Person:

Hennessey, James

Background: In addition to its role in adaptive thermogenesis, brown adipose tissue (BAT) may protect from weight gain, insulin resistance/diabetes and metabolic syndrome. Prior studies have shown contradictory results regarding the influence of thyroid hormone (TH) levels on BAT volume and activity. The aim of this pilot study was to gain further insights regarding the effect of TH treatment on BAT function in adult humans by evaluating the BAT mass and activity prospectively in six patients, first in the hypothyroid and then in the thyrotoxic phase.

Methods: The study subjects underwent 18F-FDG PET-CT scanning after cold exposure to measure BAT mass and activity while undergoing treatment for differentiated thyroid cancer, first while hypothyroid following thyroid hormone withdrawal at the time of the radioactive iodine treatment and then 3-6 months after starting TH suppressive treatment when they were iatrogenically thyrotoxic. We measured thermogenic and metabolic parameters in both phases.

Results: All study subjects had detectable BAT under cold stimulation in both the hypothyroid and thyrotoxic state. The majority but not all (4 out of 6) subjects showed an increase in detectable BAT volume and activity under cold stimulation between the hypothyroid and thyrotoxic phase (total BAT volume: 72.0 ± 21.0 vs. 87.7 ± 16.5 mL, P = 0.25; total BAT activity 158.1 ± 72.8 vs. 189.0 ± 55.5 SUV*g/mL, P = 0.34). Importantly, circulating T3 was a stronger predictor of energy expenditure changes compared to cold-induced BAT activity.

Conclusions: Iatrogenic hypothyroidism lasting 2-4 weeks does not prevent cold-induced BAT activation, while the use of TH to induce thyrotoxicosis does not consistently increase cold-induced BAT activity. It remains to be determined which physiological factors besides TH play a role in regulating BAT function.

Introduction: The follicular variant of papillary thyroid cancer (FVPTC) can be noninvasive or invasive. The invasive form of FVPTC commonly harbors BRAF mutations whereas RAS mutations are more often associated with noninvasive FVPTC and a favorable clinical outcome. Case report A 47-year-old man presented with a metastasis to his right iliac bone as the initial manifestation of a 1.6 cm invasive FVPTC. After total thyroidectomy, the patient underwent additional treatment, including thyroid hormone suppressive treatment to non-detectable TSH levels, repeated courses of radioiodine treatment, external beam radiation, and treatment with the tyrosine kinase inhibitor sorafenib. Despite these therapeutic efforts, the disease progressed with growth of the iliac mass and additional metastatic spread to cervical and lumbar vertebrae causing increasing pain and disability. The patient succumbed to the disease four years after presentation. Retrospective next-generation sequencing of the primary tumor using a pan-cancer targeted mutation and gene fusion panel revealed NRAS Q61K mutation and no other oncogenic alterations. Discussion The study challenges the concept that thyroid neoplasms with isolated RAS mutations are often associated with favorable clinical behavior and may be candidates for conservative management. Conclusion: An isolated RAS mutation in invasive FVPTC may be associated with an aggressive clinical behavior.