Microscopic polyangiitis associated with primary biliary cirrhosis: a causal or casual association?

The association between microscopic polyangiitis (MPA) and primary biliary cirrhosis (PBC) has seldom been reported. We describe a patient with PBC and MPA who presented with polyarthritis and pulmonary nodules followed by pauci-immune crescentic glomerulonephritis and liver dysfunction. Detection of p-ANCA, antimyeloperoxidase, and antimitochondrial antibodies along with liver and renal histopathology allowed a diagnosis of MPA and PBC. We also discuss 2 other cases that could be unrecognized associations of both diseases. Further reports are necessary to clarify if the coexistence between PBC and MPA is causal or casual.