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PubMed2001

Measurement of serum concentrations of free thyroxine, total thyroxine, and total triiodothyronine in cats with hyperthyroidism and cats with nonthyroidal disease.

OBJECTIVE: To determine the usefulness of measuring serum free thyroxine (T4) concentration as a diagnostic test for hyperthyroidism in cats, and to determine the influence of nonthyroidal disease on free T4 concentration in cats without hyperthyroidism. DESIGN: Prospective case series. ANIMALS: 917 cats with untreated hyperthyroidism, 221 cats with nonthyroidal disease, and 172 clinically normal cats. PROCEDURE: Serum free T4, total T4, and total triiodothyronine (T3) concentrations were measured in cats with untreated hyperthyroidism and cats with nonthyroidal disease. Serum total T4 and T3 concentrations were determined by use of radioimmunoassay, and free T4 concentration was measured by use of direct equilibrium dialysis. Reference ranges for hormone concentrations were established on the basis of results from the 172 clinically normal cats. RESULTS: Sensitivity of serum free T4 concentration as a diagnostic test for hyperthyroidism was significantly higher than the test sensitivity of either total T4 or T3 concentration. Of the 221 cats with nonthyroidal disease, 14 had a high free T4 concentration (ie, false-positive result). Therefore, calculated specificity of measuring serum free T4 concentration as a diagnostic test for hyperthyroidism was significantly lower than test specificity of measuring either the total T4 or T3 concentration. CONCLUSIONS AND CLINICAL RELEVANCE: Results indicate that determination of free T4 concentration is useful in the diagnosis of hyperthyroidism, especially in cats in which hyperthyroidism is suspected but total T4 and T3 concentrations are within reference ranges. However, because some cats with nonthyroidal disease have high serum free T4 concentrations, hyperthyroidism should not be diagnosed solely on the finding of high free T4 concentration.

Animals↗
PubMedDate not supplied

Effects of methimazole on renal function in cats with hyperthyroidism.

The purpose of this study was to investigate the effects of methimazole on renal function in cats with hyperthyroidism. Twelve cats with naturally occurring hyperthyroidism and 10 clinically normal (i.e., control) cats were included in this study. All cats initially were evaluated with a history, physical examination, complete blood count, serum biochemistry profile, basal serum total thyroxine concentration, complete urinalysis, and urine bacterial culture. Glomerular filtration rate (GFR) was estimated by a plasma iohexol clearance (PIC) test. After initial evaluation, hyperthyroid cats were treated with methimazole until euthyroidism was achieved. Both groups of cats were then reevaluated by repeating the initial tests four to six weeks later. The mean (+/-standard deviation) pretreatment estimated GFR for the hyperthyroid cats was significantly higher (3.83+/-1.82 ml/kg per min) than that of the control cats (1.83+/-0.56 ml/kg per min). Control of the hyperthyroidism resulted in a significantly decreased mean GFR of 2.02+/-0.81 ml/kg per minute when compared to pretreatment values. In the hyperthyroid group, the mean increases in serum urea nitrogen (SUN) and creatinine concentrations and the mean decrease in the urine specific gravity after treatment were not statistically significant when compared to pretreatment values. Two of the 12 hyperthyroid cats developed abnormally high serum creatinine concentrations following treatment. These results provide evidence that cats with hyperthyroidism have increased GFR compared to normal cats, and that treatment of feline hyperthyroidism with methimazole results in decreased GFR.

Animals↗
PubMed1999

Serum fructosamine concentration in cats with overt hyperthyroidism.

