Central Hypothyroidism Patients Research Articles

Subclinical central hypothyroidism in patients with hypothalamic-pituitary disease: does it exist?

Central hypothyroidism (CH) is characterized by decreased thyroid hormone production due to insufficient stimulation of an otherwise normal thyroid gland by TSH. In patients with established hypothalamic-pituitary disease, a low FT4 concentration is considered highly specific, although poorly sensitive, for the diagnosis of CH. That would be comparable to diagnosing primary hypothyroidism in patients at risk only when serum FT4 concentrations are below the reference range, missing all patients with subclinical primary hypothyroidism and preventing proper therapy in patients in which thyroxine replacement is clearly beneficial. Cardiac time intervals, especially the isovolumic contraction time (ICT), have been considered the gold standard of peripheral thyroid hormone action. Using Doppler echocardiography, we have previously shown a very high proportion of prolonged ICT in patients with hypothalamic-pituitary disease and serum FT4 levels indistinguishable from controls. As ICT decreased/normalized after thyroxine-induced increases in FT4 concentrations within the normal reference range, prolonged ICT was considered a bona fide diagnostic biomarker of subclinical CH. Those findings challenge the usual interpretation that FT4 concentrations in the mid-reference range exclude hypothyroidism in patients with hypothalamic-pituitary disease. Rather, subclinical central hypothyroidism, a state analogous to subclinical primary hypothyroidism, seems to be frequent in patients with hypothalamic-pituitary disease and normal FT4 levels. They also challenge the notion that thyroid function is usually the least or the last affected in acquired hypopituitarism. The relevance of Doppler echocardiography to correctly diagnose and monitor replacement therapy in both clinical and subclinical forms of CH should improve quality of life and decrease cardiovascular risk, as already demonstrated in patients with clinical and subclinical primary hypothyroidism.

The TRH test provides valuable information in the diagnosis of central hypothyroidism in patients with known pituitary disease and low T4 levels.

To evaluate the value of the thyrotropin-releasing hormone (TRH) test in the diagnosis of central hypothyroidism (CH) in patients with pituitary disease. Systematic evaluation of 359 TRH tests in patients with pituitary disease including measurements of thyroxine (T4), TBG-corrected T4 (T4corr), baseline TSH (TSH0) and relative or absolute TSH increase (TSHfold, TSHabsolute). Patients diagnosed with CH (n=39) show comparable TSH0 (p-value 0.824) but lower T4corr (p-value <0.001) and lower TSH increase (p-value <0.001) compared to patients without CH. In 54% (42 of 78 cases) of patients with low T4corr, the CH diagnosis was rejected based on a high TSHfold. In these cases, a spontaneous increase and mean normalization in T4corr (from 62 to 73 nmol/L, p-value <0.001) was observed during the follow-up period (7.6 ± 5.0 years). Three of the 42 patients (7%) were started on replacement therapy due to spontaneous deterioration of thyroid function after 2.8 years. Patients diagnosed with CH reported significantly more symptoms of hypothyroidism (p-value 0.005), although, symptoms were reported in most patients with pituitary disease. The TRH test did not provide clinical relevant information in patients with normal T4 or patients awaiting pituitary surgery (78%, 281 of 359). There were only mild and reversible adverse effects related to the TRH test except for possibly one case (0.3%) experiencing a pituitary apoplexy. The TRH test could be reserved to patients with pituitary disease, low T4 levels without convincing signs of CH. Approximately 50% of patients with a slightly decreased T4 were considered to have normal pituitary thyroid function based on the TRH test results.

Early diagnostic tools in milder forms of central hypothyroidism in patients harbouring a pituitary adenoma: cross-sectional study on 142 patients from a single tertiary center

Early diagnostic tools in milder forms of central hypothyroidism in patients harbouring a pituitary adenoma: cross-sectional study on 142 patients from a single tertiary center

Central hypothyroidism or subclinical hyperthyroidism: can they be confused with each other?

