Risk factors for extensive skeletal muscle uptake in oncologic FDG-PET/CT for patients undergoing a 4-h fast

Postprandial insulin secretion causes extensive skeletal muscle accumulation (ESMA) of fluorine-18 fluorodeoxyglucose (FDG), which adversely affects visual interpretation of FDG-PET/CT. We investigated factors related to ESMA despite a fast of at least 4 h.

A total of 3595 patients underwent FDG-PET/CT following a fast for at least 4 h. Among them, patients exhibiting ESMA affected by postprandial insulin and sex-matched and age-matched individuals without ESMA as controls were analysed. The following factors were compared: BMI, plasma glucose, presence of diabetes including suspected diabetes (DM-IS), presence of diabetes excluding suspected diabetes, insulin therapy, approximate volume of gastric food residue estimated by CT and residue including water. Multivariate analysis was performed among cases and controls made to fast identically for 4-5 h to assess independent risk factors.

Overall, 44 patients with ESMA and 100 controls were identified. The BMI of cases (22.0±3.0) was not significantly different from that of controls (21.5±2.9). Plasma glucose was significantly higher in cases (134.9±44.0 vs. 113.6±31.4 mg/dl; P=0.0050). Cases had a significantly higher proportion of DM-IS, presence of diabetes excluding suspected diabetes, insulin therapy, gastric food residue and residue including water (P<0.0001, P=0.0074, 0.0011, 0.0008 and 0.039, respectively). Logistic regression analysis among 29 cases and 100 controls who had undergone 4-5 h fasting revealed that DM-IS and gastric food residue were independent risk factors for ESMA with odds ratios of 5.14 (P=0.0006) and 5.39 (P=0.0014), respectively.

It would be preferable to fast for a longer time, especially for patients with glucose intolerance, and avoid heavy meals to reduce gastric residue.