Polyarteritis Nodosa
Posted by Alex
Definition
Classic polyarteritis nodosa (PAN) is a multisystem, necrotizing vasculitis of small and medium-sized muscular arteries in which involvement of the renal and visceral arteries is characteristic. PAN does not involve pulmonary arteries, although bronchial vessels may be involved; granulomas, significant eosinophilia, and an allergic diathesis are not part of the classic syndrome. The term microscopic polyangiitis (microscopic polyarteritis) discribes the necrotizing vasculitis with few or no immune complexes (pauci-immune) affecting small vessels (capillaries, venules, or arterioles). Since necrotizing arteritis involving small and medium-sized arteries may also be present, it shares features with classic PAN except that glomerulonephritis is very common in microscopic polyangiitis, and pulmonary capillaritis often occurs.
Incidence And Prevalence
Pan is an uncommon disorder. The mean age at onset in reports of PAN is 48 years, and the male-to-female ratio is 1.6:1.
Pathophysiology And Pathogenesis
The vascular lesion in classic PAN is a necrotizing inflammation of small and medium-sized muscular arteries. The lesions are segmental and tend to involve bifurcations and branchings of arteries. They may spread circumferentially to involve adjacent veins. However, involvement of venules is not seen in classic PAN and, if present, suggests microscopic polyangiitis or the polyangiitis overlap syndrome (see below). In the acute stages of disease, polymorphonuclear neutrophils infiltrate all layers of the vessel wall and perivascular areas, which results in intimal proliferation and degeneration of the vessel wall. Mononuclear cells infiltrate the area as the lesions progress to the subacute and chronic stages. Fibrinoid necrosis of the vessels ensues with compromise of the lumen, thrombosis, infarction of the tissues supplied by the involved vessel, and, in some cases, hemorrhage. As the lesions heal, there is collagen deposition, which may lead to further occlusion of the vessel lumen. Aneurysmal dilatations up to 1 cm in size along the involved arteries are characteristic of classic PAN. Granulomas and substantial eosinophilia with eosinophilic tissue infiltrations are not characteristically found and suggest allergic angiitis and granulomatosis (see below). online canadian pharmacy