The effect of hypothyroidism on referential background metabolic activity on 18F-FDG PET/CT

Abstract

Background: Background uptake activity is used as a reference to assess treatment response by positron emission tomography-computed tomography (PET/CT) with 2-deoxy-2- [F-18]fluoro-D-glucose ( 18 F-FDG).Prior studies have reported decreased liver and increased muscle 18 F-FDG uptake in patients with hyperthyroidism. We hypothesized that hyperthyroidism and hypothyroidism might have inverse effects on 18 F-FDG uptake on PET/CT. Methods: We recruited 36 patients with hypothyroidism and 36 age and gender-matched euthyroid participants. We recorded patient factors and background mean standardized uptake values normalized by lean body mass from the aortic blood pool, liver, and muscle. We compared the patient factors and background standardized uptake values normalized by lean body mass between hypothyroidism patients and the controls. We performed a multivariate analysis to determine the best predictors of the 3 different background standardized uptake values normalized by lean body mass. Results: Patients with hypothyroidism had higher liver standardized uptake values normalized by lean body mass (1.77±0.33 vs. 1.58±0.26, P=0.009) and aortic blood-pool standardized uptake values normalized by lean body mass (1.21±0.22 vs. 1.11±0.20, P=0.040) than the controls. In contrast, the muscle standardized uptake value normalized by lean body mass (0.50±0.09 vs. 0.54±0.09, P=0.044) of the patients with hypothyroidism was lower than that of the controls. The serum level of thyroid-stimulating hormone was an independent predictor of liver standardized uptake values normalized by lean body mass (β=0.356, P<0.001) and bloodpool standardized uptake values normalized by lean body mass (β=0.288, P=0.001). The serum level of free triiodothyronine was an independent predictor of muscle standardized uptake values normalized by lean body mass (β=0.310, P=0.002).Conclusions: PET/CT scans showed that hypothyroidism patients had increased liver and blood-pool 18 F-FDG uptake and decreased skeletal muscle 18 F-FDG uptake compared with euthyroid individuals. These alterations should be noted when a metabolic response to cancer treatment on PET/CT is determined.

Analyzing the value of delayed 18F-FDG PET/CT images in diagnosing small colorectal cancer liver metastases in patients with hypothyroidism based on diagnostic accuracy and image standardized uptake value

“…The criteria for hypothyroidism in this study were specified as increased TSH and decreased FT4 levels, which are also the diagnostic criteria of clinical hypothyroidism. Although examining patients with more severe hypothyroidism may be more favorable to corroborate our findings, as confirmed in the study by Yang et al [15], to avoid statistical bias, we excluded patients with severe medically induced hypothyroidism due to thyroidectomy or iodine treatment. Our study continues to show that even with mild hypothyroidism, the slower the liver tissue SUV mean decreases while clinical symptoms are present, the greater the SUV mean in delayed imaging.…”

“…tissue, which in turn leads to an increase in SUV mean and a slower decrease in liver tissue SUV mean with time. Indeed, a previous study [15] suggested that TSH can have an effect on the SUV value of normal liver tissue, but that study was not performed under tumor load. In our study, we discuss the SUV mean of normal liver tissue in hypothyroid patients under CRLM load, showing that FDG uptake by normal liver tissue in hypothyroid patients is still affected even under conditions of tumor load.…”

“…They concluded that hepatic FDG uptake is reduced in patients with hyperthyroidism and that FDG uptake is proportional to the severity of the hyperthyroid state. Studies have shown increased hepatic 18 F-FDG uptake on PET/CT scans in patients with hypothyroidism compared to patients with normal thyroid function [15]. In conclusion, abnormal thyroid function shows atypical SUV values on 18 F-FDG PET/CT images and correlates with the severity of thyroid disease.…”

Increased Pituitary Fluorine-18-Fluorodeoxyglucose Uptake in Patients with Differentiated Thyroid Cancer in Hypothyroidism versus under Recombinant Human Thyroid-Stimulating Hormone Stimulation

“…Previous studies have demonstrated that thyroid function can impact the metabolic activity of various tissues, as evidenced in 18 F-FDG PET/CT scans [6]. Under physiological conditions, the pituitary gland shows little uptake of 18 F-FDG; incidental findings of pituitary hypermetabolism are unusual, with a reported frequency of 0.8% [7][8][9][10].…”