29th January 2024

Background

Epidemiology 

Children are most often affected, but Henoch-Schönlein Purpura (HSP) can affect adults of all ages. Half the affected children are under the age of 5. Kidney involvement is more likely to be severe in older children and adults. It affects both sexes equally.

Aetiology

In two-thirds of cases, the disease follows an upper respiratory tract infection, with onset an average of 10 days after the start of symptoms. However, no single microorganism or environmental exposure has been confirmed to cause HSP. 

Streptococcus strains and Parainfluenza virus are the most commonly associated pathogens, and in children, Human Parvovirus B19 is a frequent viral trigger.

Pathophysiology 

IgA antibodies act to protect the lining of the airway, throat and gut, hence why HSP is triggered by infections in those organs. IgA binds to and cross-reacts with the endothelial cells following the activation of complement factors. This damages the endothelium. Inflammation of the small blood vessels causes bleeding into the skin and, therefore, produces the typical purpuric rash, primarily seen on the lower limbs.