Rare osteoarticular complications on [18F]FDG-PET/CT - following intravesical BCG immunotherapy for bladder cancer.

This case illustrates rare osteoarticular complications of Bacillus Calmette-Guérin (BCG) immunotherapy in a 55-year-old male with high-risk non-muscle-invasive bladder cancer (NMIBC). The patient was referred for 18F-fluorodeoxyglucose ([18F]FDG) positron emission tomography/computed tomography (PET/CT) to rule out bone metastases suspected on prior post-gadolinium magnetic resonance imaging (MRI). Although metastases were excluded, nearly symmetrical uptakes were detected in the costovertebral and costotransverse joints. Medical history revealed that the patient had been receiving intravesical instillations of BCG, the first-line therapy for high-risk NMIBC. The patient was diagnosed with reactive arthritis (ReA), a rare autoimmune complication of BCG, that was successfully treated with a nonsteroidal anti-inflammatory drug (NSAID).