Two different types of antimitochondrial antibodies (anti-M2 and anti-M4) may not differentiate primary biliary cirrhosis (PBC) with prominent piecemeal necrosis from classical PBC.

Clinical and morphological features in 13 patients with primary biliary cirrhosis (PBC) who had two different types of antimitochondrial antibodies (PBC-specific, anti-M2 and mixed-form, anti-M4) in serum tested, were studied. Patients were allocated to two groups purely on the basis of the presence or absence of prominent piecemeal necrosis (PN) to elucidate the clinical significance of PN for differentiating mixed forms of chronic active hepatitis and PBC from classical PBC. Histological staging showed 10 stage I and 3 stage II. All cases had histological features of chronic non-suppurative destructive cholangitis. Prominent PN was encountered in 8 and bridging hepatic necrosis in 6. Granulomas were present in all cases without PN, but only in 3 of 8 cases with PN. Antimitochondrial antibody (AMA) was positive in all cases and anti-M2 was also positive in all but one. On the contrary, anti-M4 was positive in 2. Both anti-M2 and anti-M4 were simultaneously positive in 2, of which PN was present in only one. Therefore, anti-M4 did not relate to the presence or morphological severity of PN in PBC. Simultaneous increases in IgG and IgM were prominent features in PBC with PN.