Introduction: 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.
Exegesis: 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.
Conclusion: 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.