[IgG4-associated diseases : State of the art]

IgG4-related diseases are rare but the incidence is continuously increasing. The pathophysiology is only incompletely understood. Multiorgan involvement correlates with high relapse rates, high serum IgG4 levels and an aggressive disease course, which is why diagnostics and therapy must be carried out rapidly and efficiently according to international guidelines despite all the difficulties.

Currently the therapeutic standard is initial therapy (induction therapy) with glucocorticosteroids over a longer period of time and if necessary followed by low-dose maintenance therapy. Steroids are also the first choice therapy for management of relapses. Refractory disease courses are a rare but relevant problem.

The B‑cell depleting antibody rituximab has shown excellent results in terms of remission induction and also maintenance therapy. The good effectiveness profile is likely to change the current treatment regimen for IgG4-related diseases in the future.

The current diagnostic algorithms applicable for several organ systems are based on four major pillars: (i) patient history and physical examination, (ii) serological diagnostics, (iii) organ swelling in the appropriately selected imaging procedure and (iv) the histological picture as gold standard.

The currently used algorithms allow a diagnosis to be made in most cases.

IgG4-related diseases are a relevant differential diagnosis, particularly of malignant diseases. It is often a diagnosis by exclusion. An interdisciplinary approach is essential for rapid diagnostics and induction of therapy.

In Europe IgG4 serum levels are just one of several diagnostic criteria. Imaging studies should be chosen according to the organ and disease manifestations.