¹⁸F-FDG PET/CT discriminates whether rheumatoid arthritis patients are in ultrasound remission or not

¹⁸F-FDG PET/CT is used for cancer evaluation but can also quantify joint inflammation in RA. We evaluated its ability to identify patients in remission as defined by US.

Sixty RA patients underwent clinical, PET/CT and US evaluations (hands and wrists). For PET/CT, the maximum standardized uptake value (SUV_max) was determined. At the patient level, the highest SUV_max, number of PET-positive joints and cumulative SUV_max were recorded. US evaluation included gray-scale and power Doppler.

At the joint level, SUV_max was significantly lower when the joint was in US remission (P < 0.0001). Receiver operating characteristics curves identified a threshold of 0.86 to define joint remission with a high positive predictive value of 95.2%. At the patient level, the highest SUV_max and cumulative SUV were significantly lower in patients in US remission (respectively P = 0.0023 and P = 0.045). The highest SUV_max threshold of 2.36 demonstrated a high negative predictive value of 92.9% for determining US remission. For the cumulative SUV_max threshold, the negative and positive predictive values for determining US remission were both 73%. In contrast, these PET/CT parameters did not discriminate if a patient is in clinical remission or not.

PET/CT can identify RA patients in remission as defined by US. We show that the highest SUV_max and cumulative SUV are the two discriminative PET/CT parameters able to determine whether a patient is in US remission. This provides an additional advantage of PET/CT as an objective tool to evaluate RA.