A 26-year-old woman presented with a sudden onset of rashes over trunk

Man-ho Chung

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Clinical history:

A 26-year-old woman presented with a sudden onset of rashes over trunk. It began with a single enlarging patch of rash over her lower chest wall, 2 days later it spread to the front and back of the trunk. A few papules appeared over limbs as well. They were only mildly itchy. Prior to the onset of rash, she did not take any new medications or underwent vaccination. Except some nonspecific malaise, there were no other systemic symptoms. She was otherwise healthy with no significant family history of autoimmune disease.

What is the diagnosis?

Answer:
D. Pityriasis rosea

The clinical photos showed symmetrically distributed annular scaly erythematous papules and patches over the trunk. All lesions subsided around 7 weeks after the appearance of the first patch. Only low-potency topical steroids were used on symptomatic sites in this case. Laboratory results were unremarkable, including a negative Venereal disease research laboratory (VDRL) test, negative Anti-Nuclear Antibody (ANA) result and a negative fungal culture from skin scraping. The clinical course and characteristic appearances of the rash suggested the diagnosis of pityriasis rosea. Pityriasis rosea is a commonly encountered benign condition that occurs in healthy adolescents and young adults. The classical clinical course of pityriasis rosea begins with the development of a solitary “herald patch” on the trunk that enlarges over several days. Subsequently, multiple papular lesions and plaques erupt over the trunk and proximal limbs hours to days after that. These subsequent lesions are usually oval shaped with the long axis following the Langer cleavage lines, resembling a Christmas tree pattern over the back. It then follows by self-resolution around 6-8 weeks after the initial onset. The herald patch is usually a 2-4 cm large erythematous patch with an advancing margin and a trailing collarette of scale. The face, palms and soles are usually spared unless in atypical presentations. Moreover, vesicular, pustular and urticarial variants have been described. Eruptions of pityriasis rosea are often only mildly pruritic or even asymptomatic. The peak age of onset is between 10-35 years of age with a slight female predominance. The aetiology of pityriasis rosea is postulated to be viral related. Human herpesvirus 6, 7 are reported to be implicated in the pathogenesis. Features that support the viral aetiology include occasional prodromal symptoms, case clustering and rare recurrence of the disease. In addition, one should beware that pityriasis rosea-like eruption can be induced by various drugs and vaccines. Recently, it is uncommonly reported after COVID vaccinations. Pityriasis rosea belongs to the group of papulosquamous eruptions. Accordingly, the differential diagnosis should include other common papulosquamous disorders like discoid eczema, guttate psoriasis, tinea corporis, subacute cutaneous lupus erythematosus and erythema annulare centrifugum. The key to distinguish pityriasis rosea from other similar eruptions is the typical rash progression and self-limiting history. Together with the presence of a herald patch and the typical rash orientation, making the correct diagnosis is straightforward. Discoid eczema (or nummular eczema) can appear in all age groups. It is typically more pruritic than pityriasis rosea and often runs a chronic clinical course. Collarette scaling is absent. Lesions of guttate psoriasis usually contain thicker scale and do not follow a Christmas tree pattern. Tinea corporis can be excluded by performing a skin scraping for fungus. The leading edge with central clearance and the absence of trailing scale can help distinguish it from pityriasis rosea. Secondary syphilis is an important differential diagnosis, especially in sexually active patients. There are usually more systemic complaints including fever and lymphadenopathy. Palm and soles lesions are much more common. Therefore, enquiring for sexual history and testing for syphilis serology is required to exclude this similar cutaneous disorder. The diagnosis of pityriasis rosea is mainly clinical, and in atypical presentations may require skin biopsies to rule out other aforementioned skin disorders. Indeed, the pathological findings of pityriasis rosea are quite nonspecific and nondiagnostic. Hence, skin biopsies are not typically necessary. The treatment of pityriasis rosea is mainly supportive. Often the lesions are asymptomatic and thus do not require any medication. Counselling and reassurance are important parts of management. Timely follow-up to ensure resolution of the lesions should be offered. In case of an atypical disease course noted during follow-up, alternative diagnoses should be considered. For itchy lesions, emollients, low- to-medium-strength topical steroids and antihistamines can be used. In severe and symptomatic cases, phototherapy or a short course of systemic steroids may rarely be required. Other treatment options that were reported in the literature include 14 days of erythromycin 250mg four times per day or one week of acyclovir 800mg five times daily, both may lead to faster resolution of lesions.

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The slide and the question were prepared by:

Dr. Man-ho Chung, ^{MBBS (HK), MRCP (UK), FHKCP, FHKAM (Medicine)}

Associate Consultant,

Department of Medicine, Queen Mary Hospital, Hong Kong SAR