An update on non-thyroidal illness syndrome

The non-thyroidal illness syndrome (NTIS) was first reported in the 1970s as a remarkable ensemble of changes in serum TH (TH) concentrations occurring in probably any severe illness. Ever since, NTIS has remained an intriguing phenomenon not only because of the robustness of the decrease in serum triiodothyronine (T3), but also by its clear correlation with morbidity and mortality. In recent years, it has become clear that (parenteral) feeding in patients with critical illness should be taken into account as a major determinant not only of NTIS but also of clinical outcome. Moreover, both experimental animal and clinical studies have shown that tissue TH concentrations during NTIS do not necessarily reflect serum low TH concentrations and may decrease, remain unaltered, or even increase according to the organ and type of illness studied. These differential changes now have a solid basis in molecular studies on organ-specific TH transporters, receptors and deiodinases. Finally, the role of inflammatory pathways in these non-systemic changes has begun to be clarified. A fascinating role for TH metabolism in innate immune cells, including neutrophils and monocytes/macrophages, was reported in recent years, but there is no evidence at this early stage that this may be a determinant of susceptibility to infections. Although endocrinologists have been tempted to correct NTIS by TH supplementation, there is at present insufficient evidence that this is beneficial. Thus, there is a clear need for adequately powered randomized clinical trials (RCT) with clinically relevant endpoints to fill this knowledge gap.

Determinants of deranged thyroid function parameters in children admitted for management of diabetic ketoacidosis/diabetic ketosis

BACKGROUND

Euthyroid sick syndrome (ESS) frequently arises in children admitted with diabetic ketoacidosis/diabetic ketosis (DKA/DK). This study evaluates the interplay of various metabolic factors with occurrence of deranged thyroid function tests in children suffering from DKA/DK.

METHODS

98 DKA and 96 DK pediatric patients were selected from hospital records. Those on thyroxine replacement, with overt hypothyroidism, or with positive anti-thyroperoxidase (TPO) antibody were excluded. Tests for liver function, renal function, lipid profile, serum osmolarity, thyroid function, c-peptide levels, and glycosylated hemoglobin were done on all patients. Children were divided into euthyroid (n = 88) and ESS groups (n = 106).

RESULTS

The ESS group had a higher level of white blood cell count (WBC), plasma glucose (PG), beta-hydroxybutyric acid (β-HB), triglyceride (TG), anion gap (AG), glycosylated hemoglobin (HbA1c) and a lower level of HCO₃^-, prealbumin (PA), and albumin (ALB) compared with the euthyroid group (P < 0.05). Free T3 (FT3) levels were significantly correlated to β-HB, HCO₃^-, AG, PA, and HbA1c (r = - 0.642, 0.681, - 0.377, 0.581, - 0.309, respectively; P < 0.01). Free T4 (FT4) levels were significantly correlated to β-HB, HCO₃^-, and ALB levels (r = - 0.489, 0.338, 0.529, respectively; P < 0.01). TSH levels were significantly affected by HCO₃^- only (r = - 0.28; P < 0.01). HCO₃^- level was the most important factor deciding euthyroid or ESS on logistic regression analysis (OR = 0.844, P = 0.004, 95%CI = 0.751-0.948).

CONCLUSIONS

Lower levels of free thyroid hormones and occurrence of ESS were associated with a higher degree of acidosis in children with DKA/DK.

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.

Nonthyroidal illness in critically ill children

PURPOSE OF REVIEW

This review summarizes recent literature on nonthyroidal illness syndrome (NTI) and outcome of pediatric critical illness, to provide insight in pathophysiology and therapeutic implications.

RECENT FINDINGS

NTI is typically characterized by lowered triiodothyronine levels without compensatory TSH rise. Although NTI severity is associated with poor outcome of pediatric critical illness, it remains unclear whether this association reflects an adaptive protective response or contributes to poor outcome. Recently, two metabolic interventions that improved outcome also altered NTI in critically ill children. These studies shed new light on the topic, as the results suggested that the peripheral NTI component, with inactivation of thyroid hormone, may represent a beneficial adaptation, whereas the central component, with suppressed TSH-driven thyroid hormone secretion, may be maladaptive. There is currently insufficient evidence for treatment of NTI in children. However, the recent findings raised the hypothesis that reactivation of the central NTI component could offer benefit, which should be tested in RCTs.