SummaryIsolated, adult-onset central hypothyroidism is very rare, and its diagnosis can be challenging. A 42-year-old patient was referred for evaluation of a 2.8 cm thyroid nodule. She referred symptoms that could be attributed to hypothyroidism and thyroid tests showed low TSH and normal-low levels of free T4. However, evaluation of the remaining pituitary hormones and pituitary MRI were normal, yet a radionuclide scanning revealed that the thyroid nodule was ‘hot’ and the tracer uptake in the remaining thyroid tissue was suppressed. Interpretation of these studies led to a misdiagnosis of subclinical hyperthyroidism and the patient was treated with radioiodine. Soon after treatment, she developed a frank hypothyroidism without appropriate elevation of TSH and the diagnosis of central hypothyroidism was made a posteriori. Long term follow-up revealed a progressive pituitary failure, with subsequent deficiency of ACTH and GH. This case should alert to the possibility of overlooking central hypothyroidism in patients simultaneously bearing primary thyroid diseases able to cause subclinical hyperthyroidism.Learning points:Although rarely, acquired central hypothyroidism can occur in the absence of other pituitary hormone deficiencies.In these cases, diagnosis is challenging, as symptoms are unspecific and usually mild, and laboratory findings are variable, including low, normal or even slightly elevated TSH levels, along with low or low-normal concentrations of free T4.In cases with low TSH levels, the coexistence of otherwise common disorders able to cause primary thyroid hyperfunction, such as autonomous nodular disease, may lead to a misdiagnosis of subclinical hyperthyroidism.

Evaluation of Treatment of Central Hypothyroidism Versus Primary Hypothyroidism in Relation to Levothyroxine Replacement Dose

Objective: The aim of this study was to evaluate levothyroxine (LT4) replacement daily doses in patients with central hypothyroidism (CeH) and compare them with those adequate for patients with primary hypothyroidism (P-HYPO). Methods: We included 53 patients with CeH and 57 with P-HYPO, matched by sex, age, weight, and body mass index, in the period of 1 year. At the time of inclusion, all presented a stable and adequate dose of LT4 for at least 3 months, considering as adequate the dose associated with normal thyroid-stimulating hormone (TSH) levels and free thyroxine (T4) in P-HYPO patients, and free T4 levels in CeH patients. Results: The absolute daily dose of LT4 differed significantly between the two groups, 103.0 ± 27.1 μg (CeH) and 89.3 ± 32.0 μg (P-HYPO) (P = .017), even after adjustment for age, gender, and free T4 (P = .04). The LT4 dose adjusted to weight was also higher after adjustment for age, gender and free T4 (P = .04), with an average of 1.3 ± 0.4 μg/kg (CeH) and 1.2 ± 0.4 μg/kg (P-HYPO). Sheehan syndrome patients had a lower absolute daily dose of LT4 (P = .001), and patients who underwent pituitary radiotherapy required higher doses (P = .008). There was no difference in the daily dose of LT4 according to other pituitary hormone deficiencies. Conclusion: The results reinforce the relevance of a careful individualization of LT4 replacement in CeH management and the need for new markers for proper LT4 replacement therapy in such cases. Abbreviations: BMI = body mass index; CeH = central hypothyroidism; GH = growth hormone; LT4 = levothyroxine; P-HYPO = primary hypothyroidism; T3 = triiodothyronine; T4 = thyroxine; TSH = thyroid-stimulating hormone.

Central Hypothyroidism Related to Pituitary Adenomas: Low Incidence of Central Hypothyroidism in Patients With Acromegaly.

The most frequent cause of central hypothyroidism (CeH) is pituitary adenomas, but the mechanisms remain unclear. We investigated serum thyroid levels and GH/IGF-1 in central hypothyroidism in untreated patients with pituitary nonfunctioning and GH-secreting adenomas. This was a retrospective cross-sectional study of cases collected from Gunma University and Toranomon Hospitals between 2007 and 2016. One-hundred thirty-nine cases of nonfunctioning pituitary adenoma (NFPA) and 150 cases of GH-secreting pituitary adenoma (GHPA) were analyzed. The correlations between thyroid levels, several clinicopathological parameters, and GH/IGF-1 were examined. Twenty-four percent of NFPA patients had CeH. The severity did not correlate with tumor size, age, or sex, and all cases had normal TSH levels. In contrast, only 8.7% of GHPA patients had CeH; approximately half had normal TSH levels and approximately half had low TSH levels. Serum TSH levels in GHPA patients were significantly lower and free T4 (FT4) and free T3 levels were higher than those in patients with NFPA. Furthermore, approximately one-fourth of GHPA patients had normal FT4 and low TSH levels. In addition, serum FT4 levels and serum TSH levels were positively and negatively correlated, respectively, with serum IGF-1 levels. Furthermore, IGF-1 levels in patients with GHPA decreased with age. (i) NFPA patients with CeH had TSH levels within a normal range. (ii) GHPA patients had a low incidence of CeH, which may be a result of stimulated thyroid function by GH/IGF-1. (iii) We found an age-dependent decrease in serum IGF-1 levels in patients with GHPA.

