An exanthem is an eruptive, widespread rash. A viral exanthem is of course an exanthem that accompanies a viral infection.
Originally, there were 6 viral exanthems which were named based on their numerical order (first disease → sixth disease). They have since been renamed:
Scarlet fever is a reaction to exotoxins produced by Group A haemolytic streptococci (usually streptococcus pyogenes). It is most common in children aged 2-6 years old with peak incidence at 4 years old.
It is transmitted by respiratory droplets through inhalation or ingestion or by direct contact.
😷 Presentation
It has an incubation period of 2-4 days and typically presents with:
- Fever
- Malaise
- Headache
- Nausea and vomiting
- Strawberry tongue - a white coating appears on the tongue. This peels, leaving the tongue red, swollen and covered in little bumps that give the appearance of a strawberry.
- Rash
- Red-pink, blotchy, macular rash
- Sandpaper texture
- Flushed cheeks
- Fine punctuate erythema - erythema in minute points. They generally appear on the torso first and spares the palms and soles.
- Circumoral pallor - the area around the mouth appears pale.
- Desquamination - shedding of the skin occurs later in the course (especially around the fingers and toes).
🔍 Investigations
A throat swab is normally taken but antibiotic treatment should be started immediately based on the clinical diagnosis.
🧰 Management
- Notify local health protection team
- 🥇 Oral penicillin V - for 10 days.
- 🥇 Azithromycin - for patients with a penicillin allergy.
- Children can return to school 24 hours after starting antibiotics.
🚨 Complications
- Otitis media - this is the most common complication.
- Rheumatic fever - usually 20 days after infection.
- Acute glomerulonephritis - around 10 days after infection.
- Bacteraemia, meningitis and necrotising fasciitis - rare but life-threatening illnesses that may occur if the infection spreads.
Duke’s disease is not used in clinical practice and has been forgotten for the most part.
When it was first described, there was controversy around its existence or whether doctors were misdiagnosing a different illness. Since viral and bacterial testing has become possible, no organism has been found to explain the so called “fourth disease”. It has subsequently been removed and there are technically only 5 viral exanthems
Parvovirus B19, also known as slapped cheek syndrome or erythema infectiosum is the fifth viral exanthem. It is self-limiting and the rash and symptoms dissipate after 1-2 weeks.
It is transmitted by respiratory droplets. It is infectious prior to rash formation, however, once the rash forms they are no longer infectious (and do not need to be excluded from school as a result).
😷 Presentation
There is a prodrome of mild fever, coryzal symptoms, malaise and lethargy. However, it is often so mild and not noticed.
- Rash - the rash appears quite suddenly after 2-5 days as a diffuse, bright-red rash on both cheeks (i.e. slapped cheeks).
- After a few days a reticular (lace pattern) mildly erythematous rash appears on the trunk and limbs. It may be raised and itchy.
- Similar to scarlet fever, it spares palms and toes.
The rash peaks after a week and then fades. However, the bright red cheeks reappears for months after when exposed to a warm bath, sunlight, heat or fever.
🧰 Management
- It is self-limiting in healthy individuals and supportive management is all that is required.
- If a women is exposed in early pregnancy (<20 weeks) she should speak to whoever is providing antenatal care as we need to check maternal IgM and IgG and treat with intra-uterine blood transfusions.
- This is because the virus is able to cross the placenta and cause severe anaemia due to viral suppression of erythropoiesis → heart failure (secondary to the severe anaemia) → hydrops fetalis.
🚨 Complications
- Aplastic anaemia
- Encephalitis or meningitis
- Pregnancy complications - as described above.
In high-risk groups such as pregnant women, Immunocompromised patients, and patients with haematological conditions we should do serological testing and check FBC and reticulocyte count to exclude haemolysis.
Roseola infantum, also known as simply roseola or exanthem subitum, is the 6th exanthem. It is caused by human herpesvirus 6 (HHV-6) and sometimes by HHV-7.
It has an incubation period of 5-15 days and typically affects children aged 6 months - 2 years.
😷 Presentation
It has a typical pattern:
- Fever - for 2-7 days. The fever is quite a high fever, reaching >39.5ºC.
- Diffuse erythematous mild macular rash - that appears across arms, legs, trunk and face as the fever subsides. It is not itchy.
Other common features include:
- Diarrhoea
- Cough
- Abdominal pain
- Nagayama’s spots - these are red papules on the soft palate and uvula.
- Coryzal symptoms
- Tympanic membrane inflammation
🔍 Investigations
Clinical diagnosis
🧰 Management
It is self-limiting and supportive management is all that is required once again. Children need to be kept out of nursery until they are well enough to attend.
🚨 Complications
- Febrile convulsions
Immunocompromised patients may be at risk to myocarditis, thrombocytopenia, Guillan-Barre syndrome, but these are rare.