The utility of FDG PET/CT in IgG4-related disease with a focus on coronary artery involvement

Our case series aims to study the growing use of FDG PET/CT in diagnostic evaluation and follow up of IgG4-RD with emphasis on patients presenting with coronary artery involvement. We conducted a search on the nuclear medicine and rheumatology service databases and identified patients with histologically proven IgG4-RD with FDG PET/CT performed at the Singapore General Hospital. The radiological, clinical, and laboratory findings of these patients were analyzed retrospectively. The series included ten male and two female patients. The commonest organ involved (five patients) was the pancreas. In three patients, coronary artery involvement manifested as soft tissue masses surrounding the arterial lumens. In these patients, histological diagnosis was established from alternative biopsy sites with abnormal metabolic activity on FDG PET/CT. Correlation between laboratory and metabolic imaging findings was not statistically significant in our series. Four patients had follow-up FDG PET/CT; three showed interval reduction in metabolic activity to baseline. One showed persistent abnormal metabolic activity before a rise in IgG4 levels. The metabolic imaging response was used to guide steroid dose. FDG PET/CT is a useful tool in evaluation and follow-up of IgG4-RD, particularly in identifying alternative biopsy sites in patients who present with coronary artery involvement. Hypermetabolic coronary artery masses on FDG PET/CT should raise clinical suspicion of IgG4-RD. As the coronary artery masses may not show decrease in size after treatment, FDG PET/CT is also useful for metabolic response assessment