Macular/maculopapular rashes

The macular/maculopapular rashes are most common in childhood and are not true infections of the skin. Rather they are exanthems (Fig. 3. 19.2), the primary infection occurring elsewhere with the rash as a secondary, probably immune-mediated, phenomenon. The virus cannot be easily, if at all, isolated from the rash. An enanthem (Fig. 3. 19.3), a rash on a mucous membrane, may also be detectable early in the illness; in measles these are called Koplik’s spots and manifest as white flecks on the buccal mucosa. Transmission is by the respiratory route, with upper respiratory tract symptoms being common, if transient.

Fig. 3.19.2 Viral exanthema: chickenpox.

Fig. 3.19.3 Viral enanthem: chickenpox.

Measles, a paramyxovirus, can cause a severe infection with constitutional symptoms and marked upper respiratory tract symptoms. It may be complicated by secondary bacterial pneumonia, typically from Staphylococcus aureus. It may also be complicated by neurological disease: acute ‘postinfectious’ measles encephalitis, which is immune mediated; subacute encephalitis, which can occur in immunocompromised patients; and, rarely, subacute sclerosing panencephalitis, occurring 5–10 years after primary infection. In children, particularly those with protein malnutrition, measles remains a common cause of death in the developing world.

Rubella classically manifests as a rash that starts on the face then spreads to the trunk with lymphadenopathy. It may be complicated by encephalitis, haematological deficiencies and an arthritis that affects small and medium-sized joints. The most serious manifestation, however, occurs if a pregnant woman is infected: the congenital rubella syndrome causes neural, cardiac, bone and other abnormalities in the fetus.

Other common causes of a maculopapular rash are parvovirus B19, which results in erythema infectiosum and human herpesvirus 6 (HHV6), which is associated with roseola infantum. Erythema infectiosum is commonly known as ‘slapped cheek syndome’ as the facial rash has that appearance. It is often complicated by a painful arthropathy in adults and may precipitate fetal loss in second trimester pregnancy and aplastic crises in those with haemolytic anaemia. Roseola infantum classically is preceded by 3–5 days of fever, which then leads to a rash on the trunk that spreads centrifugally.