Pink, scaly rash on 
the trunk and arms


  • Pityriasis rosea_0612 Derm Clinic 2

A woman, age 35 years, presented to the dermatology clinic with a two-week history of a scaly rash on her trunk and arms. According to the patient, the rash first started with one spot on the arm. Within a few days, it had spread to the chest, abdomen and back.

The rash was mildly pruritic at times. The woman denied any other symptoms of systemic illness and reported no prior medical or medication history. Physical examination revealed multiple discrete salmon and pink-colored oval-shaped scaly plaques scattered over the trunk and proximal arms.

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Pityriasis rosea (PR) is a common inflammatory exanthem that is generally self-limiting. Although there are no known causes, many studies report a temporal clustering of cases,1 suggesting an infectious etiology, with human herpesvirus (HHV)-6 and HHV-7 most frequently suspected.2 Some...

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Pityriasis rosea (PR) is a common inflammatory exanthem that is generally self-limiting. Although there are no known causes, many studies report a temporal clustering of cases,1 suggesting an infectious etiology, with human herpesvirus (HHV)-6 and HHV-7 most frequently suspected.2 Some patients provide a recent history of such mild constitutional symptoms as malaise and fatigue, compatible with a viral illness. Despite this theory, the rash does not appear to be contagious.

The rash appears most often in teenagers and young adults, with a greater female incidence. Interestingly, pregnant women appear to be affected at a greater rate. PR is rare in infants and the elderly. Incidence is highest during the spring and autumn months.

Given its unique characteristic appearance, PR is usually diagnosed based on physical examination alone. The rash usually starts with a single 1- to 10-cm scaly plaque, termed the herald or mother patch, which can persist for a week or more before subsequent lesions appear. Although the diagnosis can be challenging at this early stage of the disease, it becomes clearer as the rash progresses. New lesions multiply rapidly, are usually smaller than the herald patch, and average 5 mm to 10 mm in diameter.

Careful examination of the fully developed eruption reveals oval-shaped salmon-colored plaques with an overlying fine scale that often desquamates and leaves a characteristic collarette of scale. In addition, the lesions are usually arranged along the lines of cleavage. This characteristic pattern is commonly referred to as a “Christmas tree” or “fir tree” distribution. The rash most often appears on the trunk and upper extremities and usually spares the sun-exposed areas.

Rarely are the palms, soles, scalp, or penis involved. Typically, no other skin pathology is noted, although oral aphthous ulcerlike lesions have been associated with the rash.3

Atypical cases of PR present a diagnostic challenge. The rash may primarily involve the extremities and spare the trunk. Localized forms may occur and involve one area only, such as the neck, thighs, groin or axillae.4 An inverse distribution that spares the covered areas is very rare. Some patients present with a herald patch only, and no subsequent lesions appear.

The differential diagnoses for classic PR are most commonly tinea, secondary syphilis, erythema annulare centrifugum (EAC), nummular eczema and guttate-type psoriasis. Tinea versicolor is primarily seen on the trunk and proximal upper extremities; when this condition presents with hyperpigmented pink patches it can be hard to differentiate from PR. A fungal scraping can rule out tinea versicolor.

Secondary syphilis should always be considered and tested for in sexually active adolescents and young adults with a scaly annular rash. PR is often confused with EAC, as both rashes consist of oval scaly plaques with a peripheral collarette of scale.

If the diagnosis is uncertain, a skin biopsy can be performed. Histopathology of PR lesions shows features of a subacute or chronic eczematous dermatitis. The finding of a decreased or absent granular cell layer, erythrocytes in the papillary dermis, homogenization of the papillary dermal collagen, and the presence of dyskeratotic cells within the epidermis are all features suggestive of PR.5

No treatment is needed for the rash of PR, as the natural history is that of complete resolution. Average duration of the exanthem appears to be between four and seven weeks. At times, the rash may resolve with remaining postinflammatory hyperpigmentation or hypopigmentation. Patients should be reassured that with appropriate sun protection, this too will fade and resolve in time.

Simple emollients are beneficial to relieve the dryness and irritation. If itching is present, a mild topical corticosteroid or an oral antihistamine may be prescribed. Triamcinolone acetonide 0.1% is often the topical treatment of choice and can be applied once or twice a day as needed for itching. Such oral antihistamines as cetirizine (Zyrtec), fexofenadine (Allegra) and diphenhydramine (Benadryl) can also provide relief of pruritus.

Some clinical studies have suggested that oral erythromycin6 administered for two weeks or oral acyclovir7 started at the onset of the eruption may expedite resolution of the rash. In addition, narrow-band UVB phototherapy has been suggested for persisting or highly bothersome cases of PR. Relatively few patients experience relapses or recurrences.

The patient in this case was educated regarding the benign nature of the rash and the natural course of spontaneous resolution within a few weeks. She was given a prescription for a medium-potency topical steroid to be used once or twice a day as needed for itching. The patient reported that the rash resolved approximately seven weeks after it started without any evidence of scarring.

Esther Stern, NP-C, is a family nurse practitioner at Advanced Dermatology & Skin Surgery, P.C., in Lakewood, N.J.


1. Chuh AA, Lee A, Molinari N. “Case clustering in pityriasis rosea: a multicenter epidemiologic study in primary care settings in Hong Kong.” Arch Dermatol. 2003;139:489-493.

2. Kosuge H, Tanaka-Taya K, Miyoshi H et al. “Epidemiological study of human herpesvirus-6 and human herpesvirus-7 in pityriasis rosea.” Br J Dermatol. 2000;143:795-798.

3. Kay MH, Rapini RP, Fritz KA. “Oral lesions in pityriasis rosea.” Arch Dermatol. 1985;121:1449-1451.

4. Ahmed I, Charles-Holmes R. “Localized pityriasis rosea.” Clin Exp Dermatol. 2000;25:624-626.

5. Panizzon R, Bloch PH. “Histopathology of pityriasis rosea Gibert. Qualitative and quantitative light-microscopic study of 62 biopsies of 40 patients.” Dermatologica. 1982;165:551-558.

6. Sharma PK, Yadav TP, Gautam RK et al. “Erythromycin in pityriasis rosea: A double-blind, placebo-controlled clinical trial.” J Am Acad Dermatol. 2000;42(2 Pt 1):241-244.

7. Drago F, Vecchio F, Rebora A. “Use of high-dose acyclovir in pityriasis rosea.” J Am Acad Dermatol. 2006;54:82-85.

All electronic documents accessed June 7, 2012.

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