Pityriasis rosea is a benign, self-limiting skin rash that usually occurs in adolescents and young adults. The cause is unknown, and the rash is not contagious. It usually only happens once in a lifetime.
Pityriasis rosea generally begins with one lesion on the trunk of the body: an oval, slightly raised spot about 2 to 5 centimetres in diameter, known as the herald patch. Over the next 1 to 2 weeks, smaller spots appear surrounding the herald patch and over the trunk, back, upper arms, and thighs. The spots generally clear on their own in 6 to 12 weeks. The herald patch is usually the last spot to clear.
The lesions of pityriasis rosea are pink or beige spots and bumps with a "collarette" of scaling skin surrounding each spot. The herald patch is much larger than the others, with a tawny or pink centre patch ringed by the collarette, which is then surrounded by an area of reddened skin. In about 75 per cent of cases, the lesions are itchy.
The spots of pityriasis rosea are scattered randomly across the front of the trunk and the upper parts of the legs and arms. On the back, they take on a characteristic "Christmas tree" pattern, with wider scattering of spots at the base of the spine and a narrower distribution at the top. Pityriasis rosea rarely appears on the face and neck.
The rash should resolve on its own within 3 months. If the lesions are itchy, oral antihistamines, anti-itch lotions or topical corticosteroids can be used. Some patients have relief from itchiness on exposure to sunlight. If the spots last longer than expected, a skin biopsy should be done to rule out other causes of the rash.
Some patients will experience a slight fever or fatigue at the onset of the rash. Exposure to heat or exercise may cause the spots to darken temporarily.
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- Taber's Cyclopedic Medical Dictionary; Clayton L. Thomas, M.D., M.P.H.; 1997
- The Merck Manual of Diagnosis and Therapy; Mark H. Beers, M.D. and Robert Berkow, M.D., editors; 1999