SUMMARY

NTI in critically ill children can be modified by metabolic interventions. The peripheral, but not the central, component of NTI may be a beneficial adaptive response. These findings open perspectives for the development of novel strategies to improve outcome of critical illness in children.

Non-Thyroidal Illness Syndrome in Critically Ill Children: Prognostic Value and Impact of Nutritional Management

INTRODUCTION

Non-thyroidal illness (NTI), which occurs with fasting and in response to illness, is characterized by thyroid hormone inactivation with low triiodothyronine (T3) and high reverse T3 (rT3), followed by suppressed thyrotropin (TSH). Withholding supplemental parenteral nutrition early in pediatric critical illness (late-PN), thus accepting low/no macronutrient intake up to day 8 in the pediatric intensive care unit (PICU), accelerated recovery compared to initiating supplemental parenteral nutrition early (early-PN). Whether NTI is harmful or beneficial in pediatric critical illness and how it is affected by a macronutrient deficit remains unclear. This study investigated the prognostic value of NTI, the impact of late-PN on NTI, and whether such impact explains or counteracts the outcome benefit of late-PN in critically ill children.

METHODS

This preplanned secondary analysis of the Early versus Late Parenteral Nutrition in the Pediatric Intensive Care Unit randomized controlled trial quantified serum TSH, total thyroxine (T4), T3, and rT3 concentrations in 982 patients upon PICU admission versus 64 matched healthy children and in 772 propensity score-matched early-PN and late-PN patients upon admission and at day 3 or last PICU day for shorter PICU stay. Associations between thyroid hormone concentrations upon admission and outcome, as well as impact of late-PN on NTI in relation with outcome, were assessed with univariable analyses and multivariable logistic regression, linear regression, or Cox proportional hazard analysis, adjusted for baseline risk factors.

RESULTS

Upon PICU admission, critically ill children revealed lower TSH, T4, T3, and T3/rT3 and higher rT3 than healthy children (p < 0.0001). A more pronounced NTI upon admission, with low T4, T3, and T3/rT3 and high rT3 was associated with higher mortality and morbidity. Late-PN further reduced T4, T3, and T3/rT3 and increased rT3 (p ≤ 0.001). Statistically, the further lowering of T4 by late-PN reduced the outcome benefit (p < 0.0001), whereas the further lowering of T3/rT3 explained part of the outcome benefit of late-PN (p ≤ 0.004). This effect was greater for infants than for older children.

CONCLUSION

In critically ill children, the peripheral inactivation of thyroid hormone, characterized by a decrease in T3/rT3, which is further accentuated by low/no macronutrient intake, appears beneficial. In contrast, the central component of NTI attributable to suppressed TSH, evidenced by the decrease in T4, seems to be a harmful response to critical illness. Whether treating the central component with TSH releasing hormone infusion in the PICU is beneficial requires further investigation.

[Euthyroid sick syndrome: an important clinical problem]

Despite absence of thyroid disease, patients with non-thyroidal illness frequently have changes in serum thyroid hormone measurements that may suggest thyroid dysfunction. These abnormalities include low serum triiodothyronine, high reverse triiodothyronine and usually normal or inappropriately low thyrotropin and thyroxine levels. The degree of thyroid function impairment correlates with disease severity and low levels of thyroid hormones, particularly thyroxine, predict a poor prognosis. Considerable controversy exists on whether the fall in thyroid hormone levels is adaptive and simply a normal, physiologic response to conserve energy, or whether it is maladaptive and requires treatment. Interpretation of thyroid function tests in the critically ill patient can be difficult and differential diagnosis of euthyroid sick syndrome is challenging, particularly in patients in whom no test results from before the onset of a critical illness are available. In recent years, some questions associated with euthyroid sick syndrome have been better understood. The purpose of this article is to review the present state of knowledge on the pathogenesis, diagnosis and clinical consequences of euthyroid sick syndrome to discuss pros and cons of its treatment.

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

BACKGROUND

The nonthyroidal illness syndrome (NTIS) is prevalent among patients with enterocutaneous fistula and is associated with poor outcomes. The present study aimed to explore the role of enteral nutrition (EN) therapy on thyroid function among patients with enterocutaneous fistula and NTIS.

METHODS

We conducted a retrospective observational study among patients with enterocutaneous fistula between January 2013 and April 2014. All enrolled patients received EN therapy. Thyroid function and other parameters were measured.

