(18)F-fluorodeoxyglucose Position Emission Tomography (FDG-PET) for Monitoring Disease Activity and Treatment Response in Idiopathic Retroperitoneal Fibrosis

Objective: To evaluate the value of (18)F-fluorodeoxyglucose positron emission tomography (FDG-PET) in monitoring disease activity and predicting treatment response in idiopathic retroperitoneal fibrosis (iRPF).

Patients And Methods: This prospective study was approved by the institutional review board. Informed consent was obtained from all patients. Twenty-six patients with iRPF receiving tamoxifen monotherapy underwent repeated FDG-PET (baseline and, if positive, at 3 months) and computed tomographic (CT) scanning (baseline, 4 and 8 months). Maximal RPF mass thickness in 3 different view directions was measured on each CT scan; FDG-uptake was semi-quantified using a visual 4-point scale. Initial and follow-up PET scan results were correlated with clinical, laboratory and CT scan follow-up data. Treatment outcome was the aggregate measure of clinical, laboratory and CT-documented response to tamoxifen.

Results: FDG-PET was positive in 20 patients. Patients with positive PET scan result had higher C-reactive protein level (P=0.02) and larger mass size (P=0.01) compared with patients with negative PET scan result. Visual PET score correlated with C-reactive protein level (P=0.002) and CT-documented mass thickness (P=0.04). Visual PET score decreased following treatment (P<0.01). This decrease correlated with decrease in ESR (P<0.001) but not with CT-documented mass regression. Positive predicting value (PPV) of initial positive PET scan result was 0.63; PPV of negative follow-up PET scan result in patients with initial positive PET scan result was 0.66.

Conclusion: FDG-PET is valuable in detecting (recurrent) disease activity. Short-term follow-up with FDG-PET cannot be routinely recommended for the therapeutic evaluation of RPF disease in tamoxifen-treated patients.