Although joint manifestations are common in microscopic polyangiitis (MPA), including arthralgia reported in 15-65% of cases and arthritis in 6-17%, there have been only two published cases of polyarthritis as the first manifestation of the disease. We report on two new cases.
A 71-year-old woman had symmetric polyarthritis of the hands which initially suggested the existence of seronegative rheumatoid arthritis. A 52-year-old woman had seropositive asymmetric oligoarthritis. The diagnosis was not established until renal insufficiency appeared, prompting a renal biopsy which showed in both cases an extra-capillary glomerulonephritis and an anti-myeloperoxydase (p-ANCA) assay which was postive in both patients. The incidence and specificity of antineutrophil cytoplasmic antibodies (ANCA), including MPA, in rheumatoid arthritis are reviewed.
Our two observations show that in cases of polyarthritis or oligoarthritis with renal involvement, testing for and typing of ANCA should be performed so as not to misdiagnose vasculitis.