Myeloperoxidase anti-neutrophil cytoplasmic antibody (MPO-ANCA)-positive microscopic polyarteritis (MPA) associated with Hashimoto's thyroiditis and increased serum rheumatoid factor

Abstract

An autopsy case of microscopic polyarteritis (MPA) associated with Hashimoto's thyroiditis that showed glomerular immunoglobulin and complement depositions and high titers of rheumatoid factor and myeloperoxidase anti-neutrophil cytoplasmic antibody (MPO-ANCA) is reported. A 72-year-old woman was admitted to our hospital because of renal failure that had deteriorated from a serum creatinine value of 175.8 to 1874.1 μmol/l in 4 weeks. Laboratory studies on admission revealed proteinuria, numerous red blood cells, granular casts and red blood casts in the urine, increased serum blood urea nitrogen (47.8 mmol/l), anemia (hemoglobin, 60 g/l), and thrombocytopenia (platelets, 71 × 10⁹/l). Emergency hemodialysis was started; however, the patient died on the fifth hospital day because of ventricular tachycardia, and an autopsy was performed. At autopsy, the patient was found to have had increased serum levels of immune complexes, rheumatoid factor, IgG rheumatoid factor, myeloperoxidase anti-neutrophil cytoplasmic antibody (MPO-ANCA), anti-thyroglobulin antibody, and anti-thyroid peroxidase antibody, and decreased serum complement levels. Microscopic examination revealed crescentic glomerulonephritis in almost all glomeruli, and positive granular deposits of IgG, IgA, IgM, C1q, C3, and C4 in the mesangium and along the capillary walls. Typical fibrinoid necrosis was found in the small arteries of the stomach, colon, small intestine, and bladder. Finally, Hashimoto's thyroiditis was noted. To our knowledge, this is the first case of MPO-ANCA-positive MPA associated with Hashimoto's thyroiditis and increased serum rheumatoid factor levels.