THE THYROID FUNCTION IN YOUNG MEN DURING PROLONGED EXERCISE AND THE EFFECT OF ENERGY AND SLEEP DEPRIVATION

Thyroid function has been investigated in 24 young military cadets participating in a 5 d ranger training course with heavy physical exercise, calorie deficiency and deprivation of sleep. The cadets were divided into three groups, each differing in the amount of sleep and food consumption. The serum levels of thyroid hormones (T4, FT4, T3, rT3) and TBG showed a biphasic pattern during the course. Initially there was an increased secretion concomitant with an increased deiodination of T4 to T3 and rT3 mainly due to physical exercise. When the activities lasted for several days without sufficient food supply the thyroid secretion decreased simultaneously with an alteration of the peripheral conversion of T4 to rT3 instead of T3. A significant correlation was found between the changes in total and free thyroxine (r = 0.9) and between the increase in rT3 and decrease in T3 (r = 0.6). TSH decreased during the first day of activities and remained low throughout the course. The TSH response to TRH stimulation was greatly reduced during the course due to physical exercise and calorie deficiency. The present investigation demonstrates that the thyroid function is strongly affected by prolonged physical exercise and a negative energy balance, whereas sleep deprivation does not have any significant influence. The results indicate that the alteration observed is not regulated just by the hypothalamo-pituitary-thyroid-axis alone.     

Thyroid gland volume and thyroid function during and after acute hepatitis infection

Thyroid function, the occurrence of goiter, and ultrasonically determined thyroid gland volume were investigated in 23 consecutive nonalcoholic patients with acute viral hepatitis during and six months after recovery, and compared with data obtained from 23 matched controls. Seven patients had clinically detectable goiter during disease, but only one after recovery (P less than 0.05). Median thyroid volume was 28 mL (range 15 to 42 mL) compared with 18 mL (range 12 to 27 mL) after recovery (P less than 0.001), and 17 mL (range 11 to 24 mL) in the controls (P less than 0.001). During acute hepatitis, serum levels of thyroxine, thyroxine binding globulin, and free thyroxine index were significantly increased while triiodothyronine and thyrotropin levels were unaltered and triiodothyronine resin uptake and free triiodothyronine index levels were decreased. After recovery all thyroid variables were normalized. In conclusion, acute liver disease was associated with a marked increase in thyroid volume, but the study did not clarify the mechanism underlying thyroid enlargement.     

Change in serum thyroid hormone levels in patients with acute myocardial infarction

It has been reported that there is a decrease in the serum concentration of thyroid hormones in non-thyroidal illness. In the present study we made serial measurements of serum concentration of thyroid hormones [triiodothyronine (T3), thyroxine (T4), free triiodothyronine (FT3), free thyroxine (FT4), reverse triiodothyronine (rT3)], thyroid stimulating hormone (TSH) and thyroxine binding globulin (TBG) in 10 patients with acute myocardial infarction (AMI, Grade I, according to the classification of Killip & Forrester) during 14 days after onset. In the early phase of AMI, serum T3, T4, FT3 and FT4 levels decreased while rT3 increased. TSH and TBG levels, however, were unchanged. In the patients with a high peak creatine phosphokinase activity (greater than or equal to 400 mU/ml), the decrease in thyroid hormone and increase in serum rT3 levels were greater than in patients with a low peak value (less than 400 mU/ml), suggesting a correlation between severity of AMI and changes in serum thyroid hormone levels. Especially, serum FT3 levels fell below the lower limit of controls within 14 days, with the lowest levels and the rT3 peak on the third day after onset. These data suggest that in AMI peripheral conversion of T4 favours rT3 production and that low levels of serum FT3 and T3 protect the infarcted heart muscle against thyroid hormone action.     

Rapid down-regulation of thyroid hormones in acute myocardial infarction: is it cardioprotective in patients with angina?