Central Hypothyroidism Related to Pituitary Adenomas: Resistance to Central Hypothyroidism in Patients with GH Secreting Pituitary Adenomas

Background: most frequent cause of central hypothyroidism (CeH) is pituitary adenomas, but the mechanisms remain unclear. We investigated thyroid status and GH/IGF-1 in CeH in untreated patients with pituitary non-functioning and GH-secreting adenomas. Methods: This was a retrospective cross-sectional study of cases collected from two Hospitals between 2007 and 2016. One hundred-thirty-nine cases of non-functioning (NFPA) and 150 cases of GH-secreting pituitary adenoma (GHPA) were analyzed. correlations between the thyroid status, several clinicopathological parameters, and GH/IGF-1 were examined. Findings: Twenty-four percent of NFPA patients had CeH. severity did not correlate with tumor size and age, and all cases had normal TSH levels. In contrast, only 8.7% of GHPA patients had CeH; about half had normal TSH levels and about half had low TSH levels. Serum TSH levels in GHPA patients were significantly lower and free T4 (FT4) and free T3 levels were higher than those in NFPA patients. One-fourth of GHPA patients had normal FT4 levels and low TSH levels. In addition, serum FT4 levels and serum TSH levels were positively and negatively correlated, respectively, with serum IGF-1 levels. Furthermore, IGF-1 levels in patients with GHPA decreased with age. Interpretation: 1) NFPA patients with CeH had TSH levels within a normal range. 2) GHPA patients were resistant to CeH, which may be a result of stimulated thyroid function by GH/IGF-1. 3) We found an age-dependent decrease in serum IGF-1 levels in a large cohort of GHPAs. Funding Statement: This work was supported by JSPS KAKENHI Grants 16K15493, 23591345, and 20591087 (to M.Y.) and 16K19551 (to K.H.). This work was partially supported by the Advancing Care of Hypothalamic-Pituitary Dysfunction in Japan Study (to M.Y.) from the Japan Agency for Medical Research and Development, and the Research on Rare and Intractable Disease, Health and Labour Sciences Research Grants (to M.Y.). Declaration of Interests: authors state: The authors have nothing to disclose. Ethics Approval Statement: studies were conducted in accordance with the principles of the Declaration of Helsinki and were approved by the Ethics Committee on human research of Gunma University (Approval number 535: Gunma University Human Genome Ethics Committee).

Transducin β-like 1, X-linked and nuclear receptor co-repressor cooperatively augment the ligand-independent stimulation of TRH and TSHβ gene promoters by thyroid hormone receptors.

Mutations in TBL1X, a component of the nuclear receptor co-repressor (N-CoR) and silencing mediator of retinoic acid and thyroid hormone receptor co-repressor complexes, have recently been implicated in isolated central hypothyroidism (CeH). However, the mechanisms by which TBL1X mutations affect negative feedback regulation in the hypothalamus-pituitary-thyroid axis remain unclear. N-CoR was previously reported to paradoxically enhance the ligand-independent stimulation of TRH and TSHβ gene promoters by thyroid hormone receptors (TR) in cell culture systems. We herein investigated whether TBL1X affects the unliganded TR-mediated stimulation of the promoter activities of genes negatively regulated by T3 in cooperation with N-CoR. In a hypothalamic neuronal cell line, the unliganded TR-mediated stimulation of the TRH gene promoter was significantly enhanced by co-transfected TBL1X, and the co-transfection of TBL1X with N-CoR further enhanced promoter activity. In contrast, the knockdown of endogenous Tbl1x using short interfering RNA significantly attenuated the N-CoR-mediated enhancement of promoter activity in the presence of unliganded TR. The co-transfection of N365Y or Y458C, TBL1X mutants identified in CeH patients, showed impaired co-activation with N-CoR for the ligand-independent stimulation of the TRH promoter by TR. In the absence of T3, similar or impaired enhancement of the TSHβ gene promoter by the wild type or TBL1X mutants, respectively, was observed in the presence of co-transfected TR and N-CoR in CV-1 cells. These results suggest that TBL1X is needed for the full activation of TRH and TSHβ gene promoters by unliganded TR. Mutations in TBL1X may cause CeH due to the impaired up-regulation of TRH and/or TSHβ gene transcription despite low T3 levels.

