Henoch-Schonlein purpura

Henoch-Schonlein purpura (HSP) is a type of non thrombocytopaenic immune mediated small vessel acute leucocytoclastic vasculitis. 

It tends to occur in the paediatric population (peak incidence 3 - 10 years) ³.

In order to differentiate from other types of vasculitides, the four commonly adopted diagnostic criteria by the american college of rheumatology are

• age of onset less than 20 years ( although some case series show disease involvement in older individuals)
• palpable skin purpura
• gastrointestinal bleeding
• biopsy showing  granulocytes around small arterio / venular walls.

Pathology

There is deposition of IgA immune complexes in small vessels

Distribution

Commonest organ systems which get involved are

• skin : 95 - 100 % : usually the first organ to get involved
• gastrointestinal tract : 50 - 75 % 
• joints : ~ 80 % ⁶
• kidneys 

Rare sites

• central nervous system ^5,7

Radiographic features

Gastrointestinal tract

Plain film

May show evidence of bowel wall thickening due to haemorrhage and / or evidence of bowel obstruction. plain film features are however non specific.  

Fluoroscopy : Small bowel follow though

May show evidence of  seperation of bowel loops, "thumb printing" and / or mucosal thickening 

CT 

May show multifocal bowel thickening, lymphadenopathy, mesenteric oedema and vascular engorgement. Although non specific may aid to the diagnosis of HSP in a young patient with acute gastrointestinal illness along with other (e.g. cutaneous features of HSP).

Prognosis

The disease often tends to be self limiting in most instances. 

Complications

Gastrointestinal tract

• small bowel intussusception
• small bowel obstruction
• small bowel infarction : 3 - 5 % ³ 
• bowel perforation

Renal

• renal failure

Etymology

Named after Eduard Heinrich Henoch : German pediatrician (1820 - 1910) ⁸ and Johann Lukas Schönlein : German physician (1793 - 1864) 

Differential diagnosis

On a CT / contrast study for the bowel consider

• inflammatory bowel disease (e.g. Crohn's disease)
• small bowel lymphoma
• ischaemic colitis