IgG4-RD for Clinicians
About IgG4 Related Disease
IgG4-Related Disease (IgG4-RD) is a fibroinflamatory condition manifesting as inflammatory masses or organ dysfunction (Stone et al., 2012). Initially described in the pancreas, its systemic nature was recognised when identical histopathological features were identified in extrapancreatic organs (Kamisawa et al., 2003). Patients often have raised serum IgG4 levels, but this is not specific for IgG4-RD and there is no single diagnostic test. Even with a high index of clinical suspicion diagnosis can be challenging and be mistaken for malignancy. The disease is steroid responsive but often relapses after steroids are stopped. Untreated, the disease may lead to fibrosis and damage of affected organs. The Oxford IgG4-RD registry study is a national cohort study for patients with IgG4-RD which aims to better our understanding the natural history and pathogenesis of the condition.
The incidence and prevalence of IgG4-RD is not well characterised due to its variable presentation and the lack of a single diagnostic test. Most commonly it affects the pancreas, autoimmune pancreatitis type 1 (AIP). A Japanese population survey in 2011 estimated the annual incidence of AIP to be 1.4 per 100000 with a prevalence of 4.6 per 100000 (Kanno et al., 2015).
Up to 63% of patients have an allergic or atopic phenotype (Culver et al., 2017; Della Torre et al., 2014; Kamisawa et al., 2009) suggesting that an allergenic process is implicated in disease pathogenesis. 10% of patients have other autoimmune conditions (Huggett et al., 2014). A history of “blue collar” occupations has been associated with IgG4-RD suggesting exposure to toxins or chemicals may be important in disease development (de Buy Wenniger et al., 2014).
Signs and Symptoms
Clinical presentation is variable and dependent on the organ system or systems affected. Patients are most commonly male in the 6th decade (Ghazale et al., 2008). Pancreatobiliary disease can present with abdominal pain, obstructive jaundice or as an incidental mass on cross sectional imaging. Other symptoms and signs may include head and neck masses, dry mouth or breathlessness.