L-Thyroxine in an Oral Liquid or Softgel Formulation Ensures More Normal Serum Levels of Free T4 in Patients with Central Hypothyroidism.

l-Thyroxine (l-T4) therapy of central hypothyroidism (CH) is guided by measurements of serum free thyroxine (FT4), which should be above the midnormal range value (MNRV). In some countries, novel formulations of oral l-T4 (liquid or softgel) are available further to the classic tablets. The intestinal absorption of either novel formulation is greater than tablets in patients with primary hypothyroidism. To evaluate whether new oral formulations of l-T4 could be considered optimal in patients with CH who do not reach the FT4 target using tablet l-T4. Our observation of six patients with isolated CH and serum FT4 below MNRV under stable adequate doses of tablet l-T4 (median 1.51 μg/kg bw/day), prompted us to switch them to liquid (n = 4) or softgel (n = 3) l-T4 at the same dose, and verify whether FT4 increased above MNRV. A seventh patient with FT4 above MNRV was enrolled because she wanted a "more modern formulation." Postswitch FT4 was measured at least twice with the same kit as preswitch FT4. In the first six patients, postswitch FT4 averaged 13.0 ± 1.6 pg/ml compared to 10.4 ± 1.8 preswitch FT4 (P = 0.00026), with 11/13 (85%) measurements above MNRV compared to 0/20. In the liquid or softgel l-T4 group, postswitch FT4 averaged 13.1 ± 1.6 vs. 10.6 ± 0.9 pg/ml preswitch (P = 0.0004) or 12.9 ± 2.1 vs. 10.3 ± 2.4 (P = 0.048), respectively. In the seventh patient (switched to liquid l-T4), averages were 18.3 vs. 15.2 pg/ml, and proportions 4/4 vs. 2/2. In CH patients, oral liquid or softgel l-T4 administered at the same doses as tablet l-T4 ensures target serum FT4 levels above MNRV that tablet l-T4 may miss. In turn, this performance suggests the more favorable pharmacokinetics profile of either novel formulation compared with the tablet formulation.

Abstract #1043: Management f Central Hypothyroidism in Patients on an Antineoplastic Agent; Bexarotene

Abstract #1043: Management f Central Hypothyroidism in Patients on an Antineoplastic Agent; Bexarotene

Free T3 to free T4 ratio less than 2.0 suggests low T3 syndrome rather than central hypothyroidism from the age of two to eighteen years.

No serological cut-off exists to separate low T3 syndrome (LT) and central hypothyroidism (CH). The objective of this retrospective study was to propose such a cut-off. The first participant group comprised 52 patients from the age of six to twenty years. This group consisted of patients of 36 anorexia nervosa with LT and 16 CH. The second participant groups comprised 229 patients of all the same range of ages at the same hospital and included LT (n = 58) and CH (n = 4) patients, respectively. The third group of participants comprised 125 LT and 27 CH patients at the same hospital at all ages less than eighteen years. The last group of participants comprised 10 CH patients from the other two hospitals. The main outcome measure was fT3/fT4 ratio (pg/mL, ng/dL respectively). This ratio in the first group was significantly different (p < 0.05) between LT and CH. When the cut off value of fT3/fT4 was set as 2.0, the sensitivity of the LT and CH patients in the second group was 62% and 100%, respectively. This cut-off value of 2.0 was useful for distinguishing LT from CH only above the age of two years, as shown in the third group. The fT3/fT4 in 10 subjects with CH in the last group, aged 2 to 7 years, ranged from 2.55 to 7.71. In conclusion, fT3/fT4 less than 2.0 suggests LT rather than CH for patients from the age of two to eighteen years.

