Peer Reviewed
AUTHOR:
Kirk Barber, MD, FRCPC––Series Editor
Alberta Children’s Hospital
CITATION:
Barber K. Does this patient have psoriasis? Consultant. 2007;6(1):20,22.
A 17-year-old boy presents with a red, scaly rash on his trunk that began as a single lesion on his left flank. The generalized eruption had developed within 24 to 48 hours. The patient's father has psoriasis.
Does this patient also have psoriasis, or is this skin condition unrelated?
Answer and discussion on next page.
This young man has pityriasis rosea. The hallmark of this condition is the herald patch (arrow),which is thought to be present in 40% to 60% of all patients with pityriasis rosea. It is usually a solitary, round, or oval lesion that can occur anywhere; however, it is predominantly found on the upper arms and trunk. When the herald patch first occurs, it does present the possibility of tinea corporis or a single patch of psoriasis. However, the development of a generalized eruption within a week is quite characteristic of pityriasis rosea.
The secondary eruption is of similar morphology to the herald patch, but the lesions are usually much smaller. Lesions number from few to many and usually appear within 1 to 2 weeks of the herald patch. Individual lesions have a collarette scale, with the scale attached at the periphery and the free edge pointing inward.
Their typical distribution has been termed T-shirt and shorts. Fewer than 15% of affected patients have involvement distal to the elbows and knees. The face is generally spared, as are the palms and soles. The characteristic distribution on the trunk has been described as an inverted-Christmas tree pattern, with the oval lesions running parallel to the ribs. I have found it useful to examine the axillae, where the oval lesions form an arciform pattern.
Half of patients with pityriasis rosea report moderate to severe itching. This is usually controllable with mid- to high-potency topical corticosteroids applied to individual lesions with the addition of systemic antihistamines. Phototherapy with UV-B light or significant sun exposure can also be helpful.
Pityriasis rosea generally resolves spontaneously at about 12 weeks. The eruption usually occurs once in a lifetime, but about 2% to 3% of patients experience a relapse.
There are multiple variants of pityriasis rosea. The most common is inverse pityriasis rosea, in which the lesions occur only in the flexural areas. The morphology is similar and the diagnosis is made on the basis of the linear array of lesions of typical morphology. The humidity in most flexural areas minimizes the presence of collarette scales.
Dr Barber is a consultant dermatologist at Alberta Children’s Hospital and clinical associate professor of medicine and community health sciences at the University of Calgary in Alberta.
