Physiologic 18F-fluorodeoxyglucose uptake in muscle: Unusual findings and the role of PET/CT

Learning Objectives 1. Recognize the spectrum of normal skeletal muscle ¹⁸F-FDG uptake. 2. Describe the mechanisms of ¹⁸F-FDG uptake in skeletal muscle. 3. Discuss the additional value of CT in differentiating physiologic from pathologic skeletal muscle uptake. 4. Improve the ability /level of confidence of nuclear physicians in interpreting PET-CT.

Summary: This educational exhibit presents illustrative cases of unusual physiologic skeletal muscle uptake with ¹⁸F-FDG PET/CT imaging. Skeletal muscle relies extensively on glycolysis for energy production and unusual patterns of physiologic ¹⁸F-FDG muscle activity may be an interpretative pitfall. It is thus important for nuclear physicians to be familiar with the spectrum of normal muscle uptake, including anatomic variants. Resting skeletal muscle demonstrates low level ¹⁸F-FDG uptake, whereas contraction or activation of muscle groups before, during, or after radiotracer injection can result in intense physiologic uptake. Focal physiologic muscle uptake may follow surgical/non-surgical trauma. Several mechanisms cause diffuse skeletal muscle uptake, including endogenous or exogenous insulin and muscle contraction in anxious patients. Careful patient preparation will reduce the number of cases with unwanted muscle uptake. Combined ¹⁸F-FDG PET/CT imaging allows for more precise anatomic and morphologic delineation of those muscular structures with increased ¹⁸F-FDG activity, compared to stand-alone PET. The additional value of CT in differentiating physiologic from pathological ¹⁸F-FDG uptake will be highlighted.