Mitotane treatment in patients with adrenocortical cancer causes central hypothyroidism.

Mitotane, a steroidogenesis inhibitor with adrenolytic properties used to treat adrenocortical cancer (ACC), can affect thyroid function. A reduction of FT4 levels with normal FT3 and TSH has been described in these patients. Using an in vitro murine model, the secretory capacity of thyrotrophic cells has been shown to be inhibited by mitotane. To investigate the pathogenesis of thyroid abnormalities in mitotane-treated patients with ACC. In five female patients with ACC (median age 47; range 31-65) treated with mitotane (dosage 1·5 g/day; 1·0-3·0), we analysed the pattern of TSH and thyroid function index (FT4, FT3 and FT3/FT4 ratio) compared to an age- and gender-matched control group. The in vivo secretory activity of the thyrotrophic cells was evaluated using a standard TRH test (200 μg), and the response was compared to both a group of age-matched female controls (n = 10) and central hypothyroid patients (n = 10). Basal TSH (median 1·54 mU/l; range 1·20-2·17) was normal and scattered around our median reference value, FT3 levels (median 3·80 pmol/l; 3·30-4·29) were normal but below the median reference value of 4·37 pmol/l and FT4 levels were below the normal range in all patients (median 8·40 pmol/l; 7·6-9·9). FT3/FT4 ratio was in the upper range in 4 patients and higher than normal in one patient. A blunted TSH response to TRH was observed in mitotane-treated patients. ΔTSH (absolute TSH response, peak TSH minus basal TSH) was 3·65 (range 3·53-5·26), 12·37 (range 7·55-19·97) and 1·32 mU/l (range 0·52-4·66) in mitotane-treated patients, controls and central hypothyroid patients, respectively. PRL secretion was normal. Mitotane-treated patients with ACC showed low FT4, normal FT3 and TSH and impaired TSH response to TRH, characteristic of central hypothyroidism. Furthermore, the elevated FT3/FT4 ratio of these subjects reflects an enhanced T4 to T3 conversion rate, a compensatory mechanism characteristic of thyroid function changes observed in hypothyroid conditions. This finding thus confirms in vitro studies and may have a therapeutic implication for treatment with thyroid hormones, as suggested by current guidelines for this specific condition.

Diagnosis of subclinical central hypothyroidism in patients with hypothalamic–pituitary disease by Doppler echocardiography

The diagnosis of subclinical central hypothyroidism in hypothalamic-pituitary patients cannot be established by serum markers of thyroid hormone action. Myocardial function by echocardiography has been shown to reflect thyroid hormone action in primary thyroid dysfunction. We evaluated the performance of echocardiography in diagnosing subclinical central hypothyroidism. Cross-sectional and before and after. Echocardiography and serum thyroid hormones were assessed in overt primary (n=20) and central (n=10) hypothyroidism, subclinical primary hypothyroidism (n=10), hypothalamic-pituitary disease with normal free thyroxine (FT(4); n=25), and controls (n=28). Receiver operating characteristic (ROC) curves were generated using overt hypothyroidism patients and selected cut-off values were applied to detect both primary and central subclinical hypothyroidism. After levothyroxine (l-T(4)) intervention, patients were echocardiographically reevaluated at predefined targets: normal thyrotropin (TSH) in primary hypothyroidism, normal FT(4) in overt central hypothyroidism, and higher than pretreatment FT(4) in echo-defined subclinical central hypothyroidism. Parameters with highest areas under the ROC curves (area under the curve (AUC) ≥0.94) were as follows: isovolumic contraction time (ICT), ICT/ejection time (ET), and myocardial performance index. Highest diagnostic accuracy (93%) was obtained when at least one parameter was increased (positive and negative predictive values: 93%). Hypothyroidism was echocardiographically diagnosed in eight of ten patients with subclinical primary hypothyroidism and in 14 of 25 patients (56%) with hypothalamic-pituitary disease and normal serum FT(4). Echocardiographic abnormalities improved significantly after l-T(4) and correlated (0.05<P<0.001) with changes in FT(4) (-0.62<r<-0.55) and TSH (0.63<r<0.68) in primary hypothyroidism and with FT(4) in central hypothyroidism (-0.72<r<-0.50). Echocardiography can be useful in diagnosing subclinical central hypothyroidism in patients with hypothalamic-pituitary disease.

