Pityriasis Rosea

Introduction

Pityriasis rosea is a common, self-limiting skin condition characterised by a distinctive rash that typically begins with a single large patch, known as the "herald patch," followed by the development of smaller secondary lesions. It most commonly affects adolescents and young adults and is usually asymptomatic, though some patients may experience mild itching. The condition generally resolves on its own within 6-8 weeks.

Aetiology

The exact cause of pityriasis rosea is not fully understood, but it is believed to be associated with a viral infection, most likely human herpesvirus 6 (HHV-6) or human herpesvirus 7 (HHV-7). It is not considered to be highly contagious, and it often occurs in clusters, suggesting a possible viral etiology.

Clinical Presentation

Pityriasis rosea typically presents with the following features:

• Herald Patch: The condition usually begins with a single, large, oval or round, pink or red patch on the trunk, known as the herald patch. This patch is usually 2-10 cm in diameter and may be mistaken for ringworm (tinea corporis).
• Secondary Rash: Within 1-2 weeks of the herald patch, multiple smaller lesions (2-3 cm) appear on the trunk and proximal limbs. These lesions are also oval in shape and tend to follow the lines of skin cleavage, creating a "Christmas tree" pattern on the back.
• Colour and Scaling: The lesions are usually pink, red, or fawn-coloured and may have a fine, scale-like border, giving them a characteristic "collarette" of scale.
• Pruritus: Itching is mild to moderate in some cases, though many patients experience no pruritus at all.
• Absence of Systemic Symptoms: Unlike other viral exanthems, pityriasis rosea is generally not associated with systemic symptoms like fever or malaise.

Diagnosis

The diagnosis of pityriasis rosea is primarily clinical, based on the characteristic appearance of the rash. However, the following may be considered in the diagnostic process:

• Clinical History and Examination: The presence of a herald patch followed by the secondary rash in a "Christmas tree" pattern is often sufficient for diagnosis.
• Differential Diagnosis: It is important to distinguish pityriasis rosea from other conditions such as tinea corporis, psoriasis, drug eruptions, and secondary syphilis. A history of recent medication use or sexual exposure may warrant further investigation.
• KOH Test: If tinea corporis is suspected, a potassium hydroxide (KOH) preparation can be performed to rule out fungal infection.
• Serological Testing: If secondary syphilis is a concern, particularly in sexually active patients, serological tests (e.g., VDRL, RPR) should be conducted to rule out syphilis.

Management

Pityriasis rosea is a self-limiting condition, and most cases resolve spontaneously within 6-8 weeks. Management is primarily focused on symptom relief:

• Reassurance: Patients should be reassured that the condition is benign, self-limiting, and does not typically require aggressive treatment.
• Topical Emollients: Emollients can be used to soothe dry skin and reduce itching.
• Topical Corticosteroids: Low-potency topical corticosteroids (e.g., hydrocortisone 1%) may be used to alleviate itching if it is bothersome.
• Antihistamines: Oral antihistamines, such as cetirizine or loratadine, can be used for symptomatic relief of itching.
• Avoiding Triggers: Patients should avoid irritating soaps, hot baths, and heavy sweating, which may exacerbate the rash.

In rare cases where the rash is extensive or symptoms are severe, the following may be considered:

• Phototherapy: Narrowband UVB phototherapy may be considered for severe or persistent cases, though it is rarely needed.
• Antiviral Therapy: While not routinely recommended, antiviral medications (e.g., acyclovir) have been used anecdotally in cases where a viral etiology is strongly suspected.

When to Refer

Referral to a dermatologist may be necessary in the following situations:

• Uncertain Diagnosis: If the diagnosis is unclear or if the rash does not follow the typical course of pityriasis rosea, referral for further evaluation is recommended.
• Severe or Atypical Cases: Referral may be warranted for cases that are severe, persistent, or atypical in presentation.
• Secondary Infection: If there is concern about a secondary bacterial infection, specialist advice may be needed.

References

1. British Association of Dermatologists (2024) Pityriasis Rosea: Patient Information Leaflet. Available at: https://www.bad.org.uk (Accessed: 26 August 2024).
2. National Institute for Health and Care Excellence (2024) Management of Pityriasis Rosea. Available at: https://www.nice.org.uk/guidance/ng23 (Accessed: 26 August 2024).
3. British National Formulary (2024) Topical and Oral Treatments for Dermatological Conditions. Available at: https://bnf.nice.org.uk/ (Accessed: 26 August 2024).