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Emergency And Acute Medicine – Pityriasis Rosea
Pityriasis rosea is a self-limited inflammatory skin eruption of unknown origin that primarily affects children and young adults. The condition often begins with a single lesion known as a herald patch, which is an ovoid, erythematous, slightly raised plaque usually located on the trunk or proximal extremities. Within 7–14 days, a secondary eruption develops, consisting of multiple smaller, salmon-colored, elliptic papules with fine scaling. These lesions typically align along Langer lines on the trunk in a symmetric “Christmas tree” distribution. Nearly 80% of cases resolve spontaneously within 1–2 months.
The exact cause is unknown, although weak evidence suggests a viral association, particularly with human herpesvirus types 6 and 7. Several medications have been linked to pityriasis-like eruptions, including barbiturates, captopril, clonidine, gold, isotretinoin, metronidazole, bismuth, interferon, imatinib (Gleevec), and the hepatitis B vaccine. There are weak associations with eczema, asthma, and underlying malignancies.
Many patients report mild prodromal symptoms in the days preceding the rash, including malaise, gastrointestinal upset, or upper respiratory symptoms. On examination, the herald patch is typically 2–10 cm in diameter and seen in 50–90% of cases. The secondary eruption follows, appearing symmetrically along cleavage lines, predominantly on the trunk and proximal extremities. Pruritus is common and may vary in severity. Inverse pityriasis rosea, characterized by lesions on the face and distal extremities with minimal trunk involvement, is more frequently observed in children. Rare pediatric cases may include oral lesions such as punctate hemorrhages or ulcerations.
Diagnosis is clinical and based on characteristic history and physical findings. No routine laboratory testing is required. However, when the herald patch is absent or the presentation is atypical, alternative diagnoses must be considered. Secondary syphilis can mimic the rash and should prompt testing with a rapid plasma reagin (RPR) in patients with risk factors. A potassium hydroxide (KOH) preparation may help distinguish tinea corporis or tinea versicolor.
The differential diagnosis for the herald patch includes nummular eczema and tinea corporis. The secondary eruption may resemble secondary syphilis, drug eruption, guttate psoriasis, lichen planus, seborrheic dermatitis, scabies, dermatomyositis, cutaneous lymphoma, lupus, Kaposi sarcoma, or occult malignancy. Toxic appearance or mucous membrane involvement should prompt reconsideration of the diagnosis.
No stabilization is required in the emergency setting. Pityriasis rosea is self-limiting, and treatment is directed toward symptomatic relief, particularly for pruritus. Topical corticosteroids such as hydrocortisone 1% cream applied three times daily and oral antihistamines such as diphenhydramine may provide relief. In more severe cases, short courses of oral prednisone may be used. Erythromycin has also been reported to reduce symptom duration in some patients.
Hospital admission is not required. Patients with a clear diagnosis may be discharged with reassurance that the condition is benign and typically resolves within 1–2 months. Dermatology referral may be considered for severe, persistent, or atypical cases, especially if pruritus is refractory.
Pityriasis rosea most commonly affects the trunk and proximal extremities. Involvement of mucous membranes, distal extremities, or a toxic clinical appearance should prompt evaluation for alternative diagnoses.
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