RESULTS

After administration of 4 weeks of EN therapy, NTIS was resolved in 66 patients (Group A), while it persisted in 14 patients (Group B). The overall treatment success rate was 82.50 %. There were no significant differences between groups A and B at baseline for all parameters, except for the time from admission to start of EN therapy. The logistic analysis revealed that the time from admission to start of EN therapy was a significant independent indicator for achieving resolution of NTIS in our cohort.

CONCLUSIONS

This retrospective observational cohort study demonstrated that EN therapy can aid in the resolution of NTIS among patients with enterocutaneous fistula. These findings confirm the benefit of EN in the treatment of enterocutaneous fistula.

Non-thyroidal illness in the ICU: a syndrome with different faces

BACKGROUND

Critically ill patients typically present with low or low-normal plasma thyroxine, low plasma triiodothyronine (T3), increased plasma reverse T3 (rT3) concentrations, in the absence of a rise in thyrotropin (TSH). This constellation is referred to as nonthyroidal illness syndrome (NTI). Although it is long known that the severity of NTI is associated with risk of poor outcomes of critical illness, the causality in this association has not been well investigated.

SUMMARY

In this narrative review, the different faces of NTI during critical illness are highlighted. Acute alterations are dominated by changes in thyroid hormone binding, peripheral thyroid hormone uptake, and alterations in the expression and activity of the type-1 and type-3 deiodinases. It was recently shown that at least part of these acute changes are brought about by concomitant macronutrient restriction, and this part appears adaptive and beneficial. However, the face of the NTI in the prolonged phase of critical illness is different, when patients are fully fed but continue to depend on intensive medical care. In that prolonged phase of illness, hypothalamic thyrotropin releasing hormone (TRH) expression is suppressed and explains reduced TSH secretion and whereby reduced thyroidal hormone release. During prolonged critical illness, and in the presence of adequate nutrition, several tissue responses could be interpreted as compensatory to low thyroid hormone availability, such as increased expression of monocarboxylate transporters, upregulation of type-2 deiodinase activity, and increased sensitivity at the receptor level. Infusing hypothalamic releasing factors in these prolonged critically ill patients can reactivate the thyroid axis and induce an anabolic response.

CONCLUSIONS

It is clear that the name "NTI" during critical illness refers to a syndrome with different faces. Tolerating the early "fasting response" to critical illness and its concomitant changes in thyroid hormone parameters appears to be wise and beneficial. This thus applies to the NTI present in the majority of the patients treated in intensive care units. However, the NTI that occurs in prolonged critically ill patients appears different with regard to both its causes and consequences. Future studies should specifically target this selected population of prolonged critically ill patients, and, after excluding iatrogic drug interferences, investigate the effect on outcome of treatment with hypothalamic releasing factors in adequately powered randomized controlled trials.

Common endocrine issues in the pediatric intensive care unit

Thyroid hormone is central to normal development and metabolism. Abnormalities in thyroid function in North America often arise from autoimmune diseases, but they rarely present as critical illness. Severe deficiency or excess of thyroid hormone both represent life-threatening disease, which must be treated expeditiously and thoroughly. Such deficiencies must be considered, because presentation may be nonspecific.

[Nonthyroidal illness syndrome in acute bacterial endotoxicosis: pathogenesis and methods of correction]

Nonthyroidal illness syndrome is characterized by alterations of thyroid status inpatients with severe nonthyroidal illness who are clinically euthyroid. Mechanisms of nonthyroidal illness syndrome are poorly understood and controversial. Our investigations on nonthyroidal illness syndrome in acute endotoxicosis revealed two principal mechanisms of its development. The peripheral mechanism is the first to develop and referred to disturbance of thyrocytes secretory cycle due to increase of thyroglobulin synthesis, endocytosis and decrease of its proteolytic cleavage. It manifests with drop of serum thyroxine, not triiodthyronine, and increase of serum thyroid stimulating hormone. The central mechanism is associated with hypothalamic-pituitary hypofunction developed simultaneously with systemic inflammatory response. Rate of supplementation of the peripheral mechanism with the central one accounts for different types of nonthyroidal illness syndrome with high, normal and low serum levels of thyroid stimulating hormone. Our research showed that thyroid hormone replacement in nonthyroidal illness syndrome could only suppress thyroid function. Unlike thyroid hormones administration of thyroid stimulating hormone restores thyroid hormone secretion in nonthyroidal illness syndrome, decreases endotoxinemia and secretion of proinflammatory cytokines and improves liver function.

