Serum creatine kinase levels in overt and subclinical hypothyroidism

Effects of statin use on serum creatinine phosphokinase levels in normal thyroid function

BACKGROUND/AIMS

Statins are common lipid-lowering agents used in dyslipidemia. However, they increase serum creatinine phosphokinase (CPK) levels. Currently, there are no studies on the effect of thyroid-stimulating hormone (TSH) levels on CPK levels after statin administration. Therefore, this study aimed to investigate CPK level alterations after statin administration according to TSH quartiles in participants with euthyroidism.

METHODS

This retrospective analysis included 25,047 patients with euthyroidism. CPK levels were measured before and 6 months after statin administration. Normal TSH levels were divided into four quartiles, and the CPK levels and proportions of patients with normal CPK levels after statin administration for each TSH quartile were evaluated.

RESULTS

The baseline CPK level was significantly higher in the lowest TSH quartile (Q1) compared to the other quartiles but decreased after statin administration. Thus, the difference between the CPK levels and the other quartile groups was not significant. The proportion of patients with normal CPK levels was also significantly lowest in Q1 before statin administration; however, no significant difference was noted in the ratio among each group after statin administration. These findings were consistent with the findings of the analysis according to statin intensity.

CONCLUSION

In patients in the lowest TSH quartile of the normal TSH range, the CPK level decreased, and the proportion of normal CPK levels increased significantly after statin administration. However, similar changes were not observed in other TSH quartiles. Therefore, further studies are required to mechanistically confirm these conclusions.

Growth hormone replacement may influence the biological action of thyroid hormone on liver and bone tissue

OBJECTIVE

Growth hormone (GH) replacement alters the peripheral interconversion of thyroxine (T4) and triiodothyronine (T3). However, little is known about the clinical impact of these alterations. We aimed to compare changes observed in the serum T3:T4 ratio with known biological markers of thyroid hormone action derived from different peripheral tissues.

DESIGN

We prospectively studied twenty GH deficient men before and after GH replacement in a tertiary referral endocrine center. Serum biochemical measurements included insulin like growth factor-1 (IGF-1), thyroid hormones (free & total T3, free & total T4 and reverse T3) and TSH. Changes in thyroid hormone concentration were compared to alterations in hepatic and bone biomarkers of thyroid hormone action.

RESULTS

GH replacement provoked a decline in serum free T4 concentration (-1.09 ± 1.99 pmol/L; p = 0.02) and an increase in free T3 (+0.34 ± 0.15 pmol/L; p = 0.03); therefore, the free T3:free T4 ratio increased from 0.40 ± 0.02 to 0.47 ± 0.02 (p = 0.002). Sex hormone binding globulin (SHBG) level was unchanged. However, a decline in serum ferritin (-26.6 ± 8.5 ng/mL; p = 0.005) correlated with a fall in freeT4. Alterations in lipid profile, including a rise in large HDL sub-fractions and Lp (a) (+2.1 ± 21.1 nmol/L; p = 0.002) did not correlate with thyroid hormone levels. Significant increases were recorded in serum bone turnover markers - procollagen type 1 amino-terminal propeptide +57.4%; p = 0.0009, osteocalcin +48.6%; p = 0.0007; c-terminal telopeptides of type 1 collagen +73.7%; p = 0.002. Changes in bone formation markers occurred in parallel with fluctuations in thyroid hormone.

CONCLUSION

GH-induced alterations in the thyroid axis are associated with complex, tissue specific effects on thyroid hormone action. Modulation of bone turnover markers suggests that GH may improve the biological action of thyroid hormone on bone.

Effects of Thyroid Function on Phosphodiester Concentrations in Skeletal Muscle and Liver: An In Vivo NMRS Study

CONTEXT

Thyroid function is clinically evaluated by determination of circulating concentrations of thyrotropin (thyroid-stimulating hormone; TSH) and free thyroxine (fT4). However, a tissue-specific effector substrate of thyroid function is lacking. Energy-rich phosphorus-containing metabolites (PM) and phospholipids (PL) might be affected by thyroid hormone action and can be noninvasively measured by 31P nuclear magnetic resonance spectroscopy (NMRS).

OBJECTIVES

To measure the actions of peripheral thyroid hormones on PM and PL tissue concentrations.

DESIGN AND SETTING

A longitudinal, prospective pilot study was performed.

PARTICIPANTS

Nine patients with hyperthyroidism (HYPER) and 4 patients with hypothyroidism (HYPO) were studied at baseline and 3 months after treatment.

MAIN OUTCOME MEASURES

High-field 1H/31P NMRS was used to assess profiles of PM, PL, and flux through oxidative phosphorylase in liver and skeletal muscle, as well as ectopic tissue lipid content.

