Methodology Development for Investigating Pathophysiological [¹⁸F]-FDG Muscle Uptake in Patients with Rheumatic...

Area of Science:

• Nuclear Medicine
• Radiopharmaceuticals
• Rheumatology

Background:

• Rheumatic musculoskeletal diseases (RMDs) involve complex pathophysiological processes affecting muscle tissue.
• Assessing muscle metabolic activity, specifically glucose uptake, can provide insights into disease mechanisms.
• F18-fluordeoxyglucose (FDG) Positron Emission Tomography and Computed Tomography (PET/CT) is a functional imaging technique that visualizes glucose metabolism.

Purpose of the Study:

• To explore the qualitative and quantitative assessment of FDG PET/CT scans for evaluating muscle glucose uptake in patients with RMDs.
• To determine the feasibility of quantitatively assessing FDG uptake in muscles across rheumatoid arthritis (RA), osteoarthritis (OA), and idiopathic inflammatory myositis (IIM) compared to controls.
• To compare different methods for quantitative assessment of muscle FDG uptake.

Main Methods:

• Retrospective analysis of whole-body FDG PET/CT scans from patients with RA (n=11), OA (n=10), IIM (n=10), and non-RMD controls (n=11).
• Qualitative assessment to identify regions of high FDG uptake.
• Quantitative assessment using fixed volume-of-interest (VOI) and hotspot VOI methods to determine standardized uptake values (SUVs) in specific muscle groups.

Main Results:

• Heterogeneous FDG uptake patterns were observed in 93% of quadriceps and hamstring muscles.
• The hotspot VOI method demonstrated higher sensitivity in detecting differential muscle FDG uptake compared to the fixed VOI method.
• Patients with IIM showed the highest FDG uptake, followed by OA and RA patients, indicating increased muscle glucose metabolism in RMDs.

Conclusions:

• FDG PET/CT allows for qualitative and quantitative differentiation of muscle glucose uptake in patients with RA, OA, and IIM.
• The hotspot method and SUVpeak are recommended for accurate quantitative assessment of muscle FDG uptake.
• Elevated FDG uptake in multiple muscle groups suggests underlying pathophysiological glucose metabolism in RMD-affected muscles.