BACKGROUND: In severe illness of any cause, down-regulation of the thyroid hormone system may occur. How this affects patients with acute myocardial infarction (AMI) is largely unknown. OBJECTIVE: To investigate changes in serum levels of the thyroid hormones during AMI and their association with cardiac function and outcome. METHODS: Forty-seven consecutive euthyroid patients with AMI were studied prospectively during the first 5 days and again 6 and 12 weeks later. Time from pain onset was used in all analyses. RESULTS: The thyroid hormone system was rapidly down-regulated with maximal changes 24 to 36 hours after onset of symptoms. The mean level of the hormone total triiodothyronine (T3) decreased 19% (P =.02), the inactive metabolite reverse T3 (rT3) levels increased 22% (P =.01), and thyrotropin levels declined 51% (P<.001) between the first 6-hour and the 24- to 36-hour period. The prohormone free thyroxine was largely unchanged. Patients with poor heart function or more intense inflammatory reaction showed more pronounced down-regulation of the thyroid system. No correlation was found with cardiac enzymes. Patients with prior angina pectoris had lower T(3) levels in early samples, smaller infarctions, and higher levels of C-reactive protein and the proinflammatory cytokine interleukin 6 on admittance. Peak levels of interleukin 6 correlated negatively with T3 (P =.005) and positively with rT3 (P<.05), suggesting that down-regulation before AMI may be cardioprotective. However, mortality was high among patients with the most pronounced thyroid level depression, indicating that down-regulation after AMI may be maladaptive. CONCLUSIONS: The thyroid hormone system is rapidly down-regulated in AMI. This may be beneficial during acute ischemia. Patients with angina had higher levels of interleukin 6 and C-reactive protein and more depressed thyroid hormone system in early samples. Thyroid level depression in patients with angina may possibly have been present before the infarction process started. This novel finding needs further evaluation in large studies to sort out cause-and-effect relationships.     

Thyroid function after autologous bone marrow transplantation.

Thyroid function was prospectively analysed in 111 consecutive patients in relation to autologous bone marrow transplantation (ABMT). Median follow-up time was 12 (range 3-60) months. As part of the conditioning treatment 58 patients had received total body irradiation (TBI) as a single dose of 7.5 Gy (dose rate 0.15 Gy/min). Thyroxine, triiodothyronine, thyrotropin (TSH) and thyroid antibodies were analysed before ABMT, every third month during the first year afterwards and then once annually. Thyroid dysfunction was seen in 20 patients (after TBI in 16, after non-TBI treatments in four). Five of these, all treated with TBI, developed primary hypothyroidism and in 15 compensated hypothyrosis, transient in eight (40%), was seen. There was a highly significant (p less than 0.001) increase, within the normal range, in median TSH level, prior to ABMT compared with 1 year following ABMT. In patients who developed thyroid dysfunction, the TSH level before ABMT was significantly higher (p less than 0.001) than in those who remained euthyroid. In four patients persistent elevated thyroid antibody titers appeared and in two of them hypothyrosis developed. No correlation between thyroid dysfunction and age was noted. The findings are similar to those after allogeneic BMT described by others.     

Thyroid hormones and lipolysis in physically trained rats

In rats a single bout of exercise resulted in increased triiodothyronine (T3), thyroxine (T4), and triiodothyronine/reverse triiodothyronine ($\text{T3}\text{rT3}$) ratio 20 hr after exercise. The effect of norepinephrine on lipolysis in vitro was potentiated.In trained rats no changes were found in T4, T3 or rT3 concentrations. The $\text{T3}\text{rT3}$ ratio as well as basal and stimulated TSH concentrations decreased in comparison with sedentary, freely eating rats. Moderate food restriction to produce a body weight similar to that of trained animals caused no changes in T4, T3 or rT3 concentrations but caused a decrease in $\text{T3}\text{rT3}$ and in TSH levels. Training and moderate food restriction groups were not different. T3 in vitro caused a potentiation of catecholamine induced lipolysis in trained and food-restricted animals. With aging the serum concentration of T3 decreased and that of rT3 increased.Acute and chronic exercise both exert an effect on peripheral hormonal responses of lipolysis, while they have different and opposite effects on thyroid hormone concentrations. Physical training seems to have effects in this regard similar to those of moderate energy intake restriction. The results suggest that changes in peripheral effects of thyroid hormones during training should attract more attention.     

Relationship between thyroid volume and serum thyroglobulin during long-term suppression with triiodothyronine in patients with diffuse non-toxic goitre

Twenty-five patients with non-toxic diffuse goitre were studied during and after 12 months of treatment with 60 micrograms triiodothyronine daily in order to see whether a correlation could be found between the reductions of thyroid volume, using ultrasonic scanning, and serum thyroglobulin. Thyroid function tests and thyroid volume determination were performed before treatment and after 3, 6 and 12 months of therapy in 19 patients (group 1). In patients of group 2 (n = 19) the same tests were performed at the end of 12 months treatment and 6 and 12 months after withdrawal. Before treatment all patients had a significantly increased thyroid volume compared to controls matched according to sex, age and body weight (P less than 0.001). Serum thyroglobulin was elevated compared to controls (P less than 0.02), with a significantly positive correlation to the thyroid volume (Spearmann's Rho = 0.52, P less than 0.02). Both serum thyroglobulin and thyroid volume decreased during treatment in the majority of the patients, concomitantly in approximately half of them. After withdrawal of treatment (group 2) serum thyroglobulin showed a median increase of 54% after 6 months and remained unchanged thereafter, whereas the thyroid volume was unchanged after 6 months. These findings might support the concept that the regulation of thyroid growth and of protein synthesis and degradation might be determined by different factors.     

