Role of enteral nutrition in nonthyroidal illness syndrome: a retrospective observational study

Nonthyroidal Illness Syndrome in Patients With Short-Bowel Syndrome

BACKGROUND

Nonthyroidal illness syndrome (NTIS) is prevalent in critical illness and is associated with poor outcomes. However, only few studies have focused on the relationship between NTIS and short-bowel syndrome (SBS). The aim of this study was to investigate the prevalence, etiology, and prognosis of NTIS and its correlation with clinical variables in adult patients with SBS.

METHODS

Sixty-one eligible adults diagnosed with SBS, from December 2016 to December 2018, were retrospectively identified from a prospectively maintained database. Demographic and clinical characteristics (including thyroid hormones and nutrition variables) were evaluated for each participant.

RESULTS

The prevalence of NTIS in adults with SBS was 52.5%. Patients with NTIS tended to have a longer duration of hospital stay and poor survival, but the results were not significant. A decreased, standard thyroid-stimulating hormone index and sum activity of deiodinases and an increased secretory capacity by the thyroid were observed in the NTIS group. Receiver operating characteristic curve analysis showed that insulin-like growth factor-1 (IGF-1) had better performance for distinguishing NTIS from patients with euthyroidism, with an area under the curve of 0.862 (cutoff, 101.0; sensitivity, 0.813; and specificity, 0.800).

CONCLUSIONS

NTIS is a common complication in adult patients with SBS. Patients with NTIS tend to have a worse nutrition status and poor prognosis. A potential pituitary thyrotroph dysfunction and hypodeiodination condition may play a role in the pathophysiology of NTIS in SBS. Furthermore, IGF-1 is a meaningful predictor for distinguishing NTIS from euthyroid.

Higher Caloric Exposure in Critically Ill Patients Transiently Accelerates Thyroid Hormone Activation

INTRODUCTION

The inflammatory response of critical illness is accompanied by nonthyroidal illness syndrome (NTIS). Feeding has been shown to attenuate this process, but this has not been explored prospectively over time in critically ill patients.

OBJECTIVE

To explore the impact of calorie exposure on NTIS over time in critically ill patients.

METHODS

Mechanically ventilated patients with systemic inflammatory response syndrome (SIRS) were randomized to receive either 100% or 40% of their estimated caloric needs (ECN). Thyroid hormones were measured daily for 7 days or until intensive care unit discharge or death. Mixed level regression modeling was used to explore the effect of randomization group on plasma triiodothyronine (T3), reverse triiodothyronine (rT3), thyroxine (T4), and thyroid stimulating hormone (TSH), as well as the T3/rT3 ratio.

RESULTS

Thirty-five participants (n=19 in 100% ECN; n=16 in 40% ECN) were recruited. Adjusting for group differences in baseline T3/rT3 ratio, the parameters defining the fitted curves (intercept, linear effect of study day, and quadratic effect of study day) differed by randomization group (P = 0.001, P = 0.01, and P = 0.02 respectively). Plots of the fitted curves revealed that participants in the 100% ECN group had a 54% higher T3/rT3 ratio on postintervention day 1 compared with the 40% ECN group, a difference which attenuated over time. This was driven by a 23% higher plasma T3 and 10% lower plasma rT3 levels on postintervention 1.

CONCLUSIONS

Higher caloric exposure in NTIS patients transiently attenuates the drop of the plasma T3/rT3 ratio, an effect that is minimized and finally lost over the following 3 days of continued higher caloric exposure.

Thyroid Allostasis-Adaptive Responses of Thyrotropic Feedback Control to Conditions of Strain, Stress, and Developmental Programming

The hypothalamus-pituitary-thyroid feedback control is a dynamic, adaptive system. In situations of illness and deprivation of energy representing type 1 allostasis, the stress response operates to alter both its set point and peripheral transfer parameters. In contrast, type 2 allostatic load, typically effective in psychosocial stress, pregnancy, metabolic syndrome, and adaptation to cold, produces a nearly opposite phenotype of predictive plasticity. The non-thyroidal illness syndrome (NTIS) or thyroid allostasis in critical illness, tumors, uremia, and starvation (TACITUS), commonly observed in hospitalized patients, displays a historically well-studied pattern of allostatic thyroid response. This is characterized by decreased total and free thyroid hormone concentrations and varying levels of thyroid-stimulating hormone (TSH) ranging from decreased (in severe cases) to normal or even elevated (mainly in the recovery phase) TSH concentrations. An acute versus chronic stage (wasting syndrome) of TACITUS can be discerned. The two types differ in molecular mechanisms and prognosis. The acute adaptation of thyroid hormone metabolism to critical illness may prove beneficial to the organism, whereas the far more complex molecular alterations associated with chronic illness frequently lead to allostatic overload. The latter is associated with poor outcome, independently of the underlying disease. Adaptive responses of thyroid homeostasis extend to alterations in thyroid hormone concentrations during fetal life, periods of weight gain or loss, thermoregulation, physical exercise, and psychiatric diseases. The various forms of thyroid allostasis pose serious problems in differential diagnosis of thyroid disease. This review article provides an overview of physiological mechanisms as well as major diagnostic and therapeutic implications of thyroid allostasis under a variety of developmental and straining conditions.