OBJECTIVE: To determine the effect of hyperthyroidism on serum fructosamine concentration in cats. DESIGN: Cohort study. ANIMALS: 22 cats with overt hyperthyroidism. PROCEDURE: Hyperthyroidism was diagnosed on the basis of clinical signs, detection of a palpable thyroid gland, and high total serum thyroxine (T4) concentrations. Hyperthyroid cats with abnormal serum albumin, total protein, and glucose concentrations were excluded from the study. Samples for determination of serum fructosamine concentration were obtained prior to initiating treatment. Results were compared with fructosamine concentrations in healthy cats, cats in which diabetes had recently been diagnosed, and cats with hypoproteinemia. In 6 cats, follow-up measurements were obtained 2 and 6 weeks after initiating treatment with carbimazole. RESULTS: Serum fructosamine concentrations ranged from 154 to 267 mumol/L (median, 198 mumol/L) and were significantly lower than values in healthy cats. Eleven (50%) of the hyperthyroid cats had serum fructosamine concentrations less than the reference range. Serum fructosamine concentrations in hyperthyroid, normoproteinemic cats did not differ from values in hypoproteinemic cats. During treatment, an increase in serum fructosamine concentration was detected. CONCLUSIONS AND CLINICAL RELEVANCE: In hyperthyroid cats, concentration of serum fructosamine may be low because of accelerated protein turnover, independent of blood glucose concentration. Serum fructosamine concentrations should not be evaluated in cats with overt hyperthyroidism and diabetes mellitus. Additionally, concentration of serum fructosamine in hyperthyroid cats should not be used to differentiate between diabetes mellitus and transitory stress-related hyperglycemia.

Animals↗
PubMed1984

T3-hyperthyroidism caused by enhanced and shifted T4-conversion.

Radioactivities of endogenously labelled thyroid hormones following in vivo application of 131 I and extraction from serial blood samples, show that T4 secretion is enhanced in T3-hyperthyroidism as it is in T4-T3-hyperthyroidism. In an extreme case of T3-hyperthyroidism with serum concentrations (SC) of T3 nearly equal to T4 (1000 ng/dl and 1800 ng/dl, respectively) tracer studies revealed a very short half life of T4 when compared to T3 (21.8 and 20.2 hrs., respectively). In 110 cases with both types of hyperthyroidism, regression analysis showed that T3/T4 ratio as an indicator of T4 conversion, as well as T3/rT3 ratio as an indicator of the direction of the conversion, are related to T4SC (r = -0.84 and -0.72, respectively, p less than 0.001). T3-hyperthyroidism is described by high values of these ratios. For the definition of T3-hyperthyroidism it is suggested that both T4 and rT3SC are within the normal range (T4 less than or equal to 11.5 micrograms/dl, rT3 less than or equal to 43.0 ng/dl) and according to this definition, T3/rT3 is higher than in T4-T3-hyperthyroidism and in an undefined group (24.8 +/- 4.5 vs. 6.3 +/- 0.4 or 7.5 +/- 0.4, respectively). By means of the ratios the undefined group may be allocated to T4-T3-hyperthyroidism. The T3/rT3 ratio is value of greater than 10 has a frequency of 88% in thus defined T3-hyperthyroidism and a ratio of less than or equal to 10 is found in 90% of the other cases.(ABSTRACT TRUNCATED AT 250 WORDS)

Granulocytes↗
PubMed1995

Radioiodine therapy compared in patients with toxic nodular or Graves' hyperthyroidism.

In view of uncertainty regarding the most appropriate radioiodine dose for patients with hyperthyroidism due to toxic nodular disease or Graves' disease, we prospectively studied outcome in patients with these disorders given a single 5 mCi (185 MBq) dose of radioiodine. We studied 103 patients receiving their first radioiodine dose; 44 with toxic nodular hyperthyroidism and 59 with Graves' hyperthyroidism. Thyroid status (off anti-thyroid drug therapy) at 6 and 12 months after radioiodine was related to diagnosis, use of carbimazole before or after radioiodine, and physical and biochemical findings. At 6 months, persistent hyperthyroidism was less frequent in toxic nodular disease than in Graves' disease (34.1% vs. 55.9%, p < 0.05); hypothyroidism was also less frequent (11.4% vs. 27.1%, p < 0.05). Those with persistent hyperthyroidism at 6 months were given a second (10 mCi, 370 MBq) dose of radioiodine. At 12 months after the first dose, 80.6% of the group with toxic nodular hyperthyroidism were either euthyroid or hypothyroid, and 74.5% of those with Graves' disease were euthyroid or hypothyroid, the rate of hypothyroidism again being less in toxic nodular disease (19.4% vs. 58.8%, p < 0.05). Logistic regression and stepwise discriminant analysis demonstrated that 'cure' (euthyroidism or hypothyroidism) at 6 months was related to serum free T4 at presentation (p < 0.001) and administration of carbimazole before or after radioiodine (p < 0.001) (severe hyperthyroidism and carbimazole increasing the likelihood of persistent hyperthyroidism) but was not related to the diagnosis of toxic nodular or Graves' hyperthyroidism.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1993