Low triiodothyronine syndrome: a prognostic marker for outcome in sepsis?

There is ongoing controversy as to whether hormonal changes of the euthyroid sick syndrome are predictors of poor outcome in sepsis and critical illness. In this prospective study, the prognostic accuracy of thyroid hormone levels in 103 critically ill adult patients on admission and during follow up in a medical intensive care unit (ICU) was assessed and was compared to clinical risk scores, namely, the acute physiology and chronic health evaluation and the simplified acute physiology score. Median T3 levels on admission to the ICU were lower in the 53 septic cases [0.9 nmol/l (IQR 0.6-1.1)] as compared with the 50 patients with a systemic inflammatory response syndrome [1.2 nmol/l (IQR 0.8-1.4), P < 0.001]. The lowest T3 levels were found in patients with severe sepsis [0.8 nmol/l (IQR 0.55-0.95)] and septic shock [0.8 nmol/l (IQR 0.6-1.0)]. There was no difference in T3 and free thyroxin (fT4) levels on admission in non-survivors compared with survivors overall and in subgroups of patients with SIRS and sepsis. During the follow up, fT4 levels decreased significantly in non-survivors, while they increased in survivors [fT4 difference -1.3 (IQR -2.5 to 0.2) vs. 0.8 (IQR -0.85 to 4.1), P = 0.003]. In addition, on the day of death, non-survivors had lower T3 and fT4 levels as compared with survivors (P = 0.04 and P = 0.02). T3 and fT4 levels on admission were not prognostic in this cohort of critically ill patients. A decrease in fT4 levels in the course of disease, however, may point to adverse outcome.

Thyroid function during critical illness

The metabolic support of the critically ill patient is a relatively new target of active research and little is as yet known about the effects of critical illness on metabolism. The nonthyroidal illness syndrome, also known as the low T3 syndrome or euthyroid sick syndrome, describes a condition characterized by abnormal thyroid function tests encountered in patients with acute or chronic systemic illnesses. The laboratory parameters of this syndrome include low serum levels of triiodothyronine (T3) and high levels of reverse T3, with normal or low levels of thyroxine (T4) and normal or low levels of thyroid-stimulating hormone (TSH). This condition may affect 60 to 70% of critically ill patients. The changes in serum thyroid hormone levels in the critically ill patient seem to result from alterations in the peripheral metabolism of the thyroid hormones, in TSH regulation, in the binding of thyroid hormone to transport-protein and in receptor binding and intracellular uptake. Medications also have a very important role in these alterations. Hormonal changes can be seen within the first hours of critical illness and, interestingly, these changes correlate with final outcome. Data on the beneficial effect of thyroid hormone treatment on outcome in critically ill patients are so far controversial. Thyroid function generally returns to normal as the acute illness resolves.

The role of thyroid dysfunction in the critically ill: a review of the literature

During critical illness, patients with no known history of thyroid disorders may experience multiple alterations in their serum thyroid hormone levels. Such alterations have been termed sick euthyroid syndrome or, more recently, non-thyroidal illness syndrome (NTIS). The laboratory parameters of NTIS usually include low serum levels of triiodothyronine (T3), normal or low serum levels of thyroxine (T4) and normal or low serum levels of thyroid-stimulating hormone (TSH). The magnitude of the alteration in thyroid function correlates with the severity of the illness and its outcomes in critically ill patients with NTIS. The pathogenetic mechanisms involved in NTIS include a decreased conversion of T4 to T3 in extrathyroidal tissues and alterations in thyroid hormones' binding to serum proteins. In cases of protracted critical illness, a decrease in the pulsatile frequency of TSH secretion, resulting from reduced thyrotropin-re leasing hormone (TRH) release by the hypothalamus, may also occur. Several medications or clinical conditions that are commonly present in critically ill patients may be responsible for lowering serum concentrations of thyroid hormone. Among those who study the condition, the question of whether NTIS is a protective adaptation of the organism to illness or a maladaptive response to a stressful insult remains unanswered. In either case, thyroid hormone abnormalities are likely to play a role in the critically ill patient.However, there is currently no convincing evidence to suggest that restoring physiological thyroid hormone concentrations in unselected patients with NTIS would be beneficial.

