Classical polyarteritis nodosa and microscopic polyarteritis with medium vessel involvement--a comparison of the clinical and laboratory features.

Microscopic polyarteritis may involve medium-sized and small blood vessels as well as arterioles, venules and capillaries. We have compared the clinical and laboratory features in patients with microscopic polyarteritis and medium vessel involvement, with the features found in patients with polyarteritis nodosa affecting medium vessels alone. In a 9-year period, 21 patients presented to our hospital with a form of polyarteritis. Seven had microscopic polyarteritis demonstrated histologically (6/7, 86%) and associated with dysmorphic urinary red cells (7/7, 100%), as well as medium vessel vasculitis demonstrated histologically (7/7) or by angiography (1/7, 14%). Five patients had polyarteritis nodosa with medium vessel vasculitis demonstrated histologically (3/5, 60%) or by angiography (2/5, 40%); and no evidence of a glomerular vasculitis on biopsy (2/7, 29%) or in the urinary sediment (0/7, 0%). The remaining 9 patients had microscopic polyarteritis but medium vessel involvement was not excluded by angiography. All patients with microscopic polyarteritis and medium vessel involvement had glomerular hematuria (> 100,000 glomerular RBC/ml), proteinuria > 0.5 g/24 hours), and an elevated serum creatinine (0.166 to 0.811 mmol/l). Other symptoms included fever (6/7, 86%), night sweats (5/7, 71%), gastrointestinal bleeding (4/7, 57%), proximal myopathy (3/7, 43%) and peripheral neuropathy (3/7, 43%). One patient (1/7, 14%) had hypertension. Anemia (6/7, 86%), a raised ESR (6/7, 86%), thrombocytosis (6/7, 86%), hypoalbuminemia (6/7, 86%) and abnormal liver function tests (6/7, 86%) were common. Two patients (29%) had an eosinophilia. All 5 individuals who were tested for ANCA were positive (2cANCA, 2pANCA and one pattern not described). In contrast, in patients with polyarteritis nodosa and medium vessel involvement alone, an elevated ESR was common (4/5, 80%) but fever (1/5, 20%), night sweats (0/5, 0%), proximal myopathy (1/5, 20%) and peripheral neuropathy (1/5, 20%) were seen infrequently; hypertension (1/5, 20%) and eosinophilia (1/5, 20%) were also uncommon; and ANCA were not demonstrated (0/3, 0%). Medium-sized vessel involvement is common in patients with microscopic polyarteristis, and these patients are more likely to have renal involvement and systemic symptoms, and be ANCA-positive, than patients with polyarteritis nodosa alone. Gastrointestinal symptoms are often seen in both groups.