[31P-magnetic resonance spectroscopy: impaired energy metabolism in latent hyperthyroidism].

31Phosphorus magnetic resonance spectroscopy allows an in vivo examination of energy metabolism. The present study was designed to evaluate whether in patients with latent hyperthyroidism alterations of muscle energy metabolism could be found similar to those observed in patients with overt hyperthyroidism. In 10 patients with overt hyperthyroidism before therapy and 20 with latent hyperthyroidism (also without therapy) and in 24 healthy volunteers magnetic resonance spectroscopy of the calf muscle was performed within a 1.5-Tesla magnet. Muscle concentrations of phosphocreatine, inorganic phosphate, and ATP were quantified compared to an external standard solution of K2HPO4. In the patients with overt hyperthyroidism and with latent hyperthyroidism a significant decrease of phosphocreatine was found. Further, the ATP concentration in patients with latent and manifest hyperthyroidism tended towards lower values. There were no significant differences in the decrease of phosphocreatine and ATP between both patient groups. Therefore, this study for the first time shows that alterations of energy metabolism in latent hyperthyroidism can be measured and that they are similar to those observed in overt hyperthyroidism.

Adult↗
PubMed1997

Pharmacokinetics of propranolol in healthy cats during euthyroid and hyperthyroid states.

OBJECTIVE: To examine the pharmacokinetic profile of propranolol in cats before and during experimentally induced hyperthyroidism. ANIMALS: 8 conditioned, random-source, young adult, female cats. PROCEDURE: Propranolol was administered i.v. as a single bolus and 72 hours later by mouth. Thereafter, the cats were dosed for 5 weeks with L-thyroxine (50 micrograms/kg of body weight, s.c., once daily) to induce hyperthyroidism (serum thyroxine concentration, 217 +/- 17 nmol/L). Blood samples were obtained at appropriate intervals before and during hyperthyroidism and were analyzed for plasma propranolol concentration by use of high-performance liquid chromatography. RESULTS: In all cats, a two-compartment model best described the control and hyperthyroid intravenous data. The change in thyroid status from euthyroid to hyperthyroid caused a significant (P < 0.05), but small reduction in propranolol area under the curve (19,932 +/- 7,900 min.micrograms/L vs 15,911 +/- 1,400 min.micrograms/L) after i.v. administration. In contrast, after oral administration during the hyperthyroid state, a twofold increase (P < 0.05) in propranolol area under the curve (105,430 +/- 57,600 min.micrograms/L vs 226,811 +/- 112,000 min.micrograms/L) and peak serum propranolol concentration (651 +/- 247 micrograms/L vs 1191 +/- 590 micrograms/L) were attributed to significant (P < 0.05) increase in propranolol bioavailability caused by increased fractional absorption (57 +/- 28% vs 137 +/- 73%) and decreased total body clearance (58 +/- 27 ml/min/kg vs 30 +/- 19 ml/min/kg). Mean arrival time after oral dosing was significantly lengthened by hyperthyroidism (100 +/- 38 minutes vs 157 +/- 71 minutes). CLINICAL RELEVANCE: Hyperthyroidism-induced changes in propranolol pharmacokinetics may signal the need to reduce doses of propranolol when they are orally administered to hyperthyroid cats.

