriage and premature delivery, while also advising that women should be reassured it is likely self-limiting and that in most cases there is no harm to the pregnancy. Discuss with obstetrics, and give both halves of that message rather than only the alarming one
An atypical morphology or distribution, or a course beyond about 5 months - reconsider the diagnosis, including a drug eruption or guttate psoriasis. Note that 2 to 3 months is the expected duration, not a prolonged one
A recent new drug - a pityriasis rosea-like drug eruption is well recognised
Systemic upset, which does not belong with this diagnosis

Recognise

On light skin

A single larger salmon-pink oval scaly herald patch, then crops of smaller pink oval plaques with a fine collarette of scale inside the edge, aligned along the ribs.

On brown and black skin

The salmon-pink colour does not translate, and lesions appear grey, dark brown, violaceous or hyperpigmented. Two variants are worth knowing: a papular form, and an inverse distribution involving the axillae, groins and face rather than the trunk - either of which means the classic fir-tree pattern may be absent entirely. Both are widely described as commoner in children and in brown and black skin, but no frequency figure is given here because none could be traced to a source read in full. The oval shape, the long axis following skin cleavage lines, and the trailing collarette of scale just inside the lesion edge are the tone-independent features - stretch the skin gently to bring out the collarette. Post-inflammatory hyperpigmentation and sometimes hypopigmentation are prominent and can last months after the eruption clears.

In any skin tone

Herald patch - a single larger lesion, typically 2 to 5 cm, appearing a few days to three weeks before the generalised rash, which CKS puts at up to 90% of people. Subsequent lesions are typically 0.5 to 1 cm, so the size difference is part of the pattern. A patch that appeared eighteen days ago still fits; its absence does not exclude the diagnosis
Oval lesions with the long axis along the ribs
A fine collarette of scale trailing inside the edge of each lesion
Mild or no systemic symptoms in a young person, typically 10 to 35 years old
Self-limiting, but slower than patients expect. CKS says new crops may continue for up to 6 weeks and the rash often worsens before it settles, and that it usually settles within 2 to 3 months, occasionally taking up to 5 months to disappear
Palms and soles are spared - if they are involved, think syphilis

Distribution

Trunk and proximal limbs, with the long axis of each oval lesion following the lines of the ribs - the 'Christmas tree' or 'fir tree' pattern on the back. Usually spares the face, palms and soles.

Photographs

Pityriasis rosea on dark skin, photographed over the back and shoulder. The lesions are dark, raised and scaly rather than the salmon-pink o — Pityriasis rosea on dark skin, photographed over the back and shoulder. **The lesions are dark, raised and scaly rather than the salmon-pink ovals of the textbook description**, and they follow the skin lines across the back. A papular, strongly pigmented presentation like this is described as commoner in brown and black skin, and it is the reason the diagnosis is so often missed here. Because it does not look like the picture in the book, **secondary syphilis has to be actively excluded** rather than dismissed on appearance.
Fitzpatrick IV-VI (Fitzpatrick type estimated from the photograph, not stated by the source) · Oladokun RE, Lehloenya RJ, Hlela C, Ubesie AC, Katibi SO, Malande OO, Eley BS · Atlas of Paediatric HIV Infection, UCT Libraries Press 2018 - Chapter 5: Inflammatory Skin Conditions, p106 · CC BY 4.0

Provenance for every photograph in this library: image licences. How much of the corpus still has no darker-skin photograph: skin tone coverage.

Mimics

Syphilis - the secondary rash — The one to exclude. Secondary syphilis involves palms and soles, does not itch, and has lymphadenopathy
Psoriasis, including guttate — Guttate psoriasis also gives a sudden truncal eruption in a young person, but lesions are thicker-scaled and there is no herald patch or collarette
Tinea corporis, cruris and pedis — The herald patch alone is frequently misdiagnosed as ringworm and treated with an antifungal
Drug eruptions - morbilliform and fixed — A pityriasis rosea-like drug eruption is recognised - check what is new
Seborrhoeic dermatitis — Both can give scaly truncal patches, but the oval shape and collarette distinguish this

What to do in the ED

Examine the palms and soles and ask about a preceding painless ulcer, and test for syphilis if there is any doubt - this is the single most important action on this page
Ask about pregnancy. If the patient is pregnant, discuss with obstetrics - and convey CKS's balanced position: an association with adverse outcomes in the first trimester, alongside reassurance that it is usually self-limiting and most pregnancies are unharmed
Review the drug history for a recent new medication
Explain the natural history, and be concrete about it: new crops are possible for up to 6 weeks, a rash that often worsens before it settles, and resolution usually within 2 to 3 months, occasionally up to 5. Itch is managed with emollient and a mild topical corticosteroid or an antihistamine
Warn about post-inflammatory pigment change, particularly in brown and black skin, so it is not mistaken for persisting disease
No investigation is needed in a typical case with a herald patch and a classic distribution

Disposition

DISCHARGE

Reassure and discharge with an explanation of the timescale. Test for syphilis where the distribution is atypical, and involve obstetrics in pregnancy.

Safety-netting

This clears by itself, but slowly - usually over two to three months, and occasionally up to five. New patches can keep appearing for up to six weeks and it often looks worse before it looks better; that is expected and is not a sign it is going wrong. Return if the rash appears on your palms or soles, if it is still there after about five months, if you become unwell, or if you are or might be pregnant. The darker or paler marks left behind afterwards will fade slowly and are not scars.

Sources

Open this entry in the interactive tool