RESULTS

The concentrations of total skeletal muscle (m-) and hepatic (h-) phosphodiesters (PDE) and one of the PDE constituents, glycerophosphocholine (GPC), were lower in HYPER compared with HYPO (m-PDE: 1.4 ± 0.4 mM vs 7.4 ± 3.5 mM, P = 0.003; m-GPC: 0.9 ± 0.3 mM vs 6.7 ± 3.5 mM, P = 0.003; h-PDE: 4.4 ± 1.4 mM vs 9.9 ± 3.9 mM, P = 0.012; h-GPC: 2.2 ± 1.0 mM vs 5.1 ± 2.4 mM, P = 0.024). Both h-GPC (rho = -0.692, P = 0.018) and h-GPE (rho = -0.633, P = 0.036) correlated negatively with fT4. In muscle tissue, a strong negative association between m-GPC and fT4 (rho = -0.754, P = 0.003) was observed.

CONCLUSIONS

Thyroxine is closely negatively associated with the PDE concentrations in liver and skeletal muscle. Normalization of thyroid dysfunction resulted in a decline of PDE in hypothyroidism and an increase in hyperthyroidism. Thus, PDE might be a sensitive tool to estimate tissue-specific peripheral thyroid hormone action.

Serum Creatine Kinase in Patients with Neuromyelitis Optica Spectrum Disorder

OBJECTIVES

There have been reports of elevated serum creatine kinase (CK) and myopathy in patients with Neuromyelitis Optica Spectrum Disorder (NMOSD). Such findings have raised the possibility that myopathies may be a part of the spectrum of NMOSD. The incidence of elevated CK in NMOSD remains unknown. We sought to assess the potential association between hyperCKemia, myopathy, and NMOSD, and the potential role of screening for muscle involvement using serum CK.

METHODS

We reviewed records of all aquaporin 4 (AQP4) antibody-seropositive and seronegative NMOSD patients who had CK levels evaluated at two major academic medical centers.

RESULTS

Of 199 total NMOSD patients, CK levels were checked in 43, and elevated, on at least one occasion, in 4. In 1 patient, CK was elevated during an NMO exacerbation. A myopathic process occurring with NMOSD was suggested in 2 of 4 patients in the form of symptomatic complaint of myalgias and associated MRI signal change.

DISCUSSION

Unexplained hyperCKemia was found on one or more occasion in 4 of 43 tested NMOSD patients. Testing NMOSD patients for serum CK may reveal otherwise unsuspected myopathy. More formally powered, prospective assessment of the incidence and utility of CK in NMOSD is needed.

A Rare Case of Renal Impairment Caused by Primary Hypothyroidism

An association between hypothyroidism and renal impairment has rarely been reported in the literature. We describe a case of hypothyroidism that was associated with otherwise unexplained acute kidney impairment, which was reversed with treatment. A 21-year-old female patient presented to her family physician with myalgia, and preliminary investigations revealed an elevated level of creatine kinase and poor renal function. Primary hypothyroidism was diagnosed and no other apparent etiology for renal failure could be identified despite extensive investigations by the Nephrology Department. Notably, the patient’s renal impairment showed prompt resolution following thyroid hormone replacement.

Linear Analysis of Autonomic Activity and Its Correlation with Creatine Kinase-MB in Overt Thyroid Dysfunctions

Autonomic activity may be deranged in thyroid dysfunctions and may lead to cardiovascular morbidity and mortality. Myopathy is a common manifestation in thyroid disorders and may be associated with raised serum creatine kinase (CK). We hypothesized that cardiovascular abnormality in thyroid dysfunction may manifest as raised CK-MB. This study was designed to investigate the correlation of CK and its isoform CK-MB with thyroid profile and linear parameters of heart rate variability (HRV). The study was conducted on 35 hypothyroid and hyperthyroid patients each, and 25 age-matched healthy controls. Autonomic activity was assessed by simple short term 5-min HRV. Biochemical evaluation of serum thyroid profile, CK-NAC and CK-MB were estimated in all the subjects. Our results demonstrated low HRV in hypo- as well as hyperthyroid patients. We observed significantly higher serum CK levels in hypothyroid patients when compared to hyperthyroids and controls. However, no significant differences were observed in CK-MB levels in the three groups. Significant positive correlation of CK with TSH and negative correlation with some HRV parameters (LF power, HF power, total power, SDNN, RMSSD) was observed in hypothyroid patients. Whereas correlation of CK-MB with thyroid profile as well as HRV parameters was non-significant in all the groups. Based on the CK and CK-MB findings and their correlation, we conclude that the cardiovascular changes seen in thyroid dysfunctions may primarily be due to autonomic imbalance without apparent cardiac muscle involvement. Whereas, raised CK levels indicate predominantly skeletal muscle involvement in hypothyroid patients.