Administration, Oral↗
PubMed1998

[Atrial fibrillation and hyperthyroidism. The results of a retrospective study].

BACKGROUND: To examine the prevalence of atrial fibrillation (AF) in cardiopathic patients with hyperthyroidism. METHODS: The data concerning the patients had been derived from registers of the Laboratory of Radioimmunoassay where cardiopathic patients' blood samples were referred from the Cardiology Unit to evaluate thyroid function, consecutively from January 1992 to December 1997. Of the 443 patients, 303 (68.4%) were classified as being euthyroid, 23 (5.2%) hypothyroid, 117 (26.4%) hyperthyroid. Thyroid function was diagnosed clinically and confirmed by serum TSH and free thyroid hormone (FT3, FT4), levels. RESULTS: Among hyperthyroid patients, the more frequent arrhythmia was AF (54.7%). After excluding from the study those hyperthyroid patients with rheumatic disease, hypertension, myocardial infarction, 37 hyperthyroid patients were selected; 18 (48.6%), (mean age 63.4 +/- 10.8 yrs), showed sinus rhythm and 19 (51.4%), (mean age 66.0 +/- 12.1 yrs), showed AF. FT3 and FT4 were higher in patients with AF than in those without AF, whereas TSH was not significantly different between the groups. Left ventricular (LV) mass index was significantly increased in hyperthyroid women with AF compared with hyperthyroid women without AF (109.80 +/- 22.33 g/m2 vs 84.50 +/- 6.20 g/m2; p < 0.005). A significant correlation was found between FT3 levels and LV mass index in the hyperthyroid women with and without AF (r = 0.77; p < 0.001). CONCLUSIONS: In this study the prevalence of AF is 51.4% in hyperthyroid patients. FT3 is higher in patients with AF than in those without AF. Finally, the correlation between FT3 and LV mass index suggests that cardiac hypertrophy is associated with thyroid hyperfunction.

Adolescent↗
PubMed1999

Comparison of radioiodine with radioiodine plus lithium in the treatment of Graves' hyperthyroidism.

Effectiveness of radioiodine for Graves' hyperthyroidism depends also on its intrathyroidal persistence. The latter is enhanced by lithium by blocking iodine release from the thyroid. One hundred ten patients with Graves' hyperthyroidism were randomly assigned to treatment with radioiodine or radioiodine plus lithium, stratified according to goiter size (< or =40 or >40 mL) and evaluated for changes in thyroid function and goiter size, at monthly intervals, for 12 months. Cure of hyperthyroidism occurred in 33 of 46 patients (72%) treated with radioiodine and in 45 of 54 patients (83%) treated with radioiodine plus lithium. The probability of curing hyperthyroidism was higher and its control prompter (P = 0.02) in the radioiodine-plus-lithium group. Patients with < or =40-mL goiters had similar persistence of hyperthyroidism (13%), but lithium-treated patients had hyperthyroidism controlled earlier (P = 0.04). Among patients with >40-mL goiters, hyperthyroidism was cured in 6 of 15 patients (40%) treated with radioiodine alone and in 12 of 16 patients (75%) treated with radioiodine plus lithium (P = 0.07), and cure occurred earlier in the latter (P = 0.05). Goiters shrank in both groups (P < 0.0001), more effectively and promptly (P < 0.0005) in the radioiodine-plus-lithium group. Serum free T4 and T3 levels increased shortly after therapy only in the radioiodine group (P < 0.01). Lithium carbonate enhances the effectiveness of radioiodine therapy, in terms of prompter control of hyperthyroidism, in patients with small or large goiters. In the latter group, lithium also increases the rate of permanent control of hyperthyroidism.

Combined Modality Therapy↗
PubMed1986

A unique pressor response to isoprenaline in the pithed rat during triiodo-L-thyronine(T3)-induced hyperthyroidism.

