Heterogenous biochemical expression of hormone activity in subclinical/overt hyperthyroidism and exogenous thyrotoxicosis

Clinical characteristics and outcomes of an exogenous thyrotoxicosis epidemic in prison

Introduction

An outbreak of exogenous thyrotoxicosis is an uncommon cause of thyrotoxicosis. This study aimed to investigate the characteristics and outcomes of exogenous thyrotoxicosis and electrolyte imbalance in a prison during an outbreak of exogenous thyrotoxicosis in the Phitsanulok, Thailand prison.

Methods

This study collected cross-sectional data during an outbreak of thyrotoxicosis among inmates at Phitsanulok prison between 29 December 2019 and 17 January 2020. In the first phase, a total of 2815 prisoners were screened for thyroid-stimulating hormone (TSH), potassium levels and pulse rate. In the second phase, samples from 490 male prisoners were collected for test on thyroid function, serum electrolytes and urine electrolytes. Thyroglobulin levels were also measured in patients with thyrotoxicosis. A questionnaire was used to obtain patient information about signs and symptoms of thyrotoxicosis.

Results

The prevalence of subclinical thyrotoxicosis was 78.1%. The pulse rate was significantly higher in the subclinical thyrotoxicosis group. Weight loss, palpitation, muscle weakness and fatigue were found predominantly in the subclinical thyrotoxicosis group. The prevalence of hypokalaemia was 38.4%; however, there was no difference between subclinical thyrotoxicosis and normal TSH. The mean magnesium levels were significantly lower in the subclinical thyrotoxicosis group. Patients with hypokalaemia mainly showed potassium loss through the kidneys. Almost all patients with suppressed TSH levels had low to normal thyroglobulin levels. In addition, the mean of calculated total step-up deiodinase activity in patients with subclinical thyrotoxicosis was lower than 30 nmol/s, which was an additional clue to confirm exogenous thyrotoxicosis. The frozen meat during the outbreak had higher levels of thyroid hormone compared with the control group.

Conclusions

With an outbreak of thyrotoxicosis, most likely due to exposure to exogenous thyroid hormone in frozen meat, our findings have raised awareness of nutritional problems in prison. The development of surveillance systems to prevent outbreaks is urgently needed.

Minor perturbations of thyroid homeostasis and major cardiovascular endpoints—Physiological mechanisms and clinical evidence

It is well established that thyroid dysfunction is linked to an increased risk of cardiovascular morbidity and mortality. The pleiotropic action of thyroid hormones strongly impacts the cardiovascular system and affects both the generation of the normal heart rhythm and arrhythmia. A meta-analysis of published evidence suggests a positive association of FT4 concentration with major adverse cardiovascular end points (MACE), but this association only partially extends to TSH. The risk for cardiovascular death is increased in both subclinical hypothyroidism and subclinical thyrotoxicosis. Several published studies found associations of TSH and FT4 concentrations, respectively, with major cardiovascular endpoints. Both reduced and elevated TSH concentrations predict the cardiovascular risk, and this association extends to TSH gradients within the reference range. Likewise, increased FT4 concentrations, but high-normal FT4 within its reference range as well, herald a poor outcome. These observations translate to a monotonic and sensitive effect of FT4 and a U-shaped relationship between TSH and cardiovascular risk. Up to now, the pathophysiological mechanism of this complex pattern of association is poorly understood. Integrating the available evidence suggests a dual etiology of elevated FT4 concentration, comprising both ensuing primary hypothyroidism and a raised set point of thyroid function, e. g. in the context of psychiatric disease, chronic stress and type 2 allostatic load. Addressing the association between thyroid homeostasis and cardiovascular diseases from a systems perspective could pave the way to new directions of research and a more personalized approach to the treatment of patients with cardiovascular risk.