Nonthyroidal illness syndrome in children

Neuroendocrine changes in the hypothalamic-pituitary-thyroid axis during critical illness result in nonthyroidal illness syndrome (NTIS) characterized by abnormal thyrotropin (TSH) and thyroid hormone levels. Studies looking at the natural history of neuroendocrine changes during critical illness have revealed the presence of NTIS. NTIS has been described in a variety of patient settings. Many studies have tried to uncover the pathophysiology behind NTIS and several theories are proposed. Whether NTIS requires treatment or intervention is still controversial and the results of the treatment studies are arguably mixed. Whether implicitly stated or not, the underlying purpose of all the natural history, pathophysiology, or treatment studies is to determine whether NTIS is adaptive or maladaptive. Some studies have illustrated a correlation between illness severity and the degree of NTIS but a cause and effect relationship is still elusive. The human studies can be divided between those with either adult or pediatric subjects, with much less data available in the latter. This review examines the available literature on NTIS with an emphasis on the pediatric literature.

Euthyroid pretibial myxedema and EMO syndrome

EMO syndrome is a rare extrathyroid syndrome, seen in only 1% of patients affected by extrathyroid complications of Graves' disease. A 73-year-old woman presented with a 1-year history of asymptomatic local swellings on her legs and feet. Physical examination revealed moderate proptosis and multiple, firm subcutaneous nodules of 1 to 5 cm in diameter located on the anterior and medial aspects of the shins and on feet. The patient had a history of bilateral knee arthroplasty 5 years ago. Histopathologic examination showed deposition of mucin and perivascular lymphocytic infiltration in the dermis. Dermatologic and pathologic findings were consistent with pretibial myxedema. Laboratory tests showed normal thyroid stimulating hormone (TSH) and serum free T3 and T4 levels. The TSH receptor antibody titer was elevated. Thus, with all these findings she was diagnosed with exophthalmia, myxedema, and hypertrophic osteoarthropathy (EMO) syndrome. The lesions were completely treated with three monthly intralesional corticosteroid injections and at the 4-month follow-up no recurrence was observed. Only three euthyroid cases with pretibial myxedema have been reported in the literature. Patients that have asymptomatic pretibial nodular or plaque lesions should be investigated with an ophthalmologic examination and laboratory workup to clarify a possible underlying thyroid gland disease and EMO syndrome.

Non thyroidal illness: to treat or not to treat?

In critically ill patients, pronounced alterations in the hypothalamic-pituitary-thyroid axis occur without any evidence for thyroid disease. T3 decreases and rT3 increases within a few hours of the onset of disease. Severity and duration of disease are related to the magnitude of these changes. This manuscript discusses whether these changes in thyroid hormone levels during critical illness should be treated, and was in part published elsewhere.

Frequency and outcome of patients with nonthyroidal illness syndrome in a medical intensive care unit

Acute and chronic critical conditions are associated with reduced serum levels of free triiodothyronine (FT(3)), free thyroxine FT(4), and thyrotropin, known as nonthyroidal illness syndrome (NTIS). It is still controversial whether these changes reflect a protective mechanism or a maladaptive process during prolonged illness. However, larger studies to determine the prevalence of the NTIS and its association with outcome in medical intensive care units (ICUs) are missing. Complete thyroid hormone levels from 247 of 743 patients admitted to our ICU between October 2002 and February 2004 were retrospectively evaluated. From these patients, Acute Physiology and Chronic Health II scores, ICU mortality, length of stay, mechanical ventilation, and concomitant medication were recorded. Ninety-seven patients (44.1%) had low FT(3) levels indicating an NTIS, either with normal (23.6%) or reduced (20.5%) serum thyrotropin levels. Of 97 patients with NTIS, 24 (23.3%) also showed reduced serum FT(4) levels. The NTIS was significantly associated with Acute Physiology and Chronic Health II scores, mortality, length of stay, and mechanical ventilation. In a multivariate Cox regression analysis, the combination of low FT(3) and low FT(4) was an independent risk factor for survival. Nonthyroidal illness syndrome is frequent at a medical ICU. A reduction of FT(4) together with FT(3) is associated with an increase in mortality and might reflect a maladaptive process, thereby worsening the disease.