Thyroid hormone appears to be involved in the regulation of beta-adrenoceptors affecting cardiovascular performance. In the present study, the influence of hyperthyroidism on beta-adrenoceptor-mediated response of the cardiovascular system was investigated in vivo using the pithed rat preparation. Hyperthyroidism was induced by triiodothyronine injections (500 micrograms/kg, i.p.) for 6 days. A markedly accelerated basal heart rate and a wider pulse pressure with a significantly elevated systolic blood pressure were observed in hyperthyroid pithed rats. Although the basal and the maximal heart rates were increased in hyperthyroid rats, EC50 of the heart rate response to isoprenaline did not significantly differ between euthyroid and hyperthyroid pithed animals. Markedly different responses of blood pressure to isoprenaline were obtained in the two groups; isoprenaline caused a dose-dependent decrease in diastolic pressure in euthyroid pithed rats, whereas it produced pressor response in hyperthyroid pithed rats. This unique pressor response to isoprenaline observed in hyperthyroid pithed rats was abolished by the beta 1-adrenoceptor selective antagonist metoprolol but not by the alpha-adrenoceptor antagonist phenoxybenzamine. The density of myocardial binding sites of the beta-type was markedly increased after T3 treatment (65%), whereas that of the mesenteric artery was not altered. The results indicate that thyroid hormone exerts different effects on cardiac and vascular beta-adrenoceptors, and this different susceptibility to thyroid hormone may in part be responsible for the altered response of blood pressure to isoprenaline seen in hyperthyroid pithed rats.

Animals↗
PubMed1993

Function and energy metabolism of isolated hearts obtained from hyperthyroid spontaneously hypertensive rats (SHR). A 31P-nuclear magnetic resonance study.

It was the aim of this study to evaluate the effects of hyperthyroidism on heart function and cardiac energy metabolism of spontaneously hypertensive (SHR) rats. Hyperthyroidism was induced by daily injections of T3 (0.2 mg/kg s.c.) for 14 days. The hearts were then isolated and perfused in the Langendorff mode. ATP, phosphocreatine (PCr), and inorganic phosphate (Pi) were measured continuously by means of 31P-nuclear magnetic resonance (NMR) spectroscopy. Work load was altered by varying stepwise the Ca++ concentration in the perfusion fluid from 0.5 to 1.0, 1.5, and 2.0 mM, respectively. At every elevation of the Ca++ concentration, the increase in left ventricular developed pressure (LVDP) was higher in the hyperthyroid SHR than in the untreated SHR hearts. The ATP and PCr concentrations were lower in the hyperthyroid SHR compared to the untreated SHR hearts throughout the perfusion period. PCr decreased at every Ca++ elevation in both the untreated and hyperthyroid SHR hearts. The PCr/ATP ratio was not altered at any Ca++ concentration neither in the untreated SHR nor in the hyperthyroid SHR hearts. The Ca(++)-induced stepwise elevation in LVDP was higher at any given PCr/Pi ratio in the hyperthyroid SHR than in the untreated SHR hearts. Thus, the Ca(++)-inducible contractile reserve was greater in the hyperthyroid SHR heart.

Adenosine Triphosphate↗
PubMed1981

Hypercalcemia in hyperthyroidism. Role of age and goiter type.

Hyperthyroidism is often associated with hypercalcemia which is provoked by osteoclastic activity of the thyroid hormones. These data show that hypercalcemia develops with increasing age and in the presence of a special type of hyperthyroid goiter. Total serum calcium, total protein, and albumin as well as different parameters of thyroid function, namely T3 RIA1, T4 test, ETR and TRH test were determined in a group of 147 patients. The ionized calcium level was estimated from total calcium and albumin. 211 measurements were performed. Hyperthyroidism existed in 92 cases. Total calcium was not significantly elevated in hyperthyroidism. Hyperthyroid patients under 61 years of age showed elevated ionized calcium levels in only 2.3% and patients over 60 years of age in 18.8% of cases. Elevated ionized serum calcium levels were observed in 43.8% of hyperthyroid patients with multinodular goiters. The linear correlation between ionized calcium levels and different parameters of thyroid function is much more pronounced in the older group and it was found to be highly significant. 7 of 9 hyperthyroid patients with elevated ionized calcium levels showed multinodular goiters, though no autonomous adenoma. In the hyperthyroid group of patients of over 60 years of age with multinodular goiters the incidence of hypercalcemia was 43.8%. Direct action of thyroid hormone on calcium turnover as well as increasing age and special goiter type seem to be responsible for disturbances in calcium metabolism. A possible calcitonin deficiency in the above mentioned conditions is discussed.

