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 lasts for approximately 2-6 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.¹

Epidemiology

• The overall prevalence is approximately 0.15%.²
• Pityriasis rosea is most common in children and young adults, with 15-40 years being the peak age range affected. Pityriasis rosea is rare in infants and in the elderly.
• Occurs most often during the spring and autumn.
• No bacteria, virus, or fungus has been isolated as a cause but human herpes viruses 6 and 7 may play a role.²
• Some drugs, e.g. bismuth, barbiturates, captopril, gold, metronidazole, D-penicillamine and isotretinoin occasionally cause a drug-induced pityriasis rosea.

Presentation

• There may be prodromal symptoms, e.g. malaise, nausea, anorexia, fever, joint pain, lymph node swelling, headache, that precede the appearance of the herald patch.
• Pruritus (may be intense) occurs in the majority of patients.
• The herald patch measures 1-2 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 a minority of patients, the herald patch is either absent or confluent with the other lesions.
• Variant presentations include peripheral distribution of the rash, and facial involvement may be seen in children. Skin lesions may also be large, urticarial, vesicular, pustular, purpuric, and resemble erythema multiforme.
• Hypopigmentation and hyperpigmentation of affected skin may follow the inflammatory stage. Hyperpigmentation is more common In patients with black skin.
• Oral lesions are rare but may occur, e.g. erythematous plaques and ulcers.

Differential diagnosis

• Erythema multiforme
• Pityriasis alba
• Guttate psoriasis
• Secondary syphilis
• Tinea corporis
• Nummular eczema
• Seborrhoeic dermatitis
• Drug eruptions
• Erythema migrans
• Lichen planus
• Pityriasis lichenoides
• Kaposi's sarcoma

Investigations

• Diagnosis is clinical and usually no investigations are required.
• Skin biopsy may be required to confirm or alter the diagnosis.
• Other investigations, e.g. syphilis serology, may be required to rule out other possible diagnoses.

Management

• Pityriasis rosea is a self-limiting disease, and treatment is supportive.
• Exposure to sunlight is helpful.
• Topical zinc oxide and calamine lotion are useful for pruritus.
• Pruritus can also be treated with topical corticosteroids, oral antihistamines or antipruritic lotions.
• Oral erythromycin may be effective in treating the rash and decreasing the itch.³

Prognosis

• It usually lasts for 6-8 weeks before clearing spontaneously.
• Fewer than 3% of affected individuals experience recurrences.²