The metabolic consequences of thyroxine replacement in adult hypopituitary patients

The metabolic consequences of thyroxine replacement in patients with central hypothyroidism (CH) need to be evaluated. The aim was to examine the outcome of thyroxine replacement in CH. Adult hypopituitary patients (n = 1595) with and without CH from KIMS (Pfizer International Metabolic Database) were studied before and after 2 years of GH replacement. CH patients (CH, n = 1080) were compared with TSH sufficient patients (TSHsuff n = 515) as one group and divided by thyroxine dose/kg/day into tertiles (CHlow-mid-high). Anthropometry, fasting glucose, glycosylated haemoglobin (HbA1c), blood pressure, lipids, IGF-I SDS, quality of life and morbidity were studied. Analyses were standardized for gender, age, number and types of pituitary insufficiencies, stimulated GH peak, age at GH deficiency onset, aetiologies and, when appropriate, for weight and GH dose. At baseline, TSHsuff patients did not differ from CH or CHmid in any outcome. CHlow (≤ 1.18 μg thyroxine/kg/day) had increased weight, BMI and larger waist circumference (WC), CHhigh (≥ 1.58 μg thyroxine/kg/day) had lower weight, BMI, WC and IGF-I than TSHsuff and compared to their predicted weights, BMIs and WCs. For every 0.1 μg/kg/day increase of thyroxine dose, body weight decreased 1.0 kg, BMI 0.3 kg/m(2), and WC 0.65 cm. The GH sensitivity of the CH group was higher (0.76 ± 0.56 SDS/mg GH) than that of TSHsuff patients (0.58 ± 0.64 SDS/mg GH), P < 0.001. The middle thyroxine dose (1.19-1.57 μg/kg/day) seems to be the most physiological. This is equivalent to 70, 100, 125 μg thyroxine/day for hypopituitary patients of 50, 70 or 90 kg weight, respectively.

Central hypothyroidism in patients with chronic hepatitis C and relation with interferon-alpha treatment

Since some authors referred to panhypopituitarism or central hypothyroidism during the treatment of chronic hepatitis C virus (HCV) infection using interferon-α, it is intended to evaluate the prevalence of central hypothyroidism (CH) in HCV patients before and during interferon-α therapy. We evaluated 308 HCV patients treated with standard interferon-α (IFN) and/or pegylated-interferon-α (PEG-IFN) associated with ribavirin. Free thyroxine (FT4) and thyrotropin (TSH) levels were measured before, during and after treatment. CH was diagnosed when the level of FT4 was lower than normal values with concomitant normal or lower TSH as verified at least in two consecutive measures. Before treatment, 18 (5.8 %) patients presented CH Twelve patients maintained laboratory changes during the treatment and 17 new patients developed central hypothyroidism. Among the 29 patients (9.4 %) with CH, 11 used IFN, six used PEG-IFN and 12 patients used two or more therapeutic schedules. The differences in gender, age, cirrhosis, viral genotype, duration of treatment and the type of interferon used were not statistically significant. The absence of sustained virologic response was associated with central hypothyroidism (OR=3.83). HCV patients may develop CH due to viral infection or during the interferon treatment. These patients presented 3.83 times more chance of not obtaining sustained virologic response.

