Clinical challenges in thyroid disease: Time for a new approach?

Higher Prevalence of "Low T3 Syndrome" in Patients With Chronic Fatigue Syndrome: A Case-Control Study

Chronic fatigue syndrome (CFS) is a heterogeneous disease with unknown cause(s). CFS symptoms resemble a hypothyroid state, possibly secondary to chronic (low-grade) (metabolic) inflammation. We studied 98 CFS patients (21-69 years, 21 males) and 99 age- and sex-matched controls (19-65 years, 23 males). We measured parameters of thyroid function, (metabolic) inflammation, gut wall integrity and nutrients influencing thyroid function and/or inflammation. Most remarkably, CFS patients exhibited similar thyrotropin, but lower free triiodothyronine (FT3) (difference of medians 0.1%), total thyroxine (TT4) (11.9%), total triiodothyronine (TT3) (12.5%), %TT3 (4.7%), sum activity of deiodinases (14.4%), secretory capacity of the thyroid gland (14.9%), 24-h urinary iodine (27.6%), and higher % reverse T3 (rT3) (13.3%). FT3 below the reference range, consistent with the "low T3 syndrome," was found in 16/98 CFS patients vs. 7/99 controls (OR 2.56; 95% confidence interval = 1.00-6.54). Most observations persisted in two sensitivity analyses with more stringent cutoff values for body mass index, high-sensitive C-reactive protein (hsCRP), and WBC. We found possible evidence of (chronic) low-grade metabolic inflammation (ferritin and HDL-C). FT3, TT3, TT4, and rT3 correlated positively with hsCRP in CFS patients and all subjects. TT3 and TT4 were positively related to hsCRP in controls. Low circulating T3 and the apparent shift from T3 to rT3 may reflect more severely depressed tissue T3 levels. The present findings might be in line with recent metabolomic studies pointing at a hypometabolic state. They resemble a mild form of "non-thyroidal illness syndrome" and "low T3 syndrome" experienced by a subgroup of hypothyroid patients receiving T4 monotherapy. Our study needs confirmation and extension by others. If confirmed, trials with, e.g., T3 and iodide supplements might be indicated.

Thyroid hormone regulation of intestinal epithelial stem cell biology

The gastrointestinal tract is a well-characterized target of thyroid hormones and thyroid hormone nuclear receptors TRs, as extensively described in the literature. The paradigm is its important remodelling in amphibians during thyroid hormone-dependent metamorphosis. Interestingly, several studies have described the conservation of this hormonal signal during intestinal development in mammals. Additional data suggested that it may also play a role in intestinal homeostasis, stem cell physiology and progenitor commitment as well as in tumour development. It is worth underlining that in the mammalian intestine the functionality of the TRα1 receptor is coordinated and integrated with other signalling pathways, such as Wnt and Notch, specifically at the level of stem/progenitor cell populations. Here, we summarize these data and concepts and discuss this new role for thyroid hormones and the TRα1 receptor in the biology of intestinal epithelial precursor cells.

Circulating thyroid hormones and associated metabolites in white whales (Delphinapterus leucas) determined using isotope-dilution mass spectrometry

Blood was sampled from nine free-ranging white whales (beluga whale, Delphinapterus leucas) from Svalbard, Norway during the summers of 2013 and 2014. Total concentrations of eleven thyroid hormones and metabolites were measured in serum using a novel liquid chromatography tandem mass spectrometry analytical method. Measurements of these compounds in plasma gave the same results as in serum. The three hormones found in highest concentrations were 3,3',5-triiodothyronine (T₃), 3,3',5'-triiodothyronine (rT₃) and thyroxine (T₄). Traces of associated metabolites were also found.