Diagnosis
How IgG4-RD is identified — the tests, criteria, and challenges involved.
Diagnosis requires clinical-pathological correlation
Definitive diagnosis of IgG4-RD requires rigorous clinical-pathological correlation because clinical assessments, laboratory evaluations, and imaging studies are often insufficient to distinguish neoplastic, inflammatory, and infectious mimickers.
IgG4-RD can cause swelling, lumps, or scarring in different organs, which is why it can resemble infections, cancers, or other autoimmune diseases. This overlap often makes diagnosis challenging.
Blood tests
Serum IgG4 elevation occurs in 55–97% of cases and correlates with the number of organs involved and the risk of relapse.
However, elevated serum IgG4 has poor specificity for diagnostic purposes, as it can be observed across a broad spectrum of neoplastic, infectious, and autoimmune diseases.
Imaging
Radiological findings are usually non-specific in most affected organs.
An exception is IgG4-related pancreatitis, where imaging classically shows a diffusely enlarged ‘sausage-shaped’ pancreas with a surrounding halo of oedematous tissue.
Histology — the gold standard
Because serological and radiological findings alone are insufficient, histological examination remains the mainstay for definitive diagnosis and should be performed whenever possible.
Characteristic findings include dense lymphoplasmacytic infiltration together with tissue fibrosis and obliterative phlebitis. Immunostaining is an essential part of histological diagnosis.
Conditions IgG4-RD is often mistaken for
Because IgG4-RD produces pseudotumor-like lesions across multiple organs, it is frequently misdiagnosed. Patients often receive incorrect cancer diagnoses, unnecessary surgeries, and years of confusion before a correct diagnosis is made.
The disease may initially present as a lymphoma, pancreatic cancer, cholangiocarcinoma, Sjögren’s syndrome, granulomatosis with polyangiitis, or inflammatory bowel disease, among others. This is why specialist expertise and tissue biopsy are so important.
Combining evidence
Diagnosis is most reliable when multiple elements are combined: clinical history, organ pattern, serum IgG4 levels, imaging findings, and — where possible — histopathological examination with immunostaining.
Specialist centres of excellence with experience in IgG4-RD are best placed to make or confirm a diagnosis. If you have not yet been seen by a specialist, speak to your doctor about a referral.
Carsten Sørensen
Patient & Treasurer, Denmark
As a co-founder and chair of the federation, I am proud to lead a community advocating for better recognition and care for IgG4-RD.
About the European Federation IgG4-RD
We are the bridge between you, the patient, be it as a direct member or through your own national association and the medical world and wider community. We connect knowledge, compassion, and advocacy across Europe for those affected by IgG4-Related Disease.
