E5195. Role of FDG-PET/CT in Measuring Global Arm Muscle Metabolism in Rheumatoid Arthritis and Control Subjects
  1. Saira Niazi; Hospital of University of Pennsylvania
  2. Shashi Singh; Stanford university
  3. Bimash Shrestha; KIST Medical College
  4. William Raynor; Rutgers Robert Wood Johnson Medical School
  5. Thomas Werner; Hospital of University of Pennsylvania
  6. Mona-Elisabeth Revheim; The Intervention Center, Rikshospitalet, Division for Technology
  7. Abass Alavi; Hospital of University of Pennsylvania
Rheumatoid arthritis (RA) is a chronic, systemic, autoimmune, inflammatory disorder that primarily involves synovial joints. FDG-PET/CT is ideally suited to quantify muscular glucose metabolism. In this study, we aimed to determine arm muscle metabolism in patients with RA compared to healthy subjects.

Materials and Methods:
Prospective FDG-PET/CT imaging data of 15 patients with RA (mean age 58 + 11.3 years, range 25–69 years, 12 men, 3 women) and 15 control subjects (mean age 55 + 10.2 years, range 25–66 years, 12 men, 3 women), matched for age and sex were compared. To obtain a desired consistent anatomic ROI for the right and left arm on the 3D maximum intensity projection view of the CT images, an upper and lower boundary was set at 4 cm below the humeral head (specifically, 4 cm below the proximal end of the greater tubercle) and 4 cm above the elbow joint (specifically, 4 cm above the distal end of the trochlea). A 3D automated ROI segmentation algorithm with Hounsfield unit (HU) threshold limits of 1–150 HU was used to segment the arm muscles on the combined PET/CT images after determining the upper and lower boundary on the arms. Wilcoxon signed-rank test was used to compare paired data such as laterality, whereas the Mann-Whitney U Test was used to compare differences between RA patients and healthy subjects.

A significantly higher uptake of FDG was found in the right compared to the left arm muscles of the healthy control subjects: right SUVmean 0.46 ± 0.14, left SUV mean 0.39 ± 0.15, p = 0.031. In contrast, there was no statistically significant difference between the uptake of FDG in the right and the left arm muscles of the RA patients: right SUVmean 0.57 ± 0.18, left SUVmean 0.62 ± 0.20, p = 0.0784. Overall, there was a significantly higher uptake of FDG in arm muscles of patients with. RA compared to healthy controls: RA SUVmean 0.59 ± 0.18 vs. SUVmean 0.43 ± 0.14 in healthy controls, p = 0.0065) indicating increase in muscle metabolism in the upper arm of patients with RA.

Our results indicate that patients with RA have significantly increased arm muscle metabolism compared to healthy control subjects. One possible explanation is involvement of multiple molecular pathways including cytokines, lymphocytes, macrophages, and fibroblasts, implicated in RA pathogenesis leading to inflammatory changes and corresponding increased uptake of FDG in RA-affected muscles. Future prospective studies should be aimed at examining FDG uptake in other muscle groups of the body as well as using FDG-PET/CT for monitoring effects of RA medication on muscular metabolism.