TSH Regulation Dynamics in Central and Extreme Primary Hypothyroidism

Thyrotropin (TSH) changes in extreme primary hypothyroidism include increased secretion, slowed degradation, and diminished or absent TSH circadian rhythms. Diminished rhythms are also observed in central hypothyroid patients and have been speculated to be a cause of central hypothyroidism. We examined whether TSH secretion saturation, previously suggested in extreme primary hypothyroidism, might explain diminished circadian rhythms in both disorders. We augmented and extended the range of our published feedback control system model to reflect nonlinear changes in extreme primary hypothyroidism, including putative TSH secretion saturation, and quantified and validated it using multiple clinical datasets ranging from euthyroid to extreme hypothyroid (postthyroidectomy). We simulated central hypothyroidism by reducing overall TSH secretion and also simulated normal TSH secretion without circadian oscillation, maintaining plasma TSH at constant normal levels. We also utilized the validated model to explore thyroid hormone withdrawal protocols used to prepare remnant ablation in thyroid cancer patients postthyroidectomy. Both central and extreme primary hypothyroidism simulations yielded low thyroid hormone levels and reduced circadian rhythms, with simulated daytime TSH levels low-to-normal for central hypothyroidism and increased in primary hypothyroidism. Simulated plasma TSH showed a rapid rise immediately following triiodothyronine (T(3)) withdrawal postthyroidectomy, compared with a slower rise after thyroxine withdrawal or postthyroidectomy without replacement. Diminished circadian rhythms in central and extreme primary hypothyroidism can both be explained by pituitary TSH secretion reaching maximum capacity. In simulated remnant ablation protocols using the extended model, TSH shows a more rapid rise after T(3) withdrawal than after thyroxine withdrawal postthyroidectomy, supporting the use of replacement with T(3) prior to (131)I treatment.

Therapeutic Concentrations of Mitotane (o,p′-DDD) Inhibit Thyrotroph Cell Viability and TSH Expression and Secretion in a Mouse Cell Line Model

Mitotane therapy is associated with many side effects, including thyroid function perturbations mimicking central hypothyroidism, possibly due to laboratory test interference or pituitary direct effects of mitotane. We investigated whether increasing concentrations of mitotane in the therapeutic range might interfere with thyroid hormone assays and evaluated the effects of mitotane on a mouse TSH-producing pituitary cell line. TSH, free T(4), and free T(3) levels do not significantly change in sera from hypo-, hyper-, or euthyroid patients after addition of mitotane at concentrations in the therapeutic window. In the mouse TalphaT1 cell line, mitotane inhibits both TSH expression and secretion, blocks TSH response to TRH, and reduces cell viability, inducing apoptosis at concentrations in the therapeutic window. TRH is not capable of rescuing TalphaT1 cells from the inhibitory effects of mitotane on TSH expression and secretion, which appear after short time treatment and persist over time. Our results demonstrate that mitotane does not interfere with thyroid hormone laboratory tests but directly reduces both secretory activity and cell viability on pituitary TSH-secreting mouse cells. These data represent a possible explanation of the biochemical picture consistent with central hypothyroidism in patients undergoing mitotane therapy and open new perspectives on the direct pituitary effects of this drug.

Blunted nocturnal TSH surge does not indicate central hypothyroidism in patients after pituitary surgery.

The thyrotropin-releasing hormone stimulation test (TRH test) is commonly used as part of the endocrine evaluation after pituitary surgery. However, some patients with a normal thyrotropin (TSH) response to TRH after pituitary surgery develop central hypothyroidism during follow-up. On the other hand, hypothyroidism does not necessarily ensue in patients with a blunted TSH response. As TSH is secreted in a pulsatile fashion with maximum secretion in the early morning, we investigated whether measurement of the nocturnal TSH surge is useful for predicting development of thyrotropic function after pituitary surgery. Serum TSH concentrations were measured at hourly intervals from 16.00 h to 06.00 h in 13 healthy volunteers and in 10 patients within 2 weeks after pituitary surgery. A standard TRH test using i.v. injection of 200 microg synthetic TRH was performed the next morning. Three and six months later thyroid function was reassessed in all patients by measuring thyroid hormones and TSH. Healthy volunteers showed a clear nocturnal TSH surge from a nadir of 0.55 +/- 0.27 microIU/ml at 18.00 h to a peak concentration of 1.82 +/- 0.97 microU/ml at 06.00 h (p = 0.0015). DeltaTSH during TRH test was 6.31 +/- 2.27 microIU/ml. In contrast, following pituitary surgery, patients invariably showed a blunted nocturnal increase in TSH concentration, which was 0.27 +/- 0.20 microIU/ml at 18.00 h and 0.33 +/- 0.26 microIU/ml at 06.00 h (p = 0.044). DeltaTSH during TRH test was 1.99 +/- 2.51 microIU/ml and was subnormal in 8 out of 10 patients. Levothyroxine supplementation was initiated in two of these patients, because free T4 levels were also subnormal and clinical hypothyroidism was present. In the remaining patients with subnormal TRH response, no case of central hypothyroidism was identified at the follow-up visits after 3 and 6 months. We conclude from these data that both nocturnal TSH surge and TRH test are subnormal after pituitary surgery and do not indicate that central hypothyroidism will develop.