Perioperative management of patients with hypothyroidism

Hypothyroidism is a common disorder affecting the cardiovascular, respiratory, hematopoietic, and renal organ systems--each of which is particularly germane in the management of the surgical patient. In general, treatment of recognized hypothyroidism is recommended before any surgical procedure whenever possible and euthyroidism should be documented by measurement of serum TSH as part of the preoperative evaluation. Such a strategy is likely to result in better surgical outcomes with improved morbidity and mortality. One exception to treating first with thyroid hormone is the patient with angina or coronary artery disease requiring bypass grafting, angioplasty or stenting. In this setting, preoperative thyroid hormone therapy could tax the ischemic myocardium. The coronary blood flow should be addressed first, and thyroid hormone therapy initiated afterwards. The authors have emphasized the need for caution in the interpretation of low serum thyroid hormones in sick or surgical patients because of the importance of distinguishing between hypothyroidism and the "euthyroid sick syndrome." There is no clear evidence at this point to support thyroid hormone replacement in the latter patients, and it may be potentially harmful. Rather, we hold that T3 treatment of various surgical and other patients with nonthyroidal illness should be deferred until proof of its therapeutic efficacy is demonstrated.

Heart failure accompanied by sick euthyroid syndrome and exercise training

Sick euthyroid syndrome is defined as the decrease of serum free triiodothyronine with normal free L-thyroxin and thyrotropin. Its appearance in patients with chronic heart failure is an indicator of severity. Exercise training through a wide variety of mechanisms reverses sick euthyroid syndrome (normalization of free triiodothyronine levels) and improves the ability to exercise. There is a connection during exercise among dyspnea, hyperventilation, fatigue, catecholamines, a decrease in the number and function of beta-blocker receptors, and elevation of serum free triiodothyronine. It is not known whether sick euthyroid syndrome contributes to the development of heart failure or is only an attendant syndrome.

[Diagnosis and therapy of patients with euthyroid goiter]

Nontoxic goitre is common, even in areas where iodine intake is sufficient. The most important symptoms and signs of nontoxic goitre are caused by compression of vital structures in the neck or upper thoracic cavity. In any patient with goitre the serum concentration of thyroid-stimulating hormone (TSH) should be measured to detect or exclude clinically inapparent (subclinical) hyper- or hypothyroidism. CT and MRI are expensive but very sensitive methods to identify tracheal compression and to determine intrathoracic extension. Thyroid ultrasonography and scintigraphy are not routinely indicated. Fine-needle aspiration biopsy is indicated in patients with fast-growing nodules and nodules that have a firmer consistency than other nodules within the gland. Thyroidectomy is standard therapy for young and otherwise healthy patients, especially when prompt decompression of vital structures is required. Radioiodine therapy is an attractive alternative to surgery in older patients, in those with cardiopulmonary disease, and in those with recurrent goitre. Thyroxin therapy may be tried in young patients with small, diffuse goitres who have normal serum TSH concentrations.

Sick euthyroid syndrome. What to do when thyroid function tests are abnormal in critically ill patients

Abnormal thyroid hormone concentrations are common in patients with serious nonthyroidal illnesses. Early evidence suggests that thyroid hormone levels may predict the prognosis for some patients. Abnormal thyroid function is usually reversible, but thyroid function tests should be repeated when the nonthyroidal illness is resolved. Whether active intervention using thyroid hormone supplements is beneficial or not remains controversial and requires future large-scale investigation.

Clinical review 86: Euthyroid sick syndrome: is it a misnomer?

Alterations in thyroid function tests are very common in patients with NTI. Multiple, complex, and incompletely understood mechanisms are involved in these abnormalities. Knowledge of these abnormalities is necessary to avoid errors in the diagnosis of thyroid disease. Measurement of serum TSH, free T4, and free T3 levels by direct equilibrium dialysis/RIA methods probably yield most useful (accurate) information in the setting of NTI. Patients with low free T4 by these methods and normal or low TSH have secondary hypothyroidism. This may be due to NTI per se, drugs administered for treatment of NTI, or associated pituitary or hypothalamic disease; the latter consideration may require evaluation of cortisol reserve, PRL, and/or gonadotropins. A serum TSH level above 20-25 microU/mL probably reflects primary hypothyroidism; accompanying findings of goiter, low free T4, and positive antithyroid antibodies help establish the diagnosis. An elevated serum concentration of rT3 argues against hypothyroidism. Studies have demonstrated no discernible benefit of treatment of NTI patients with T4. Some studies have shown a few benefits of treatment with T3 in selected cases, but much more needs to be learned. There is no evidence of harm by treatment of NTI patients with up to replacement doses of T3. As some NTI patients may indeed be hypothyroid, the term ESS should be replaced with NTIS.

