Effects of age on red marrow metabolism as determined by FDG-PET imaging

Abstract

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Objectives: FDG uptake on the PET imaging reflects the degree of the metabolic activity of the tissues examined. Our objective was to determine the variation of patterns of metabolic activity of the bone marrow (BM) in different regions of the body and to assess the effects of normal aging.

Methods: A retrospective analysis of the FDG-PET scans of 71 patients (28 male, 43 female, age range: 15-85 years), with no history of pathological disorders, chemo or, radiation therapy and/or treatment with bone marrow suppressing or stimulating agents. We reviewed the blood sugar levels, renal, liver function tests and the CBC profile for all patients. Two patients were excluded as they had a high renal function test. PET scans were performed predominantly to evaluate a lung nodule or a breast mass. The ratio of the BM activity to background soft tissue activity was calculated using the maximum standardized uptake values (SUVmax). The activity of the BM was measured from the cervical, thoracic, lumbar and pelvic bones to calculate the average BM activity of each region and the total observed BM activity (TOBMA). One way ANOVA test was used to analyze the BM metabolic activity with age decades. p<0.01 was considered to be significant.

Results: The FDG BM uptake was uniform in all cases. The mean blood glucose level was 91 ±25 mg/dl. Both SUVmax in the BM and its ratio to the subcutaneous tissue showed the same trend with age. There was a slight increase in the TOBMA activity until the 3rd decade (8%), followed with a decrease during the 4th and 5th decade (-15.2%) and a more sharp decrease (-40.5%) after the age of 60 (p<0.01). The decreased activity after the age of 60 was profound in the BM of the cervical vertebrae (-48.4%) and the pelvic bones (-51.1%), in contrast to the BM in the lumbar vertebrae, which showed the least change (-33.2%). Low normal range in the CBC profile was noticed in 50% of patients above 60 years. The difference in the TOBMA was correlated with age (r= +0.55). We noticed that the metabolic activity in the lumber vertebrae contributes up to 33.3% of the TOBMA in the axial bones in all age decades.

Conclusions: In patients with no BM pathology, there is a decline in the metabolic activity of the BM which directly correlates with age. The most metabolically active and the least affected region with age is the BM in the lumbar vertebrae. These findings are should be considered when assessing focal and diffuse status which affects BM. All these data can help in the planning and the follow up of BM transplantation, and to study the effects of drugs.