Do We Still Need the TRH Stimulation Test?

To evaluate the diagnostic value of the thyrotropin-releasing hormone (TRH) stimulation test in the diagnosis of central hypothyroidism in patients with Sheehan's syndrome. TRH stimulation test was performed in 72 patients with Sheehan's syndrome. Basal free triiodothyronine (fT(3)) and free thyroxine (fT(4)) levels were measured. Serum thyrotropin (TSH) concentration was determined before and 30, 60, 90, and 120 minutes after 200 mug TRH IV bolus injection. The peak TSH values <5.5 microIU/ml were defined as inadequate response. A peak TSH at 60 minutes or later was considered as delayed response. If TSH (60 minutes after peak), was more than 40% of the peak value it was considered as prolonged response. The diagnosis of central hypothyroidism (CH) was made if either serum fT(4) concentration was subnormal with an inappropriately low serum TSH concentration or inadequate response to TRH stimulation test and/or a delayed or prolonged response to TRH stimulation test. Fifty-six (77.7%) of the patients had low serum fT(4) and fT(3) levels with an inappropriately low serum TSH levels were defined as CH (CH0 group). Ten (13.8%) patients with normal and low-normal fT(4) levels had no response and/or delayed or prolonged response to TRH stimulation test (CH1group). Six (8.3%) patients had fT(3), fT(4), and TSH levels within normal limits and peak TSH responses >/=5.5 microIU/ml consistent with euthyroidism (euthyroid group). Thus, 66 (91.6%) of 72 patients with Sheehan's syndrome had CH. Although fT(4) levels were within normal reference range, TRH stimulation test revealed that 10 (13.8%) of these had CH. TRH stimulation test is useful in the diagnosis of central hypothyroidism, especially in whom fT(4) and/or TSH is low-normal and known to have hypothalamo-pituitary pathology.

Clinical and hormonal characteristics of central hypothyroidism at diagnosis and during follow-up in adult patients.

We studied the clinical and hormonal profiles of patients with central hypothyroidism (CH), the adequacy of levothyroxine (L-T4) treatment and the influence of other pituitary hormone replacement therapies. We reviewed medical records of 108 adult patients with child-onset (CO; n=26) or adult-onset (AO; n=82) CH. At diagnosis, the most frequently reported symptoms were fatigue and headaches in AO patients, and growth retardation in CO patients. Serum TSH was normal in a majority of CH patients, low in 8% and elevated in 8%. Serum free thyroxine (fT(4)) was usually reduced, but remained within the low normal range in 28% of the study population (mostly CO patients). Similarly, serum total T(4) (tT(4)), total triiodothyronine (tT(3)) and free T(3) (fT(3)) were found to be within the normal range in significant subsets of patients. Interestingly, the clinical and biochemical characteristics of CH patients with normal f/t T(4) levels were not different from those of the patients with low fT(4) values. The thyroid hormonal profile was not influenced by gender, etiology or by the number of hormone deficiencies. At last evaluation, the mean dose of L-T(4) was 1.6+/-0.5 microg/kg/day and was negatively correlated to current age (P<0.001) but positively correlated to the number of hormone deficiencies (P<0.05). Treatment suppressed TSH in 75% of the patients, induced normal fT(4) in 94%, but normal fT(3) in only 49% of them. Male GH-treated patients and estrogen-treated females needed a higher L-T(4) dose compared with non-treated patients. fT(4) is clearly the best indicator of CH, but remains in the low normal range in a significant subset of patients, especially in those with CO disease. Adequacy of therapy is mostly reflected by the combination of upper normal fT(4) and low normal fT(3) levels. Pituitary hormone replacement therapy may require an adjustment of T(4) treatment, as female patients under estrogen treatment and male patients under GH treatment will need a higher T(4) dose in order to remain in the euthyroid range.