Monday, November 12, 2012

The Vasculitides: Microscopic Polyangiitis (MPA)

There are no pictures in this post... because there is no classic radiographic appearance of microscopic polyangiitis (MPA).  Just as its generic name implies, it has a nonspecific presentation...

An ANCA+ small vessel vasculitis in the group of Wegener's granulomatosis and perhaps Churg-Strauss syndrome, microscopic polyangiitis is being frequently "isolated" out from prior studies in which it was lumped in with other, more well-recognized vasculitides... for instance, it's been recognized that in some of the published series investigating polyarteritis nodosa, some of the cases were actually microscopic polyangiitis. They have many of the same clinical symptoms.

So how could you make a prospective radiologic call of microscopic polyangiitis?  It would seem that you can't.

But you can choose not to suggest it when certain features are present.

1) As the name implies, it's a microscopic vasculitis, affecting capillaries, arterioles, and venules.  Findings of medium or large vessel vasculitis on angiography do not occur.

2) Polyarteritis nodosa never involves the lungs.  If you have findings suspicious for PAN, but with lung involvement (alveolar hemorrhage, diffuse alveolar damage), then microscopic polyangiitis is reasonable to put on the differential in its place.

3) Polyarteritis nodosa does not cause rapidly-progressive glomerulonephritis.

4) Microscopic polyangiitis does not cause renal aneurysms.

The age of presentation of MPA (avg. 50Y), is not significantly different than in other vasculitides.  The renal-pulmonary presentation is similar to Goodpasture's syndrome.  Occasionally, it can affect the GI tract, similar to other small vessel vasculitides, such as Henoch-Schonlein purpura.

1. "Vasculitis" Ball GV and Bridges SL. Oxford publishers (2002)
2. Ha HK, Lee SH, Rha SE. "Radiologic Features of Vasculitis Involving the Gastrointestinal Tract" RadioGraphics 2000; 20:779–794