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New Treatments for Polyarteritis Nodosa

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) describes the syndrome.

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.

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.

Multiple organ systems are involved, and the clinicopathologic findings reflect the degree and location of vessel involvement and the resulting ischemic changes. As mentioned above, pulmonary arteries are not involved in classic PAN, and bronchial artery involvement is uncommon, whereas pulmonary capillaritis occurs frequently in microscopic polyangiitis. The pathology in the kidney in classic PAN is predominantly that of arteritis without glomerulonephritis. In contrast, glomerulonephritis is very common.

Clinical And Laboratory Manifestations

Nonspecific signs and symptoms are the hallmarks of classic PAN. Fever, weight loss, and malaise are present in over one-half of cases. Patients usually present with vague symptoms such as weakness, malaise, headache, abdominal pain, and myalgias. Specific complaints related to the vascular involvement within a particular organ system.

There are no diagnostic serologic tests for classic PAN. In over 75 percent of patients, the leukocyte count is elevated with a predominance of neutrophils. Eosinophilia is seen only rarely and, when present at high levels, suggests the diagnosis of allergic angiitis and granulomatosus. The anemia of chronic disease may be seen.

Diagnosis

The diagnosis of classic PAN is based on the demonstration of characteristic findings of vasculitis on biopsy material of involved organs. In the absence of easily accessible tissue for biopsy, the angiographic demonstration of involved vessels, particularly in the form of aneurysms of small and medium-sized arteries in the renal, hepatic, and visceral involvement.

Prognosis

The prognosis of untreated classic PAN as well as that of microscopic polyangiitis is extremely poor. The usual clinical course is characterized either by fulminant deterioration or by relentless progression associated with intermittent acute flare-ups. Death usually results from renal failure.

Treatment

Extremely favorable therapeutic results have been reported in classic PAN with the combination of prednisone, 1 mg/kg per day, and cyclophosphamide, 2 mg/kg per day. This regimen has been reported to result in up to a 90 percent long-term remission rate even following the discontinuation of therapy. In addition, long-term remissions have been reported in PAN associated with hepatitis B virus antigenemia using the antiviral agent.