Acute polyarthritis. Fifth disease passed from child to adult.

Physicians are familiar with the "slapped cheek" rash seen in childhood cases of erythema infectiosum. Less well known is that infection with its pathogen, parvovirus B19, often becomes manifest in adults as acute viral arthropathy. In evaluation of suspected cases, a complete blood cell count and blood chemistry profile are useful additions to thorough history taking and physical examination. Differential diagnosis includes Lyme disease, other viral infections, acute rheumatoid arthritis, systemic lupus erythematosus, and psoriatic arthritis. Treatment is symptomatic with nonsteroidal anti-inflammatory drugs.