Factors Affecting Brain Metabolism Measured with <sup>18</sup>FDG

An observational finding found a large variation in the brain SUV in patients with multiple myeloma undergoing PET/CT. The first hypothesis considered a toxic effect of chemotherapeutic agents, but no correlation was found with hematological signs of toxicity. Low brain FDG uptake has been described with anesthesia, but this was not relevant in this case. An alternative is the presence of a large FDG avid mass, but that was excluded. Since there was a question of chemotherapy toxicity, the metrics used for comparison were Hemoglobin levels (Hgb, g/dl), Erythrocyte count (RBC, M/μL), Lymphocytes absolute counts (Lymph#, K/μL) and % (lymph, %), Granulocytes Neutrophils, K/μL), age and C-reactive protein levels (CRP, g/L). The liver SUV (standardized uptake value) was included to eliminate unexpected global effects on the SUV values, since FDG uptake is a competitive system with a single source (plasma FDG levels). There was in fact no correlation between brain SUV and hepatic SUV, eliminating the so-called super scan effect. Further analysis, however, revealed a strong positive correlation with hemoglobin or RBC levels, but an inverse effect with Neutrophils, C-reactive proteins and age (in years). The results suggest that brain metabolism strongly depends on oxygen supply and may be depressed by general inflammatory diseases and independently with age. If the variation of glucose metabolism correlates with cognitive deficits (CD), considering general measures of good health may be a first step for relief of age related CD.