Low incidence of positive smooth muscle antibody and high incidence of isolated IgM elevation in Chinese patients with autoimmune hepatitis and primary biliary cirrhosis overlap syndrome: a retrospective study

Clinical data on patients diagnosed as autoimmune hepatitis and primary biliary cirrhosis overlap syndrome in our hospital from January 2001 to December 2006 were collected and analyzed.Overlap syndrome of autoimmune hepatitis and primary biliary cirrhosis accounted for 10.33% of patients with autoimmune liver diseases during the past six years. For these patients with overlap syndrome, xanthochromia, lethargy and anorexia were the predominant complaints; a low incidence (14/146) of smooth muscle antibody positivity and a high incidence (37/89) of isolated IgM elevation were the main serological characteristics.Overlap syndrome of autoimmune hepatitis and primary biliary cirrhosis was not rare in Chinese patients with clinical manifests of autoimmune liver diseases. Overlap of the diseases should not be disregarded when isolated IgM elevation was exhibited, and smooth muscle antibody might have little diagnostic significance in the overlap syndrome. If it was difficult to make a definite diagnosis, liver biopsy was necessary.Autoimmune hepatitis (AIH), primary biliary cirrhosis (PBC), and primary sclerosing cholangitis (PSC) are three major clinicopathologic entities of autoimmune liver diseases. Besides, some patients with autoimmune liver disease present with characteristics of a second autoimmune liver disease (i.e. AIH and PBC overlapping). These cases have been defined as overlap syndrome. Patients with overlap syndrome usually present with nonspecific symptoms, including lethargy, arthralgias, and myalgias. A combination of clinical and laboratory or pathologic criteria is necessary for the diagnosis of the disease. In the laboratory test, autoantibodies are the serological hallmarks. Serum antinuclear antibody (ANA), smooth muscle antibody (SMA) and antimitochondrial antibody (AMA) are routinely detected in these patients [1].Although combined features of both PBC and PSC have been reported in single cases, there is no clear evidence for the existence of an o