Autoimmune > Microscopic polyangiitis

Microscopic Polyangiitis:


Microscopic polyangiitis (MP) is an ANCA-associated nongranulomatous necrotizing small vessel systemic vasculitis that lacks an eosinophilic component [1,2,3]. It is the most common cause of pulmonary-renal syndrome (diffuse pulmonary hemorrhage and glomerulonephritis) [1,2,3]. The disorder is primarily renal, and less commonly pulmonary [1]. The median age of onset is 50 years [2]. There is typically a long prodromal phase of symptoms such as fever and weight loss [2,3]. More than 90% of patients then have a rapidly progressive glomerulonephritis at presentation [1]. Pulmonary involvement occurs in approximately 25-50% of patients [2]. Diffuse pulmonary hemorrhage occurs in 10-30% of patients and is commonly present at time of presentation [1].  Pulmonary symptoms include hemoptysis and shortness of breath [1]. Other manifestations include skin lesions, peripheral neuritis, and GI hemorrhage [1]. The musculoskeletal system, heart, and eyes can also be involved [3]. On lab analysis 40-80% of patients are p-ANCA positive [anti-MPO] (sensitivity 35-70%) [1,2].

Histolgically, a necrotizing vasculitis most often affects venules, arterioles, and capillaries [3]. Pulmonary capillaritis manifests as interstitial neutrophilic infiltration and causes necrosis of the alveolar and capillary walls which results in diffuse alveolar hemorrhage [3].


CXR: The radiologic features reflect DAH with patchy or bilateral diffuse airspace consolidation and GGO [1]. DAH may be more prominent in the perihilar areas and in the middle and lower lung zones (sparing the apices and CP angles) [2].

CT: The most common CT features are bilateral GGO and consolidation- most commonly involving the lungs diffusely or perihilar areas [2,3]. A ground-glass halo around the consolidations indicates there hemorrhagic nature [3]. Sooth interlobular septal thickening becomes superimposed on areas of GGO within 2-3 days producing a "crazy-paving" appearance [2,3]. Pleural effusion is uncommon [2], but other authors suggest that pleural effusion can be seen and are most likely related to underlying renal failure [3].



(1) Radiographics 2010; Castaner E, et al. When to suspect pulmonary vasculitis: radiologic and clinical clues. 30: 33-53

(2) Radiology 2010; Chung MO, et al. Imaging of pulmonary vasculitis. 255: 322-341

(3) AJR 2013; Nemec SF, et al. Noninfectious inflammatory lung disease: imaging considerations and clues to differential diagnosis. 201: 278-294

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