Euthyroid sick syndrome: an overview

Abnormalities of thyroid hormone concentrations are seen commonly in a wide variety of nonthyroidal illnesses, resulting in low triiodothyronine, total thyroxine, and thyroid stimulating hormone concentrations. These thyroid hormone changes may be mediated in part by cytokines or other inflammatory mediators, acting at the level of the hypothalamus and pituitary, the thyroid gland, and the hepatic deiodinase system, as well as on binding of thyroxine to thyroid binding globulin. The degree of thyroid function disturbance correlates with disease severity and low levels of thyroid hormones predict a poor prognosis in several illnesses. It remains unresolved whether the hormone responses in the euthyroid sick syndrome represent part of an adaptive response, which lowers tissue energy requirements in the face of systemic illness, or a maladaptive response, which induces damaging tissue hypothyroidism. Consequently, the use of thyroid hormone therapy in the euthyroid sick syndrome is controversial. The small number of controlled trials performed to date have shown conflicting results on the cardiovascular effects of triiodothyronine, and none has had the statistical power to address the question of altered mortality. Future trials of therapy should concentrate on patients with severe nonthyroidal illness and a high mortality rate. Meanwhile, better understanding is needed of the impact of the altered thyroid hormone status on tissue function.

[Ultrasound-guided alcohol instillation in treatment of autonomous thyroid adenoma]

In 16 patients with unifocal thyroid autonomy suffering from hyperthyroidism and in 2 patients and euthyrosis 2-4 ml 96% alcohol was instilled to destroy the autonomous thyroid tissue while permanently monitoring the procedure by means of sonography. 17 of the patients were suffering from struma nodosa. Localization of the focally autonomous adenoma was possible, together with differentiation against concomitant thyroid nodes with normal or reduced function, by coinciding the findings obtained via colour Doppler sonography and scintiscanning. In one female patient local pain occurred during instillation that had to be alleviated by means of analgetics; there were no other noticeable side effects. 12 of 16 patients suffering from hyperthyroidism were euthyrotic 5 weeks after the first alcohol instillation; the thyrostatic dose had to be reduced in 4 patients. B-image sonography showed a reduction in size of the instilled adenomas and echo-poor and partly cystic transformation. Colour Doppler sonography revealed a marked reduction of internal vascularisation with preserved marginal vessels. Scintiscan control no longer visualised the autonomic foci (n = 10) or only with reduced activity (n = 7). Sonographically monitored on-target instillation of alcohol into autonomic thyroid adenoma is an effective, low-risk and low-cost procedure that can also be applied to outpatients by physicians well-versed in colour Doppler sonography and sonographic puncture technique. Colour Doppler sonographic localization of autonomic foci is methodically mandatory in patients suffering from struma multinodosa.

Comparative pharmacology of the thyroid hormones

The thyroid hormones tetraiodothyronine and triiodothyronine (T3) are involved in a variety of biologic mechanisms. Thyroid hormones regulate protein, lipid, and carbohydrate anabolism and improve oxygen consumption in almost all body tissues. Thyroid hormone is formed by coupling of iodinated tyrosine molecules in the thyroid gland. Tetraiodothyronine is converted to T3, the active thyroid hormone. Drugs, disease states that induce severe physiologic stress, and surgical conditions (eg, cardiopulmonary bypass) can alter the levels of circulating active hormone by interfering with the peripheral conversion of tetraiodothyronine to T3. This low T3 ("euthyroid sick syndrome") state is manifested by low circulating levels of T3 and hemodynamic abnormalities. Active thyroid hormone replacement with T3, because of its pharmacologic actions, may be an ideal therapy in these conditions.

The aging thyroid in health and disease

The most consistent biochemical thyroid abnormality associated with age, various illnesses, and drugs is the low T3 syndrome due to decreased activity of 5'-deiodinase. Lower T3 levels may help reduce the catabolic effects of illness on the individual. The diagnosis of hypothyroidism can be missed in the elderly when its typical manifestations are attributed to aging. The diagnosis of hyperthyroidism in the elderly may likewise be difficult because of atypical clinical presentations. A high index of clinical suspicion should lead to a timely diagnosis of these eminently treatable disorders.