THYROID HORMONES IN ACUTE MYOCARDIAL INFARCTION

Thyroid hormones were serially measured over a 2-week period in thirty-four consecutive patients with acute myocardial infarction (AMI). A transient increase in plasma rT3 and a decrease in plasma T3 was found, with the maximum changes occurring on the third day after the onset of AMI. The changes in plasma rT3 and T3 were greater in the seventeen patients with a complicated AMI (mean peak SGOT 145 u/l) than in the seventeen patients with an uncomplicated AMI (mean peak SGOT 79 u/l). A correlation was found between infarct size (as estimated by the peak SGOT value) and the following indices: ΔrT3, ΔT3, highest rT3/T3 and highest rT3/T4 ratios. A transient increase in plasma TSH (peak on days 4 and 5) and in plasma T4 and FT4 index (peak on days 6 and 7) was also observed, whereas T3 resin uptake (T3U) decreased. These findings suggest that the following sequence of events occurs in thyroid hormone metabolism during AMI: (1) inhibition of the 5′-deiodination of T4, resulting in increased plasma rT3 and decreased plasma T3 values, and in a lower metabolic clearance of T4. (2) Increased secretion of TSH (provoked by the lower T3 levels) resulting in increased thyroidal secretion of T4 and T3, which is then switched off by the negative feedback of thyroid hormones on the pituitary.     

Effects of thyroid hormones on serum levels of adipokines as studied in patients with differentiated thyroid carcinoma during thyroxine withdrawal.

OBJECTIVE: Previous studies addressing the influence of thyroid hormones on serum levels of adipokines yielded conflicting results. We aimed to study the impact of short-term overt hypothyroidism on serum leptin, resistin, and adiponectin levels in an in vivo human model. DESIGN: Twenty-two women with differentiated thyroid carcinoma were studied the last day of their thyroxine-suppressive treatment, 4-7 days after withdrawal, and the day before whole-body scanning. Evaluations included serum thyroid hormone, leptin, resistin, and adiponectin concentrations, fasting glucose and insulin, lipid profiles, body temperature, body mass index, and total body fat mass. MAIN OUTCOMES: Thyroid function changed from subclinical or mild hyperthyroidism to normal free thyroxine and triiodothyronine levels, ending in overt hypothyroidism. Thyroxine withdrawal resulted in an increase in serum resistin (p = 0.007) and leptin (p = 0.006) concentrations, whereas adiponectin levels remain unchanged. A significant decrease in body temperature during thyroxine withdrawal was paralleled by a decrease in fasting glucose (p = 0.006) and insulin resistance (p = 0.033), which occurred despite an increase in estimated total body fat mass. CONCLUSION: Thyroid hormones are important regulators of energy balance and intermediate metabolism, influencing the serum concentrations of leptin and resistin.     

Acute exercise increases systemic arterial compliance after 6-month exercise training in older women.

High physical activity or aerobic exercise training increases central arterial distensibility in older humans. However, the effect of a single bout of exercise on central arterial distensibility in older humans is unknown. Furthermore, the effect of exercise training on central arterial distensibility during exercise is unclear. We investigated whether systemic arterial compliance (SAC) changes after acute exercise in older humans, and, if so, whether this change in SAC is enhanced by aerobic exercise training. Seven untrained older women (61-69 years old) participated in a 6-month exercise intervention study. We measured SAC after acute exercise (cycling exercise at 80% of their individual ventilatory threshold for 30 min) before and after 6 months of aerobic exercise training. After exercise training, the individual ventilatory threshold was significantly increased. In addition, both the SAC at rest and that 30 min after acute exercise were significantly increased after the exercise training program. Before exercise training, there was no significant increase in SAC after acute exercise, whereas, after exercise training, the SAC was significantly increased 30 min after acute exercise. The present study suggests that, after aerobic exercise training, SAC increases after acute exercise in older humans, and that the SAC at rest and after acute exercise is enhanced by aerobic exercise training, thereby causing an effective adaptation in increase in cardiac output during exercise.     