Age Factors↗
PubMed1995

Hyperthyroidism increases adenosine transport and metabolism in the rat heart.

Hyperthyroidism induces a number of metabolic and physiological changes in the heart including hypertrophy, increase in inotropic status, and alterations of myocardial energy metabolism. The effects of hyperthyroidism on adenosine metabolism which is intimately involved in the control of many aspects of myocardial energetics, have not been clarified. The aim of this study was thus to evaluate the potential role of adenosine in the altered physiology of the hyperthyroid heart. Transport of adenosine was studied in cardiomyocytes isolated from hyperthyroid and euthyroid rats. Activities of different enzymes of purine metabolism were studied in heart homogenates and concentrations of nucleotide and creatine metabolites were determined in hearts freeze-clamped in situ. Both transport of adenosine into cardiomyocytes and the rate of intracellular phosphorylation were higher in the hyperthyroid rat. At 10 microM concentration, adenosine transport rates were 275 and 197 pmol/min/mg protein in hyperthyroid and euthyroid cardiomyocytes respectively whilst rates of adenosine phosphorylation were 250 and 180 pmol/min/mg prot. An even more pronounced difference was observed if values were expressed per number of cells due to cardiomyocyte enlargement. Hyperthyroidism was associated with a 20% increase in adenosine kinase, 30% decrease in membrane 5'-nucleotidase and 15% decrease in adenosine deaminase activities measured in heart homogenates. In addition there was a substantial depletion in the total creatine pool from 63.7 to 41.6 mumol/g dry wt, a small decrease in the adenylate pool (from 27.2 to 24.3 mumol/g dry wt) and an elevation of the guanylate pool (from 1.22 to 1.36). These results show that adenosine transport and phosphorylation capacity is enhanced in hyperthyroidism.(ABSTRACT TRUNCATED AT 250 WORDS)

AMP Deaminase↗
PubMedDate not supplied

Independent mechanisms for the chronotropic and inotropic responses in hyperthyroidism.

We established a hyperthyroid rat model and compared the hemodynamic responses of the hypertrophied rat heart in vivo and in vitro. Heart rate (557 +/- 26 beats/min), systolic blood pressure (162 +/- 5 mmHg) and dry heart mass (230 +/- 11 mg) in hyperthyroid rats were significantly greater than in control animals (408 +/- 12 beats/min, 140 +/- 5 mmHg and 193 +/- 4 mg respectively). In vitro studies were performed in order to eliminate neurohumoral and peripheral circulatory factors which are present in vivo. In the in vitro "working" heart preparation, there was no significant difference between the heart rates of L-thyroxine-treated (263 +/- 9 beats/min) and control (258 +/- 10 beats/min) animals, implying that the tachycardia of hyperthyroidism is partly mediated by in vivo factors. Consistent with this hypothesis was the observation that the hyperthyroid heart was more sensitive to the chronotropic effects of physiological concentrations of the synthetic catecholamine, isoproterenol (10(-8) M, 10(-7) M) than the control heart. The maximum rate of left ventricular pressure rise (dP/dtmax) was used as an index of myocardial contractility. In vitro values for dP/dtmax were significantly greater in hearts from hyperthyroid rats (5338 +/- 228 mmHg/s) than in control hearts (4583 +/- 158 mmHg/s), suggesting that the increased contractile response of hyperthyroidism is intrinsic to the heart itself. Although persistence of the inotropic response of the hyperthyroid heart in vitro was associated with an increase in heart mass, this factor alone did not account entirely for the enhanced contractility. It appears that intrinsic functional changes also contribute to the inotropic response of the hyperthyroid heart.

