Pityriasis rosea

Pityriasis rosea is an acute, self-limiting skin condition. A primary plaque ('herald patch') is followed by a distinctive, generalised itchy rash 1-2 weeks later.

The rash typically lasts for approximately 5-8 weeks. Lesions are typically oval, dull pink or tawny and appear in a 'Christmas tree' distribution, usually on the trunk and the upper arms and legs.

Aetiology¹

The cause is unknown but it is believed to be infective in origin due to factors such as seasonal and geographical clustering.

No bacterium, virus, or fungus has been isolated as a cause but human herpesviruses 6 and 7 may play a role.

Pityriasis rosea-like drug eruptions have been associated with numerous medications, including:

• Angiotensin-converting enzyme inhibitors.

• Antibiotics (such as metronidazole) and antifungals (such as terbinafine).

• Non-steroidal anti-inflammatory drugs (NSAIDs).

• Antidepressants and anxiolytics, such as nortriptyline, bupropion and barbiturates.

• Vaccines.

• Lithium.

• Lamotrigine.

• Atenolol.

• Omeprazole.

• Biologics such as imatinib, adalimumab and etanercept.

Epidemiology^{1 2}

• Pityriasis rosea is most common in children and young adults, aged 10-35 years. It is more common in women (with a female-to-male ratio of 1.4:1).

• Pityriasis rosea is rare in infants and young children and in the elderly.

• Prevalence in the community has been estimated to be around 1.3%.

• It occurs most often during the spring and autumn.
  

Presentation

Pityriasis rosea on the abdomen

By Marekzerzan (Own work), CC BY-SA 4.0, via Wikimedia Commons

Several images of the rash of pityriasis rosea are available on the DermNet NZ site³ .

Clinical features¹

• There may be prodromal symptoms (eg, malaise, nausea, anorexia, fever, joint pain, lymph node swelling and headache) that precede the appearance of the herald patch.

• Pruritus (may be intense) is thought to occur in about half of cases.

• The rash begins with a herald patch in 40-76% of cases. The herald patch measures 2-5 cm in diameter and is oval or round with a central, wrinkled, salmon-coloured area, separated from a dark-red peripheral zone by fine scales. The herald patch is usually located on the trunk but may be seen on the neck or extremities.

• The secondary rash is symmetrical and localised, predominantly to the trunk, neck and proximal extremities.

• The lesions of the secondary rash are small versions of the herald patch, with the two red zones separated by a scaling ring. They are distributed in a 'Christmas tree' pattern.

• In some cases, the herald patch is either absent or confluent with the other lesions. In others, there are multiple herald patches.

• Variant presentations include peripheral distribution of the rash; facial involvement may be seen in children. Skin lesions may also be large, urticarial, vesicular, pustular, and purpuric, and resemble erythema multiforme.

• Hypopigmentation and hyperpigmentation of affected skin may follow the inflammatory stage.

• Oral lesions are rare but may occur - eg, erythematous plaques and ulcers.

Differential diagnosis²

• Guttate psoriasis.

• Erythema multiforme.

• Pityriasis versicolor.

• Pityriasis lichenoides.

• Tinea corporis.

• Discoid (nummular) eczema.

• Seborrhoeic dermatitis.

• Drug eruptions.

• Erythema migrans.

• Lichen planus.

• Polymorphic eruption of pregnancy.

• Secondary syphilis.

• Kaposi's sarcoma.

• HIV seroconversion (usually associated with a febrile, flu-like illness).

Investigations

• Diagnosis is clinical and usually no investigations are required.

• Skin biopsy is not usually advised but may be occasionally required to confirm or alter the diagnosis.

• Other investigations - eg, syphilis serology - may be required to rule out other possible diagnoses.

Management^{1 2}

Pityriasis rosea is a self-limiting disease. Treatment is symptomatic and only if required. Reassure the person that the rash will disappear on its own but that it may take a few weeks to do so. Explain that new areas may be affected by the rash for up to six weeks. Also reassure that it is not contagious.

There is no convincing evidence of efficacy for any treatments used. For pruritus the following may be tried:

• Emollients.

• Topical corticosteroid, with the potency depending on the severity of the itch.

• Topical menthol.

• A sedative antihistamine at night such as hydroxyzine or chlorphenamine.

Referral

Refer to a dermatologist if:

• The rash persists for more than three months.

• Itch is severe.

• Diagnosis is not clear.

Although the evidence of efficacy is not yet clear, phototherapy is often used in secondary care.

Oral aciclovir has been shown to be effective in terms of rash improvement. Erythromycin may be effective in improving the itch⁴ .

Pregnancy

There is believed to be a risk of viral reactivation in pregnancy, due to the change in immune response. Consequently, there appears to be an increased risk of miscarriage for women who develop pityriasis rosea in early pregnancy - closer follow-up may be required⁵ . However, this is based on evidence from a small case series only.

Prognosis²

• The eruptions are self-limiting and usually disappear gradually in 2-12 weeks, without any treatment.

• However, they can take up to five months to disappear in some cases.

• New skin lesions may continue to appear in the first 2-6 weeks.

• After lesions have disappeared, there may be some darkening or lightening of the affected skin for several months.

• It typically heals without scarring.

• Most people who have pityriasis rosea will not have another attack during their lifetime; the risk of recurrence is 2-3%.