Thyroid hormone deficiency and postmenopausal status independently increase serum osteoprotegerin concentrations in women

OBJECTIVE: To study the impact of thyroxine (T4) withdrawal on serum osteoprotegerin concentrations in women, using a healthy euthyroid control group matched for age and postmenopausal status as reference. Subjects and design: Nineteen women with differentiated thyroid carcinoma were studied the last day on T4 suppressive treatment, 4-7 days after withdrawal and the day before whole body scanning. Eighteen women matched for age and postmenopausal status served as controls. Serum thyroid hormones, urinary bone markers and serum osteoprotegerin concentrations were measured. Statistical methods included repeated measures analysis of variance and one-way analysis of variance. RESULTS: Patients progressed from subclinical or mild hyperthyroidism at baseline to normal free T4 and triiodothyronine levels 4-7 days later, ending in overt hypothyroidism before scanning. Serum osteoprotegerin increased, and urinary deoxypyridolines/creatinine and pyridolines/creatinine ratios decreased, with acute hypothyroidism (P = 0.026, P = 0.003, and P < 0.001 respectively). Urinary deoxypyridolines/creatinine ratio, pyridolines/creatinine ratio, and serum osteocalcin during hypothyroidism were lower compared with those of healthy controls (P = 0.023, P = 0.019, and P = 0.011 respectively). Serum osteoprotegerin concentrations were higher in postmenopausal patients when compared with premenopausal ones, irrespective of the changes in thyroid function (P = 0.001). CONCLUSION: Serum osteoprotegerin concentrations increase following acute hypothyroidism after T4 withdrawal in women with differentiated thyroid carcinoma, and also with postmenopausal status.     

Relationship between exercise capacity and brain natriuretic peptide in patients after cardiac surgery

OBJECTIVES: Physical training in cardiac patients can increase exercise capacity and reduce plasma brain natriuretic peptide(BNP) concentration, but these effects may depend on the etiology of cardiac disease. The change in exercise capacity and BNP during the training period were investigated in patients with different cardiac diseases. METHODS: Ninety-one patients after coronary artery bypass grafting(CABG) and 78 patients after valve replacement (VR) underwent a symptom-limited incremental cardiopulmonary exercise test before (1 month) and 6 months after physical training. Anaerobic threshold and peak oxygen uptake(peak-Vo2) were measured during the cardiopulmonary exercise test. Before each cardiopulmonary exercise test, a blood sample was obtained in the resting condition for measuring BNP. RESULTS: Anaerobic threshold and peak-Vo2 were increased significantly from 1 month to 6 months in both groups. BNP in the CABG group indicated a tendency to decrease (194.6 +/- 155.3-->144.2 +/- 232.2 pg/ml, p < 0.1) from 1 month to 6 months. BNP in VR group was significantly decreased (159. 9 +/- 115.5-->112.8 +/- 131.7 pg/ml, p < 0.05) during the training period. The CABG group showed a significant negative correlation between peak-Vo2 and BNP at 1 month(r = -0.28, p < 0.01) and at 6 months(r = -0.39, p = 0.001). The VR group showed a significant negative correlation between peak-Vo2 and BNP at 6 months(r = -0.32, p < 0.01), but not at 1 month. CONCLUSIONS: Six months of physical training in patients after cardiac surgery may improve exercise capacity and reduce BNP. BNP concentration in the VR group before physical training did not reflect functional capacity.     

Serum thyrotropin by ultrasensitive immunoradiometric assay and serum free thyroid hormones in pregnancy

Variations of serum TSH, measured by an ultrasensitive immunoradiometric assay, of serum total and free thyroid hormones and of thyroxine-binding globulin (TBG) and sex hormone-binding globulin (SHBG) were investigated in a group of 18 normal women before and during pregnancy. A gradual increase of total thyroid hormones, TBG and SHBG was observed, while mean serum free thyroxine and free triiodothyronine progressively decreased. Serum TSH concentrations were comprised within the normal range throughout pregnancy, although a small but significant increase was found in the 2nd and 3rd trimester. These changes may represent a compensatory mechanism to meet the increased demand for thyroid hormones in pregnancy and must be taken into account for a correct evaluation of thyroid function during gestation.     

