Fifth Disease

The parents of a 2-year-old sought treatment for a rash on their son's face. The child had had a low-grade fever for 3 days before the rash erupted. An intermittent lace-like rash was beginning to develop on the extremities. The patient was otherwise asymptomatic.

The differential diagnosis included common child exanthems, such as scarlet fever, measles, and rubella; drug reaction and cellulitis were considered as well.

Dr Ahmad Hakemi of Central Michigan University, Mount Pleasant, Mich, diagnosed fifth disease, or erythema infectiosum. The patient had no history of drug reactions and showed no signs of cellulitis. The mild fever, absence of sore throat, and the nature and distribution of the eruption ruled out scarlet fever, measles, and rubella.

Fifth disease is caused by parvovirus B19, a single-stranded DNA virus. Children are frequently exposed to the disease through contact with infected friends and siblings. Typically, confluent plaques develop on the face, giving the patient a “slapped-cheek” appearance. A lace-like pattern of macules and papules also arises on the trunk and extremities.

The incubation period is between 4 and 14 days; the illness usually lasts from 5 to 10 days. The often pruritic eruption may come and go for up to 5 weeks; heat and sunlight are among the factors that can incite exacerbations.

Erythema infectiosum is self-limited; no treatment is necessary. Arthritis, the most common complication, occurs in fewer than 10% of children. Pregnant women who are exposed to the disease are at risk for transplacental transmission of the virus, which may result in stillbirth or hydrops fetalis.