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QuestionChoice
Acute chest syndrome is a severe complication of sickle cell disease. It is caused by infarction of lung tissue as the sickled red blood cells occlude pulmonary vasculature. Typical presenting features include fever, cough, chest pain and shortness of breath. Their physical examination can be normal, or findings such as crepitations and reduced air entry on auscultation can be found. Anaemia and thrombocytopenia are also typical features. However, this would not explain the white cell count. The main differentiating biochemical feature is this patient's reticulocyte count. There will be a high reticulocyte count in acute chest syndrome as the body is trying to produce red blood cells to replace those lost in haemolysis. A low reticulocyte count indicates a failure of bone marrow. This makes aplastic crisis secondary to parvovirus B19 infection the most likely diagnosis
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Acute chest syndrome
QuestionChoice
Autoimmune haemolytic anaemia can present as a normocytic (or macrocytic) anaemia. However, this would not typically cause a low white cell or platelet count. Reticulocyte count is also characteristically high in autoimmune haemolytic anaemia as the body is trying to compensate and produce more red blood cells
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b
Autoimmune haemolytic anaemia
QuestionChoice
B12 deficiency anaemia presents with a macrocytic anaemia. In this case, this patient presented with a normocytic anaemia. This would also not explain the leukopenia and thrombocytopenia in this patient's blood tests. Of note, a combination of iron deficiency anaemia and megaloblastic anaemia can present as a normocytic anaemia, as the macrocytic and microcytic cells create a normocytic mean cell volume. This could be further investigated with a red cell distribution width. However, this is more common in conditions like coeliac disease. Given this patient's clear history of sickle cell disease and the presence of leukopenia, thrombocytopenia and a low reticulocyte count, aplastic crisis secondary to parvovirus B19 infection is the most likely diagnosis
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B12 deficiency
QuestionChoice
An aplastic crisis is a sickle cell crisis associated with the bone marrow not producing any cells. The most common cause is infection with parvovirus B19. Parvovirus B19 causes fifth's disease (also known as slapped cheek syndrome or erythema infectiosum), usually a benign, self-resolving childhood illness. In children with sickle cell disease, their red blood cells have a much shorter survivability meaning that cessation of new blood cell production, which can be associated with parvovirus B19 infection, can lead to pancytopenia over days. Features that point to this diagnosis include a history of sickle cell disease, acute onset of pallor and breathlessness over a few days, normal auscultation and pancytopenia with normocytic anaemia. Reticulocyte count is another key feature in this question. In haemolytic anaemias, reticulocyte count is high as the body tries to make red blood cells to compensate for the haemolysis. Low reticulocyte count suggests red cell production failure, making aplastic crisis secondary to parvovirus B19 infection the most likely diagnosis. Of note, although chest auscultation is often normal in anaemia, a flow murmur may be heard in severe anaemia
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Parvovirus B19 infection
QuestionChoice
Acute lymphoblastic leukaemia (ALL) can also present with pancytopenia, although it typically affects children under 6. Lymphadenopathy and hepatosplenomegaly are characteristic features of leukaemia, although their absence does not rule out leukaemia. Although patients with ALL can present with low haemoglobin and low platelets, the white cell count is characteristically high. This is because the bone marrow produces an excessive amount of lymphoblasts (lymphocyte precursors), which reduces the proportion of bone marrow able to produce other cells (leading to thrombocytopenia and anaemia). The low white cell count makes acute lymphoblastic leukaemia unlikely in this patient
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Acute lymphoblastic leukaemia
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# Summary
 

Fifth disease, also known as " slapped cheek syndrome" or erythema infectiosum, is a viral illness caused by Parvovirus B19. It typically presents in children with a prodrome of fever, coryza, and diarrhoea, followed by a distinctive 'lace-like' rash across the body and bright red cheeks. Diagnosis is typically clinical, with management being largely supportive. Complications can include red cell aplasia, severe anaemia in vulnerable populations, and severe foetal anaemia in pregnant women, which can lead to hydrops foetalis and miscarriage. 
 