The role of thyroid hormones in acute coronary syndromes: Prognostic value of alterations in thyroid hormones

The prognosis of acute coronary syndromes (ACS ) is affected by many factors. Normal thyroid homeostasis is known to alter during various critical illnesses, a condition that has been shown to correlate with the severity of the disease and increased mortality. The purpose of this article is to review literature to emphasize the considerable association of thyroid function with the cardiovascular system and summarize all existing evidence with regard to the role of thyroid hormones alterations during ACS . The electronic databases of PubMed , Medline, Scopus, and Cochrane were searched for relevant literature and studies. Alterations in thyroid hormone plasma concentrations, especially low triiodothyronine (T3 ) levels, represent a hormonal imbalance that is not uncommon among patients suffering an acute coronary event. Many studies have identified this abnormal thyroid hormonal status to be related to worse prognosis. Although further large‐scale clinical trials are needed, the low T3 syndrome manifesting in patients during ACS might be useful in prognostic stratification.     

The role of thyroid hormones in the control of energy expenditure

Thyroid hormones have a direct effect on the basal or resting metabolic rate in man and a permissive effect on the adaptive thermogenesis of small animals, while altering the energy expended in exercise to the extent that patients with thyroid disorders exercise to a greater or lesser degree. The physiological concepts of energy expenditure need to be seen in the context of a new method for measuring 'thyroid thermogenesis'. Thyroid hormones seem, in evolutionary terms, to have developed a thermogenic role during the transition from poikilothermy to homeothermy; they are responsible for the increased heat production required for homeotherms to maintain body temperature above that of the environment. The potential mechanisms responsible for thyroid hormone-controlled energy expenditure are complex. Uncoupled oxidative phosphorylation is probably not responsible for thyroid hormone-controlled thermogenesis except in the special case of brown adipose tissue thermogenesis, where thyroid hormones act permissively. The concept that increased ATP generation must be coupled to ATP utilization needs to be linked with the idea that thyroid hormone-controlled thermogenesis must be through inefficient pathways of metabolism. Several of these potentially important pathways of intermediary metabolism in thyroid hormone-controlled thermogenesis can now be defined and measured, but their role in the regulation of nutritionally induced alterations in thyroid status and thermogenesis remains to be explored.     

Developmental changes of plasma inhibin, gonadotropins, steroid hormones, and thyroid hormones in male and female Shao ducks

Plasma samples from developing male and female Shao ducks were assayed for immunoreactive (ir-) inhibin, follicle-stimulating hormone (FSH), luteinizing hormone (LH), steroid hormones, and thyroid hormones. In the male, plasma ir-inhibin significantly increased between 75 and 155 days posthatch, and then decreased slightly at day 165. Plasma FSH of male ducks decreased from day 35 to day 55, followed by progressive elevation until day 95. Plasma FSH of male ducks fell significantly at days 135 and 165, while plasma ir-inhibin rose to high level. In female ducks, plasma ir-inhibin remained low until the start of lay, and thereafter significantly increased at day 135. Plasma FSH fluctuated before day 95 and significantly rose at day 115, and decreased thereafter. In males, plasma LH did not vary significantly before day 135, however, plasma testosterone significantly increased from day 95 onwards. No changes in plasma LH were observed during development of female ducks. Plasma estradiol-17beta gradually increased reaching a peak level at day 135. Plasma progesterone did not vary significantly before day 135 and thereafter significantly increased. Both sexes showed a similar pattern in changes of plasma thyroid hormones during sexual development. There was a significant increase in plasma thyroxine (T4) at day 95, thereafter decreased. Plasma triiodothyronine (T3) was at high level at the earlier stage of development and significantly decreased at day 55. Significant increase in plasma T3 in male and female ducks was observed at 135 and 115 days, respectively. In conclusion, these results demonstrated that the rise in inhibin is correlated with age of sexual maturity in the female while the rise in inhibin significantly precedes sexual maturity in the male. There was a progressive increase in plasma steroid hormones towards sexual maturity, and there was no sex difference in the time course of thyroid hormones.     

Echocardiographic and electrocardiographic measures in obese children after an exercise program

The influence of an exercise training on anthropometric changes and cardiac dimensions was studied in 18 obese children (age 10 to 11 years). Eighteen obese children participated in a jogging program, 5 days/week, for 1 or 2 years and 15 normal weight children (age 10 to 11 years) in the control group participating in their regular physical education class. Anthropometric measurements, echocardiograms and electrocardiograms were obtained before and after the exercise programs. The weight, degree of obesity and resting heart rate had decreased after 1 year of the exercise training. Left ventricular end-diastolic dimension increased after 1 year of the exercise training. Left ventricular wall thickness did not change. The total voltage in SV1 + RV5 decreased after 3 months of the exercise training but returned to pre-training voltage after 1 year of training. There was no change after 2 years of training. In conclusion, 1 year of exercise in obese children decreased resting heart rate and increased left ventricular end-diastolic dimension and left ventricular mass.     

