28 一位9歲女童於雙側臉頰出現紅斑，四肢伸展側有網狀紅斑，並無發燒與呼吸道症狀。下列那一項是最可能的診斷？

Drug allergy Erythema infectiosum Rubella Scarlet fever

ans Erythema infectiosum

Background

Erythema infectiosum (fifth disease) is a common childhood exanthem caused by human parvovirus B19 (PV-B19), an erythrovirus, in which a classic 3-phased cutaneous eruption follows a rarely noticed prodrome.¹

Pathophysiology

The development of erythema infectiosum (fifth disease) in children is a normal response to infection by PV-B19. Acute infection in a host who is immunocompetent leads to a Th-1–mediated cellular immune response, with the production of specific immunoglobulin M (IgM) antibodies and subsequent formation of immune complexes. Clinical signs and symptoms of erythema infectiosum (fifth disease) probably result from the deposition of the immune complexes in the skin and joints of individuals with this condition and not from the circulating virus.