# Definition
 

Fifth disease, or erythema infectiosum, is a viral illness caused by Parvovirus B19 most commonly occurring in children.
 

# Epidemiology
 

This illness is widespread and can occur in outbreaks, particularly in school settings. It is most common in late winter and early spring. 

It is most common in children aged 6-10 years but can affect individuals of any age. 50% of children aged 15 years and almost 90% of older people have evidence of previous parvovirus B19 infection. 
 

# Aetiology
 

Fifth disease is caused by Parvovirus B19, a virus that specifically targets erythroid progenitor cells, hence its particular association with certain haematological complications. It is spread through droplet transmission with an incubation period of 14-21 days.  
 

# Signs and Symptoms
 

- Prodrome of fever, coryza, abdominal pain, headache
- This is followed 1-2 weeks later by 
     - Characteristic bright red rash on the cheeks, giving rise to the name " slapped cheek syndrome"
     -  A few days later - a diffuse 'lace-like' rash develops across the body, this may last 1-3 weeks 

Many people are asymptomatic with the virus. 

[lightgallery]
 

# Differential Diagnosis
 

 - **Rubella**: presents with a similar rash, but also includes lymphadenopathy and conjunctivitis
 - **Scarlet fever**: presents with a similar rash, but also includes a sore throat and a 'strawberry' tongue
 - **Roseola infantum**: presents with a high fever followed by a rash, but the rash is typically non-pruritic and pink in colour
 

# Investigations
 

Diagnoses are typically made clinically based on presentation. In atypical cases or when complications are suspected, serological testing for Parvovirus B19 can be performed. FBC may reveal low reticulocyte count.
 

# Management
 

- Management is largely supportive, including rest, hydration, and over-the-counter remedies for fever and itching
- In cases with severe complications such as aplastic crisis, hospitalisation and transfusions may be required.

The rash means that the child is no longer infectious, so is able to attend school and nursery. The school, however, should be notified such that high-risk groups who have been in contact with the child should seek attention (i.e. pregnant women or immunocompromised). 
 

# Complications
 

 - Red cell aplasia: Parvovirus infection reduces erythropoiesis, which can precipitate severe anaemia and aplastic crisis in vulnerable groups such as those with conditions like sickle cell anaemia and hereditary spherocytosis.
 - Severe foetal anaemia: Infection in the first half of pregnancy can cause severe foetal anaemia that can precipitate hydrops foetalis and subsequent miscarriage.
 - Cardiomyopathy
 - Neurologic complications:
      - Encephalitis, meningitis, stroke, and peripheral neuropathy can all occur due to parvovirus B19 infection

 
#  Prognosis 

Slapped cheek syndrome is typically a mild, self-limiting viral syndrome but thereafter the individual is immune lifelong. 

 
#  NICE Guidelines 
 
 [NICE Guidelines Parvovirus B19 infection](https://cks.nice.org.uk/topics/parvovirus-b19-infection/) 
 

# References
 
 [NHS Information on Slapped cheek syndrome](https://www.nhs.uk/conditions/slapped-cheek-syndrome/) 

 [Information on Parvovirus B19](https://www.arthritis.org/diseases/fifth-disease)
 
 [Patient Info Slapped cheek disease](https://patient.info/childrens-health/slapped-cheek-disease-leaflet)
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Parvovirus B19
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Haematology
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An 8-year-old boy presents to the emergency department with shortness of breath, gradually getting worse over the last few days. He has a history of sickle cell disease. On examination, he has conjunctival pallor, normal auscultation of the chest and no hepatosplenomegaly. His blood results are shown below:


||||
|--------------|:-------:|---------------|
|Haemoglobin|72    g/L|(M) 130 - 170, (F) 115 - 155|
|White Cell Count|1.2x10<sup>9</sup>/L|3.0 - 10.0|
|Platelets|43x10<sup>9</sup>/L|150 - 400|
|Mean Cell Volume (MCV)|88 fL|80 - 96|
|Reticulocytes|1x10<sup>9</sup>/L|25 - 100|


Which of the following is the most likely cause of this patient's blood results?
a