Viral Exanthems

A viral exanthem is a vascular response to hematogenous dissemination of virus to the skin. It appears as erythematous macules and papules. Numerous viruses can give rise to an exanthem, but common ones are measles (rubeola), German measles (rubella), herpesvirus 6 (roseola), parvovirus B19 (erythema infectiousom, "fifth" disease), and enteroviruses (e.g. ECHO and coxsackievirus). The appearance of the rash is not specific for a particular virus and correlation with other symptoms and history is required. They are, of course, common in childhood (except for those significantly reduced by vaccination, such as measles and rubella.)

With what can it be confused?

Viral exanthems may be confused with drug eruptions, toxic erythemas, and Rocky Mountain spotted fever (RMSF). Drug eruptions are usually more extensively confluent, more brightly red ("drug" red), and more pruritic than viral exanthems. Toxic erythemas have a "sand paper" texture and favor flexural folds. RMSF begins as macules and papules on the distal extremities, spreads centripetally, and becomes purpuric.

How is it diagnosed?

Viral exanthems are diagnosed clinically; laboratory investigation are usually not helpful, though antibody titers in convalescent versus acute serum samples can confirm the diagnoses. Viral exanthems are typically preceded by a prodrome of fever and other constitutional symptoms, such as malaise. Lymphadenopathy is sometimes present. A history of sick contacts may be elicited. Depending on the virus, the incubation period can vary from days to weeks. Some viral illnesses have specific features that aid in identification.

Measles is characterized by the classic "3 C's: cough, coryza (runny nose) and conjunctivitis. The rash of measles will often become confluent on the face and trunk, but remain discrete on the extremities. Rubella (German measles) will remain as discrete lesions, even on the face and trunk. Both measles and German measles start on the head and descend. Measles and rubella may both have mucous membrane involvement. Koplik's spots are small gray or white papules on an erythematous base on the buccal mucosa; it may be the first sign of infection. In rubella there may be red spots on the soft palate.

In roseola (exanthem subitum) the lesions are "rose" colored macules and papules distributed on the trunk and proximal extremities. It is the most common viral exanthem in children under the age of two. Erythematous macules may be observed on the palate prior to the exanthem. The fever, which may be quite high, usually subsides just prior to the rash erupting.

Erythema infectiousum, also known as "fifth' disease, occurs in school-age children. The affected child is classically described as having a "slapped cheeks" appearance that is followed by a reticulate (net-like) rash on the trunk and proximal extremities.

The rash associated with enteroviruses is variable. It is often rubella-like (i.e. erythematous macules and papules) but may also be purpuric or vesciular.

How is it treated?

There is no specific treatment for these viral illnesses, other than symptomatic relief. The measles, mumps, rubella (MMR) vaccine is highly effective in preventing these diseases.

What is the prognosis?

Resolution usually occurs over days to weeks, usually without complications. The most serious complication is encephalitis which can occur with measles and enterovirus infections. Secondary bacterial infections, especially pneumonia, can also complicate measles. Arthritis is a complication of both rubella and parvovirus B19 infection. Parvovirus B19 can also cause acute aplastic anemia in susceptible persons, especially those with sickle cell disease.

Rubella during the first trimester of pregnancy can result in congenital rubella syndrome in the newborn with devastating results.

Image links

DermnetNZ: Multiple images of viral exanthems