Spurious Uptake on 68Ga-Prostate-Specific Membrane Antigen PET/CT Due to Ankylosing Spondylitis; A Rare Pitfall in Imaging of Biochemical Recurrence of Prostate Cancer.

Bone is one of the most common sites of prostate cancer recurrence, and 68Ga-prostate-specific membrane antigen (PSMA) uptake by benign bone entities poses a diagnostic dilemma. We describe the case of a 60-year-old man with recurrence in a small presacral node on 68Ga-PSMA PET/CT. Of note, the images also demonstrated bilateral asymmetrical sacroiliac joint uptake. A history of ankylosing spondylitis was subsequently elicited, confirming the radiographic suspicion of sacroiliitis, therefore confirming the nonmalignant nature of 68Ga-PSMA uptake related to sacroiliitis rather than osseous recurrence from prostate carcinoma. 68Ga-PSMA uptake may indicate angioneogenesis in sacroiliitis and consequently may be helpful in assessing disease activity and therapy response.