... but the source of the palpable purpura is a small-vessel vasculitis, and like other vasculitides, HSP is a multisystem disorder, affecting the joints, kidneys, and GI tract. The official 1990 ACR criteria are 2+/4 of:
1. Palpable purpura
2. Age younger than 20y at disease onset
3. Bowel angina
4. Biopsy showing granulocytes in the wall of arterioles or venules.
Like in microscopic polyangiitis (see yesterday's post) the glomerulonephritis from the small-vessel vasculitis is actually the most serious aspect of HSP, but it's not well-appreciated radiologically.
GI manifestations of HSP, however, can be picked up... and since it's estimated that 65-75% of people with HSP have GI symptoms (colicky abdominal pain, vomiting, bloody stools), the radiological findings in HSP are characteristic enough to help determine if a patient's acute abdomen is related to the vasculitis or if it has some other source.
One way to think about the GI involvement of HSP is that what it's doing to the skin... it's also doing to the bowel. The abdominal pain in HSP is related to visceral purpura leading to submucosal and mucosal extravasation of blood and edema, which can lead to ulceration of the bowel mucosa. this can occur anywhere from the duodenum to the colon, and can often be seen with endoscopy.
On fluoroscopy, these changes result in thickening of the bowel wall, with thickened folds, thumbprinting, separation of loops, and prolonged transit time. Infrequently (1-5%) the bowel wall thickening can act as a lead point for intussusception. This appearance is not specific for HSP, however, and in older patients, other more common diagnoses, such as Crohns disease or infection should be entertained. Lupus causing small artery vasculitis should also be entertained.
|CT correlation of the fluoroscopic findings. Free fluid in the paracolic gutters also noted.|
In addition to CT and fluoroscopy, ultrasound is also considered a viable option for detection of bowel wall thickening in HSP. Reported findings in addition to bowel wall thickening include reduced peristalsis, small bowel dilatation, and free fluid in the abdomen.
Although a small-vessel vasculitis, HSP is in a different category than Wegener's, Churg-Strauss, or Microscopic Polyangiitis. HSP's vasculitis is associated with IgA-dominant immune deposits in the walls of small vessels (a leukocytoclastic angiitis), and it is not ANCA positive like the others. HSP can be differentiated from systemic lupus eryhtematosus since HSP does not have ANA with +dsDNA Ab.
The majority of cases of HSP occur in children, with 50% of cases at 5y or younger and 75% at 10y or younger. The abdominal pain in HSP can actually precede the rash, so physical exam is not always the foolproof diagnosis for acute abdominal pain and HSP.
1. "Vasculitis" Ball GV and Bridges SL, ed. Oxford publishers. (2002).
2. Saulsbury FT. "Henoch-Schonlein Purpura" Current Opinion in Rheumatology 2010, 22:598–602
3. Ha HK, Lee SH, Rha SE. "Radiologic Features of Vasculitis Involving the Gastrointestinal Tract" RadioGraphics 2000; 20:779–794