The immunobiology and clinical characteristics of IgG4 related diseases.

Having the characteristic features of elevated serum IgG4 levels and prominent infiltration of IgG4-positive plasma cells with fibrosis in lesions, Mikulicz's disease (MD) has been recognized as an IgG4-related disease (IgG4-RD). Although incidence of autoimmune pancreatitis (AIP), one of the organ characteristics of IgG4-RD, has been internationally reported, there are only a few such reports of IgG4-related MD. The limited number of reports might be attributable to the low recognition of IgG4-related MD as a clinical entity as well as its misdiagnosis as Sjögren's syndrome (SS). Thus, we compared several clinical features of MD with SS to improve proper clinical diagnosis of MD in the clinical setting. A total of 70 SS and 70 MD cases evaluated at Sapporo Medical University Hospital were retrospectively analyzed. In SS patients, sicca symptoms were the most frequent (87%), followed by articular symptoms (23%), while lacrimal and salivary gland swelling were a rare (10%) and transient manifestation. In contrast, lacrimal or salivary gland swelling was observed in all patients with MD. Although nearly 60% of MD patients complained of sicca syndrome, skin rash and arthralgia were rare symptoms. Hypergammaglobulinemia was recognized in both SS and MD patients, but the occurrence of autoantibodies in patients with IgG4-related MD was low. Extraglandular organ involvement, often involving the retroperitoneum, pancreas, kidney and lung, was often discovered at the time of IgG4-related MD diagnosis. Although corticosteroid therapy tended to delay the hypofunction of salivary gland in SS patients, recovery of decreased function of salivary glands were observed in IgG4-related MD patients. These results suggest the beneficial effect of aggressive corticosteroid intervention in patients with IgG4-related MD. Although SS and MD are both chronic inflammatory diseases affecting the lacrimal and salivary glands, their clinical features and corticosteroid responsiveness are different. Thus, differential diagnosis of these conditions is warranted.