Animals↗
PubMed1999

[Incidence of immunogenic hyperthyroidism after radioiodine therapy of focal thyroid gland autonomy. Results of a multicenter study].

BACKGROUND: There are case reports in the literature that patients occasionally develop immunogenic hyperthyroidism 2 to 14 months following iodine-131-therapy of focal, non-immunogenic, autonomous thyroid nodules with a prevalence between 0.05 and 2.5%. Purpose of this multicenter evaluation was to assess the appearance of this phenomenon in a larger patient population. PATIENTS AND METHODS: So far 2867 patients out of 4 university hospitals are included in our study focusing on the appearance of pathologically elevated levels of thyrotropin-receptor-antibodies (TRAb) combined with hyperthyroidism following iodine-therapy. Records of the patients were screened for pre- and post-therapeutic biochemical tests, scintigraphic uptake patterns and ultrasound findings of the thyroid. RESULTS: Nineteen of 2867 patients with pretherapeutically scintigraphic "hot nodules" developed recurrent hyperthyroidism suggestive for immunogenic genesis 2 to 12 months following iodine-131-therapy (elevated TRAb-levels, homogeneous uptake in Tc-99m-pertechnetate scans). Pretherapeutically, 9 of these patients presented with a strictly focal scintigraphic uptake-pattern, 10 cases with a mixed disseminated-focal pattern. Because of missing pretherapeutic TRAb-tests in 8/9 patients presenting with a strictly focal scintigraphic uptake pattern, postradiogenic immunogenic hyperthyroidism could be reliably assessed in 1 case only. CONCLUSION: One could speculate that iodine-131-therapy may stimulate immunogenic mechanisms finally leading to immunogenic hyperthyroidism. Posttherapeutically observed hyperthyroidism following iodine-treatment might be based on an exacerbation of a preexisting--clinically not relevant/detectable--immunothyropathia. Also pretherapeutic TRAb-negative immunogenic hyperthyroidism could not be definitely excluded. Our multicenter data collected in a large patient population show similar results to the case reports of immunogenic hyperthyroidism following iodine-131-treatment in smaller populations. Therfore, the occurrence of this phenomenon plays a minor role regarding to its prevalence. Therapeutical consequences in treatment of functional thyroid autonomy are not recommended.

Adult↗
PubMed1988

The different types of hyperthyroidism in Europe. Results of a prospective survey of 924 patients.

In a prospective multicentric study, 924 untreated hyperthyroid patients were investigated, coming consecutively within one year into 17 thyroid centers of 6 European countries. With the aid of clinical information, evaluation of thyroid scan and centrally assayed thyroid hormones, thyroid antibodies, TSH-binding inhibiting immunoglobulins (TBII), and urinary iodine, different types of hyperthyroidism could be shown. Two types of hyperthyroidism could be defined directly: autonomous adenoma in cases of hot nodules in thyroid scan and Graves' disease, defined as hyperthyroidism with eye symptoms, and/or measurable TBII levels. The remainder, called "non-classifiable", included TBII negative Graves' patients, comprising of Hashitoxicosis, toxic nodular goiter, and other multifocal autonomies. 9.2% of the patients had an autonomous adenoma, 59.6% Graves' disease, and 31.2% unclassified hyperthyroidism. The main and significant difference between these types were mean age, goiter size, nodularity, and severity of the disease, being especially expressed in Graves' disease. Graves' patients had significantly increased T3/T4 ratios. Using as additional criteria diffuse regular uptake and/or increased T3/T4 ratios for immunogenic types of hyperthyroidism at least half of the 31.2% unclassified hyperthyroidism are probably Graves' disease. Forming two groups of iodine-deficient areas (IDA) and iodine-sufficient areas (ISA) according to the urinary iodine, it was possible to elucidate some characteristics independently of local factors. Autonomous adenoma was more frequent in IDA (10.1%) than in ISA (3.2%). Differences in iodine supply are reflected in the three types of hyperthyroidism by a significant higher prevalence of goiter, thyroid nodularity, lower thyroid hormone concentrations, and a higher rate of T3 toxicosis in IDA.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed2000

Constitutively activating TSH-receptor mutations as a molecular cause of non-autoimmune hyperthyroidism in childhood.

