Pityriasis Rosea

For 3 weeks, a 3-year-old African American boy had a mildly pruritic rash on his buttocks, lower extremities, upper thighs, and soles. The patient was initially seen at an urgent care center, where he was given amoxicillin for suspected scarlet fever. A week later, he presented to the emergency department and was treated with griseofulvin for tinea corporis. A skin culture did not grow fungus.

The child's mother recalled that the rash started as a single patch on his lower back and that the child had an upper respiratory tract infection 4 weeks earlier.

The rash consisted of annular hyperpigmented plaques of 0.5 to 3 cm with dusky centers and whitish borders with scale. There was no mucosal membrane or scalp involvement. The rest of the examination findings were unremarkable. Pityriasis rosea was diagnosed.

Pityriasis rosea was first described by Gilbert in 1860 as pink scale. There may be several causative agents. A causal association between pityriasis rosea and active human herpesvirus (HHV) 7 and HHV6 has been suggested but not corroborated.¹ Pityriasis rosea is more common in the fall and spring. Half of all cases occur in patients younger than 20 years; females are affected more than males. An upper respiratory tract infection precedes the illness in up to 68% of cases.² The disease may pre- sent initially with mild prodromal symptoms, such as fatigue, headache, nausea, anorexia, chills, and arthralgia. Lymphadenopathy may occur before the onset of the rash.

Pityriasis rosea usually starts with a herald patch--which is typically the largest lesion and is commonly mistaken for tinea corporis. This is followed within 1 to 2 weeks by a papulosquamous plaque-like rash that lasts for about 6 to 12 weeks. In children, especially African American children,³ the lesions may be generalized or atypical in morphology and distribution, unlike the classic ovoid lesions in a Christmas tree pattern seen on the trunk of adults.

Treatment is unnecessary, but topical corticosteroids or oral antihistamines may be used for pruritus. Moisturizers may also be helpful. In one study, erythromycin used for 2 weeks resulted in complete resolution of the rash in 73% of patients, while the resolution rate was 0% in the placebo group.² Azithromycin did not provide the same efficacy.⁴ Another study concluded that high-dose acyclo- vir may be effective if started within the first week of the rash when HHV replicative activity is very high; however, this study relied solely on observation and counting of lesions to determine resolution.⁵

This patient was given diphenhydramine (5 mg/kg/d PO divided q6h) to relieve his itching. At follow-up 6 weeks later, the rash had completely resolved. *