The prevalence of abnormal joint uptake in the lower extremities on 18F-FDG PET/CT in relation to patient’s age and BMI.

Objectives We determined the prevalence of abnormal 18F-FDG activity in the knee and hip joints and assessed their relation to patients’ age and body mass index (BMI).

Methods We randomly selected 176 patients (Pts) referred for whole-body PET/CT for evaluation of known/suspected malignancy (2007-present), after excluding Pts with bone metastasis. Pts were tabulated according to their age at the time of scanning into 4 groups (G). G1: 24 Pts, average (avg) age 15(5-19), 6 females (F)/18 males (M), average BMI (avg BMI) 25(15-39). G2: 51 Pts, avg age 30(20-39), 21F/30M, avg BMI 31(21-50). G3: 51 Pts, avg age 44(40-48), 21F/30M, avg BMI 28(18-43). G4: 50 Pts, avg age 60(59-63), 16F/34M, avg BMI 28(16-39). The maximum intensity projection (MIP) images were visually assessed for abnormal knee joint (medial/lateral compartments), patellar and trochanteric uptake. Total number of regions evaluated were 1056. Liver uptake was used as a reference. Findings were graded on a 4-point-scale: 1 (normal), 2 (mild/less than liver), 3 (moderate/equal to liver), and 4 (severe/higher than liver).

Results G4 and G2 have relatively similar abnormal activity (57%,54% respectively) despite difference in avg age, due to increased avg BMI (28,31 respectively). The male/female ratio in each group is not statistically significant.

Conclusions Preliminary results suggest that higher BMI even in a younger population is associated with increased knee/hip joint FDG uptake

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