QuestionSBA
QuestionChoice
While psoriasis may also present with scaly, itchy patches on the skin, it is typically more persistent and chronic than pityriasis rosea. It is also more likely to affect other areas of the body, such as the scalp, nails, and joints. In addition, psoriasis is typically accompanied by other physical findings, such as thickened, pitted nails and red, swollen joints.
62334
b
Psoriasis
QuestionChoice
Eczema, also known as atopic dermatitis, is a chronic skin condition that typically presents with red, itchy patches on the skin. However, eczema tends to affect areas of the body that are more prone to irritation, such as the face, neck, and inner elbow, rather than the chest and abdomen. Eczema is also more likely to be chronic and persists over time rather than resolving on its own within a few weeks as pityriasis rosea does.
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Eczema
QuestionChoice
Tinea corporis is a dermatophyte infection of the face, trunk, and extremities. It is often confused with the herald patch of pityriasis rosea. The distinguishing features of tinea corporis are a less severe involvement of the centre of the lesion, a more active edge and itching. In contrast, circular patches of scaling and erythema are clues to pityriasis rosea.
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Tinea corporis
QuestionChoice
The symptoms described in the clinical scenario are consistent with pityriasis rosea, a skin condition probably due to human Herpesviruses 6 and 7. It typically starts with a single patch (herald patch) on the trunk or neck, which is oval, 2-5cm in size, and has a central, salmon-coloured area and a dark-red peripheral zone separated by fine scales. A secondary rash of smaller patches follows, with a "Christmas tree" distribution on the trunk, neck, and upper limbs.
62333
a
Pityriasis rosea
QuestionChoice
Allergic dermatitis, also known as contact dermatitis, is a skin reaction to an allergen or irritant. It is characterised by red, itchy patches on the skin that may be accompanied by swelling and blistering. Allergic dermatitis may be triggered by exposure to certain substances, such as chemicals, fragrances, or metals. However, the sudden onset and lack of other physical findings make allergic dermatitis less likely in this case.
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Allergic dermatitis
Concept
Chapter
# 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
12528
A 30-year-old woman presents to the GP clinic with a mildly itchy rash on her chest and abdomen, which consists of pink scaly patches. The patient reports that the rash appeared suddenly about a week ago and has not improved since. On examination, the rash is salmon-coloured, oval, and has a surrounding ring of scale. It has a characteristic "Christmas tree" distribution.

What is the most likely diagnosis?
a