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Skin infections

Exanthems

Objectives

  • Be able to identify common and important exanthems.

Key points

  • An exanthem is a widespread erythematous rash that is accompanied by systemic symptoms such as fever, headache and malaise.
  • Exanthems are caused by viral infections (mostly affecting children), bacterial toxins and drug eruptions.
  • Chickenpox (herpes varicella/zoster) is characterised by mild systemic symptoms and truncal papules / vesicles / pustules that crust over and may leave scars. In adults may cause pneumonia. May be complicated by streptococcal cellulitis.
  • Measles is a febrile illness with cough, coryza, conjunctivitis, Koplik spots (oral papules). The rash commences on the cheeks and spreads to trunk and limbs as widespread "morbilliform" erythema (5-10mm macules). Prevented by vaccination.
  • Rubella is a mild febrile illness associated with lymphadenopathy and a pale pink erythema. Congenital rubella infection results in major birth deformities hence females at least should be vaccinated in adolescence.
  • Roseola infantum or erythema subitum (due to herpes virus 6, which may also be asymptomatic) presents as a mild toxic erythema in young babies. It arises on the third day of illness as high fever settles.
  • Fifth disease or erythema infectiosum (parvovirus B19) appears in epidemics during childhood. It is characterised by burning red swollen “slapped” cheeks followed by evanescent lacy-pattern erythema on the limbs. May cause arthralgia in adults and rarely aplastic crises. Congenital infection may result in fetal hydrops, anaemia and intrauterine death.
  • Kawasaki disease, or mucocutaneous lymph node syndrome, is uncommon in New Zealand. In some cases it is associated with known infections such as streptococcal disease. The exanthem predominantly affects perioral and genital areas but may be diffuse, with swollen fingers and toes that later peel. The child is unwell with fever, lymphadenopathy, conjunctivitis and strawberry tongue. Aspirin/ immune globulin may prevent cardiac aneurysms.
  • Scarlet fever is due to specific toxins released by Streptococcus pyogenes. It presents as a febrile illness with tonsillitis, strawberry tongue and "scarlatiniform" erythema (2-3mm macules) followed by generalised peeling a week or so later.
  • Purpura on distal extremities in a sick child or adult with fever and headache is indicative of meningococcal disease. Treatment with penicillin and admission to hospital should be immediately arranged, whether or not there are other symptoms such as vomiting, meningism and confusion.
  • Toxic shock syndrome and toxic shock-like syndrome are due to staphylococcal and streptococcal toxins respectively. Fever and hypotension (shock) are accompanied by a diffuse erythematous rash and swollen fingers and toes (which later peel profusely). The cause may be a retained tampon or an abscess, which should be drained. Admit for supportive care and treat with intravenous anti-staphylococcal antibiotics.
  • Staphylococcal scalded skin syndrome results in widespread erythema and superficial blistering/peeling in infants. In older people may complicate chronic renal failure.
  • Pityriasis rosea is characterised by herald patch a few days prior to the eruption of predominantly truncal oval scaly plaques. These persist for 6 to 12 weeks. Some cases are due to herpes virus 7, but the cause is unknown in the majority.

Introduction

An exanthem is the name given to a widespread erythematous rash that is usually accompanied by systemic symptoms such as fever, malaise and headache. The primary lesion may be a macule, papule, vesicle or patch. Exanthems are usually caused by an infectious condition such as a virus, and represent either a reaction to a toxin produced by the organism, damage to the skin by the organism, or an immune response. Exanthems may also be due to a drug (especially antibiotics).

Exanthems during childhood are usually associated with the viral skin infections listed below.

Less common bacterial or viral infectious conditions causing skin signs include:

Most common childhood viral exanthems have distinct patterns of rashes and prodromal (pre-rash) symptoms. If the patient shows classical features of the viral infection then diagnosis is usually clear-cut. However, when there are no characteristic lesions and/or distinctive prodromal signs and symptoms, diagnosis of a specific cause is made more difficult. In addition, some children may only be ill for a very short time and a specific diagnosis may not be possible. It becomes important to make a definitive diagnosis if the child has been exposed to pregnant women or immunocompromised patients.

Diagnosis of other causes of exanthems is important as some of these conditions can become life-threatening if not treated urgently with appropriate medications, e.g. meningococcal disease, Kawasaki's disease.

For most patients with non-specific exanthems no treatment is required as the condition is usually short-lived and resolves spontaneously. If necessary, symptomatic treatment with paracetamol to reduce fever and/or with topical/oral antihistamines or preparations such as calamine lotion to relieve itch may be used.