Delayed effects of prolonged exercise on serum lipoproteins

The delayed lipoprotein changes after a 3-hour running test were examined in 14 moderately trained young male subjects. Fasting blood samples were obtained one day before, immediately before, and one, two, and four days after the race. Nonfasting samples were collected immediately after, one, and three hours after exercise. Three hours after the race, the ratio of unesterified cholesterol to cholesteryl esters was significantly increased, and one and two days after the race it was significantly decreased compared to the preexercise value. The HDL2/HDL3 ratio, measured by density-gradient ultracentrifugation was one and three hours after the running significantly elevated. However, no redistribution of the HDL2/HDL3 cholesterol ratio determined by a precipitation method with polyanions was found at this time. One day postexercise HDL cholesterol rose significantly above the preexercise value, and this was associated with an elevation of the HDL3 subfraction. On the following day a significant increase of HDL2 cholesterol and the HDL2/HDL3 cholesterol ratio was found. The apolipoproteins A-I, A-II, and B, measured by radial immunodiffusion, did not change during the first hours and the first two days after the race. On the second postexercise day the Lp(a) lipoprotein rose significantly above the preexercise value. Compared with the preexercise level the LCAT activity was significantly elevated three hours after the race and significantly decreased two days later. The present study suggests that during the first few days after prolonged exercise a number of plasma lipoprotein changes take place that are similar to those observed after a period of physical training.     

Thyroid hormone receptors in brain development and function

Thyroid hormones are important during development of the mammalian brain, acting on migration and differentiation of neural cells, synaptogenesis, and myelination. The actions of thyroid hormones are mediated through nuclear thyroid hormone receptors (TRs) and regulation of gene expression. The purpose of this article is to review the role of TRs in brain maturation. In developing humans maternal and fetal thyroid glands provide thyroid hormones to the fetal brain, but the timing of receptor ontogeny agrees with clinical data on the importance of the maternal thyroid gland before midgestation. Several TR isoforms, which are encoded by the THRA and THRB genes, are expressed in the brain, with the most common being TRalpha1. Deletion of TRalpha1 in rodents is not, however, equivalent to hormone deprivation and, paradoxically, even prevents the effects of hypothyroidism. Unliganded receptor activity is, therefore, probably an important factor in causing the harmful effects of hypothyroidism. Accordingly, expression of a mutant receptor with impaired triiodothyronine (T(3)) binding and dominant negative activity affected cerebellar development and motor performance. TRs are also involved in adult brain function. TRalpha1 deletion, or expression of a dominant negative mutant receptor, induces consistent behavioral changes in adult mice, leading to severe anxiety and morphological changes in the hippocampus.     

Effect of ultrasound-guided interstitial laser photocoagulation on benign solitary solid cold thyroid nodules - a randomised study

AIM: To evaluate the efficacy of ultrasound (US)-guided interstitial laser photocoagulation (ILP) on thyroid function, nodule size and patient satisfaction in benign solitary solid cold thyroid nodules by comparing one ILP session with no treatment in a prospective randomised study. MATERIALS AND METHODS: Thirty euthyroid outpatients with a benign solitary solid and a scintigraphically cold thyroid nodule causing local discomfort were assigned to one session of ILP (n = 15) or observation (n = 15) and followed for 6 months. Thyroid nodule volume and total thyroid volume were assessed by US and thyroid function was determined by routine assays before and during follow-up. Pressure and cosmetic complaints before and at 6 months were evaluated on a visual analogue scale. ILP was performed under US guidance and with an output power of 2.5-3.5 W. RESULTS: In the ILP group, the nodule volume decreased from 8.2 ml (6.1; 11.9) (median; quartiles) to 4.8 ml (3.0; 6.6) after 6 months (P = 0.001). The overall median reduction was 44% (37; 52), which correlated with a significant decrease in pressure symptoms as well as cosmetic complaints. In the control group, a non-significant increase in median nodule volume of 7% (0; 34) after 6 months was seen. No major side-effects were seen in the ILP group. There was no correlation between thermal energy deposition and nodule volume reduction. Thyroid function was unaltered throughout. CONCLUSION: US-guided ILP, given as a single treatment, resulted in a satisfactory clinical response in the majority of patients with a benign solitary solid cold thyroid nodule, and may become a clinically relevant alternative to surgery in selected patients.