French protocol for diagnosis and management (guidelines) of IgG4-related disease.

IgG4-related disease (IgG4-RD) is a recently described entity comprising pseudo-tumoral and inflammatory conditions that were previously considered separately. It is characterised by specific histological abnormalities, including polyclonal lymphoplasmacytic infiltration, fibrosis and contingent of IgG4+ plasma cells, often associated with elevated serum IgG4 levels and a good response to glucocorticoids. The clinical presentation is highly heterogeneous and requires a multidisciplinary assessment. The diagnosis is based on the identification of suggestive clinical or radiological signs, such as pancreatic, salivary or lacrimal gland involvement, retroperitoneal fibrosis, cholangitis, aortitis, lymphadenopathy or interstitial nephritis. It is also based on the search for laboratory evidence of abnormalities such as polyclonal gammopathy, elevated serum IgG4 levels and complement consumption, and is most often confirmed by organ biopsy. The disease progresses slowly, with gradual symptoms and a risk of sequelae related to fibrosis, particularly pancreatic or renal failure. Management is based on providing the patient with comprehensive information about symptoms, warning signs, adverse events of treatments, vaccination, diet and physical activity. Initial treatment consists of oral glucocorticoids at a dose of 0.4 to 0.6mg/kg/day for two to four weeks, followed by a gradual tapering until discontinuation at three months if possible. This treatment induces remission in more than 90% of cases, but relapses are common, sometimes requiring treatment with immunosuppressants. Follow-up includes regular consultations, imaging tests and laboratory workups, in particular serum IgG4 measurement, in order to monitor disease activity, predict relapses and prevent complications.