Background/Purpose: IgG4-related disease (IgG4-RD) is a systemic fibro-inflammatory condition characterized by unique pathological features that affect a wide variety of organs.  The disease process may be active long before patients present with symptoms from the mass effect of the IgG4-related lesions or the organ damage. Morphologic and functional imaging studies are increasingly used in the diagnosis and monitoring of response to therapy in inflammatory diseases. Positron-emission tomography/computed tomography (PET/CT) enables the acquisition of whole-body images and provides functional information about disease activity. The purpose of our study was to describe the PET/CT findings in patients with histologically-proven IgG4-RD and to evaluate their correlation with disease activity.

Materials/Methods: We searched the IgG4-RD Registry at Massachusetts General Hospital. Between March 2007 and May 2012, 20 patients (7 female and 13 male; median age 57 years, range 27-81), underwent whole body ¹⁸F-fluoro-2-deoxy-D-glucose positron-emission tomography/computed tomography (FDG PET-CT) imaging. All 20 patients had diagnoses of IgG4-RD based on the characteristic histology and immunostaining findings for this condition. We compared the sites of disease activity identified by PET/CT to the sites identified by their clinicians through symptoms, signs, laboratory findings, and other imaging studies. 

Results: Patients presented with various symptoms including: flank/back pain (7 patients), face swelling (3), neck swelling (3), proptosis (2), cough (2), weight loss (2), sinus congestion (2), and dry mouth/eyes (1).  Thirteen of 20 patients (65%) had multi-organ disease at presentation, affecting some combination of the pancreas, bile ducts, liver, gallbladder, lung, salivary glands, orbitals, aorta, thyroid, kidney, retroperitoneum, and lymph nodes.  The mean number of organs involved among patients with multi-organ disease was 4.1 (ranging 2-7 organs).  Seven patients (35%) had localized disease at presentation (5 RPF, 1 lymphadenitis, 1 orbital pseudotumor).

The serum IgG4 was elevated in 8 patients at the time of PET-CT imaging (mean 635.6 mg/dL). FDG PET was positive in all 20 patients (mild to intense uptake in 19 and low in 1 subject). In 17/20 patients (85%), FDG uptake was concordant with clinical manifestations of active inflammation. In addition 7/20 patients (35%) had FDG uptake in organs not suspected of involvement on a clinical basis alone (RPF, lymph nodes, thoracic aorta, lung, lacrimal glands and nasopharynx).

Conclusion: In IgG4-RD, FDG PET-CT is a sensitive imaging tool for the detection of subclinical disease.  This modality can demonstrate additional sites of disease not obvious by clinical presentation or on conventional CT imaging, therefore providing a more complete assessment of the extent of organ disease. It’s utility as a tool for monitoring treatment response and guiding therapy requires prospective studies.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/utility-of-pet-ct-imaging-in-igg4-related-disease/