BACKGROUND: The glycoprotein hormone TSH (thyroid-stimulating hormone) and its receptor, the TSH-receptor (TSHR), play a crucial role in thyroid growth and function. Constitutively activating germline mutations within the TSHR gene were identified in patients with sporadic or familial non-autoimmune hyperthyroidism. Inheritance of these mutations is autosomal dominant. PATIENTS AND METHODS: We investigated two patients with neonatal onset of non-autoimmune hyperthyroidism and two families in whom the child and one parent are affected. RESULTS: Hyperthyroidism was difficult to treat in all of these patients and was complicated by premature craniosynostosis. Sequencing of all exons of the TSHR gene in one family with hyperthyroidism revealed a mutation in exon 10 (T6321), which was first identified in toxic adenomas and found to constitutively activate the TSHR. In the other family, we identified a new mutation in the first membrane spanning segment (G431S). In both patients with sporadic hyperthyroidism, a heterozygous mutation in exon 9 (S281N) was detected. The functional characterization of S281N and G431S demonstrated that both mutants were constitutively active. Therefore, these mutations are the molecular cause of non-autoimmune hyperthyroidism in the patients. CONCLUSIONS: For patients suffering from non-autoimmune hyperthyroidism, screening for mutations and their functional characterization is recommended. In case of an ineffective hyperthyroidism treatment, thyroidectomy should be performed to prevent lengthy anti-thyroid drug treatment and complications like premature craniosynostosis.

Child↗
PubMed1992

Hyperthyroidism due to inappropriate secretion of thyrotropin in 10 patients.

PURPOSE: The syndrome of inappropriate thyroid-stimulating hormone (TSH) secretion, characterized by elevated serum free thyroxine and triiodothyronine levels in association with measurable serum TSH concentrations, remains an uncommon cause of hyperthyroidism that is being recognized with increasing frequency. The hyperthyroidism may be due to either neoplastic pituitary TSH secretion or selective pituitary resistance to thyroid hormone. In an effort to better understand this rare cause of hyperthyroidism, we undertook a retrospective analysis of our institution's experience with this condition. PATIENTS: We reviewed our cumulative experience (10 patients) with hyperthyroidism due to the syndrome of inappropriate secretion of TSH. RESULTS: Six patients were diagnosed with TSH-secreting pituitary adenomas and four were found to have selective pituitary resistance to thyroid hormone. One patient with tumor had a TSH-secreting pituitary adenoma in the setting of multiple endocrine neoplasia syndrome. In all patients with tumor, hyperthyroidism was successfully treated with transsphenoidal adenomectomy with or without pituitary radiotherapy. All four patients with pituitary resistance had thyroid ablation or resection prior to their correct diagnosis. Therefore, therapy for this group of patients involved thyroid hormone replacement and efforts to suppress TSH hypersecretion. All 10 patients have done well clinically, with follow-up ranging from 2 weeks to 13 years. CONCLUSIONS: Adequate treatment exists for the two primary causes of TSH hypersecretion. TSH-secreting pituitary adenomas are treated with surgery and, if necessary, adjuvant pituitary radiotherapy. The results are generally good if the tumor is diagnosed and treated at an early stage. Primary therapy for hyperthyroidism due to selective pituitary resistance to thyroid hormone is aimed at suppression of pituitary TSH hypersecretion. The evaluation of any patient with hyperthyroidism must be thorough and, in some cases, should include measurement of TSH to determine the presence of inappropriate secretion. Eliminating this diagnosis will help avoid improper and potentially harmful treatment of hyperthyroid patients.

Adenoma↗