QuestionSBA
QuestionChoice
Guttate psoriasis also presents with salmon pink plaques, most commonly on the torso. It is usually preceded by a respiratory infection 2-3 weeks previously. However, there is not usually a herald patch associated with guttate psoriasis
32959
b
Guttate psoriasis
QuestionChoice
Pityriasis rosea typically presents with a "herald patch". This can be preceded by prodromal symptoms such as fever or malaise. After 1-2 weeks, the secondary rash will appear, which is usually on the trunk and arms. This is symmetrical and classically described to be in the shape of a Christmas tree. Pityriasis rosea is usually self-limiting, is non-contagious and generally improves within 6 weeks. However, patients may require symptomatic treatment
32958
a
Pityriasis rosea
QuestionChoice
Erythema multiforme is a hypersensitivity reaction, usually to an infection or drugs. The rash starts peripherally and moves centrally, therefore, is unlikely in this case. The rash is made up of "target lesions", which are made up of concentric rings
32960
c
Erythema multiforme
QuestionChoice
Lichen planus is a skin disease with an unknown origin. It comprises pruritic, papular eruptions, most commonly on the genitals, flexor surfaces or mucous membranes. Therefore, it is unlikely in this patient
32962
e
Lichen planus
QuestionChoice
Tinea corporis is a dermatophytosis (tinea) infection that affects the trunk and arms. Dermatophytes are a group of fungi causing lesions that are usually annular, scaly and have a raised edge. Herald patches are not associated with tinea corporis
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d
Tinea corporis
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# Summary

Pityriasis rosea is a common rash that is characterized by a preceding **herald patch** - a single, large, discoid (coin-shaped), erythematous patch. This patch classically has a 'collarette' of scale just inside the edge of the lesion. A few days later a widespread rash appears across the trunk consisting of multiple small, erythematous, scaly patches (similar but smaller than the herald patch). These lesions are classically distributed across the trunk in a **'christmas tree' pattern**. There are associations with viral infections and drugs. The condition is self-limiting and resolves without any treatment.

# Definition

A self-limiting rash that resolves after 10 weeks characterised by a herald patch and subsequent fir-tree pattern eruption

# Pathophysiology

Triggers of pityriasis rosea:

- Viruses: such as HHV6/7, COVID-19, and Flu
- Drugs: such as gold, ACEi, penicillamine, and biologics. 
- Many vaccines: BCG, hepatitis B, and pneumococcal. 
	
# Clinical Features

- Usually, a few days after a viral infection e.g. an URTI, the patient presents with a 'herald patch.'
- This is a red-pink oval/discoid plaque with a peripheral colarette of scale on the trunk or upper arm/thigh. It may be misdiagnosed as ringworm.
- 1-20 days later, a similar widespread eruption (but the individual lesions may be smaller) occurs on the body that follows a fir tree (Christmas tree) pattern appears, with the long axis of the lesions sweeping from back to front as if following Langer's lines.
- In most cases, there are virtually no symptoms except for the rash.

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# Treatment

- 25% patients may have intense pruritus. Antihistamines, emollients, and topical steroids may be of use in these patients. It is self-limiting and will resolve on its own. 

# NICE Guidelines

[Click here for NICE CKS on pityriasis rosea](https://cks.nice.org.uk/topics/pityriasis-rosea/)
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Pityriasis rosea
Topic
60
General Practice
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An 18-year-old female sees her GP with an itchy rash. Two weeks previously the patient had a fever and noticed a 5cm diameter, oval, salmon pink patch near her umbilicus. On examination, the rash now covers the majority of her torso. It is made up of multiple millimetre to centimetre wide, salmon pink patches.

What is the most likely diagnosis?
a