Increased Atrial 18F-FDG Uptake on PET/CT Secondary to Atrial Flutter Precipitated by Ibrutinib

We report a case of marked biatrial ¹⁸ F-FDG uptake on PET/CT coinciding with the onset of symptomatic atrial flutter in a 77-year-old man with relapsed diffuse large B-cell lymphoma receiving ibrutinib. Serial imaging demonstrated normal atrial uptake before arrhythmia, marked uptake during atrial flutter, and complete normalisation following successful radiofrequency ablation. Atrial tachyarrhythmia represents an important and reversible cause of increased atrial FDG uptake and should prompt clinical and electrocardiographic correlation to avoid misinterpretation as cardiac disease involvement.