Impact of physical activity of individuals and creatine kinase on 99th percentiles of troponin I assays

Determination of cardiac troponin I (cTnI) is one central means for diagnosis of myocardial infarction. Assay performance of three troponin I assays was compared previously in a large reference population detecting sex-differences in the 99th percentile only for the Dimension Vista cTnI assay. The present study examined the underlying effects. Values for cTnI were reused. Creatine kinase (CK) activity was determined in 2358 samples from blood donors. Information on physical activity was evaluated from health questionnaires. Using quantile regression data were analysed to investigate the impact of sex, physical activity, and CK on the 99th percentile of the cTnI assay. We report significant sex-differences for the 99th percentile of cTnI. Physical activity was significantly associated with cTnI values. Strong association of CK activity with cTnI values was detected only in men. Adjustment for CK in quantile regression abolished sex-differences in the 99th percentile. Two other contemporary sensitive cTnI assays were not relevantly affected by physical activity or CK. Sex-differences in the 99th percentile for the Dimension Vista cTnI assay arise from a positive association between cTnI and physical activity and were abrogated when data were adjusted for CK activity. These findings should be taken into account when using this assay.

Developmental exposure to a commercial PBDE mixture: effects on protein networks in the cerebellum and hippocampus of rats

BACKGROUND

Polybrominated diphenyl ethers (PBDEs) are structurally similar to polychlorinated biphenyls (PCBs) and have both central (learning and memory deficits) and peripheral (motor dysfunction) neurotoxic effects at concentrations/doses similar to those of PCBs. The cellular and molecular mechanisms for these neurotoxic effects are not fully understood; however, several studies have shown that PBDEs affect thyroid hormones, cause oxidative stress, and disrupt Ca2+-mediated signal transduction. Changes in these signal transduction pathways can lead to differential gene regulation with subsequent changes in protein expression, which can affect the development and function of the nervous system.

OBJECTIVE

In this study, we examined the protein expression profiles in the rat cerebellum and hippocampus following developmental exposure to a commercial PBDE mixture, DE-71.

METHODS

Pregnant Long-Evans rats were dosed perinatally with 0 or 30.6 mg/kg/day of DE-71 from gestation day 6 through sampling on postnatal day 14. Proteins from the cerebellum and hippocampus were extracted, expression differences were detected by two-dimensional difference gel electrophoresis, and proteins were identified by tandem mass spectrometry. Protein network interaction analysis was performed using Ingenuity® Pathway Analysis, and the proteins of interest were validated by Western blotting.

RESULTS

Four proteins were significantly differentially expressed in the cerebellum following DE-71 exposure, whereas 70 proteins were significantly differentially expressed in the hippocampus. Of these proteins, 4 from the cerebellum and 47 from the hippocampus, identifiable by mass spectrometry, were found to have roles in mitochondrial energy metabolism, oxidative stress, apoptosis, calcium signaling, and growth of the nervous system.

CONCLUSIONS

Results suggest that changes in energy metabolism and processes related to neuroplasticity and growth may be involved in the developmental neurotoxicity of PBDEs.

Comparison of pre- and post-levothyroxine high-sensitivity c-reactive protein and fetuin-a levels in subclinical hypothyroidism

OBJECTIVE

The objective of this trial was to determine the levels of inflammatory markers, high-sensitivity C-reactive protein and fetuin-A pre- and post-levothyroxine treatment in cases of subclinical hypothyroidism.

MATERIALS AND METHODS

A total of 32 patients with a diagnosis of subclinical hypothyroidism and a control group of 30 healthy individuals were tested for high-sensitivity C-reactive protein and fetuin-A, followed by the administration of 50 µg of levothyroxine in the patient group for 3 months. During the post-treatment stage, high-sensitivity C-reactive protein and fetuin-A levels in the patient group were re-assessed and compared with pre-treatment values.

RESULTS

Pre-treatment levels of both high-sensitivity C-reactive protein and fetuin-A were observed to be higher in the patient group than in the control group. The decrease in high-sensitivity C-reactive protein levels during the post-treatment stage was not statistically significant. However, the decrease observed in post-treatment fetuin-A levels was found to be statistically significant.

CONCLUSION

The decrease in fetuin-A levels in subclinical hypothyroidism cases indicates that levothyroxine treatment exerts anti-inflammatory and anti-apoptotic effects. Although the decrease in high-sensitivity C-reactive protein levels was statistically non-significant, it is predicted to reach significance with sustained treatment.

Endobiogeny: a global approach to systems biology (part 2 of 2)

ENDOBIOGENY AND THE BIOLOGY OF FUNCTIONS ARE BASED ON FOUR SCIENTIFIC CONCEPTS THAT ARE KNOWN AND GENERALLY ACCEPTED: (1) human physiology is complex and multifactorial and exhibits the properties of a system; (2) the endocrine system manages metabolism, which is the basis of the continuity of life; (3) the metabolic activity managed by the endocrine system results in the output of biomarkers that reflect the functional achievement of specific aspects of metabolism; and (4) when biomarkers are related to each other in ratios, it contextualizes one type of function relative to another to which is it linked anatomically, sequentially, chronologically, biochemically, etc.

Pulmonary oxygen uptake kinetics during exercise in subclinical hypothyroidism

BACKGROUND

Patients with subclinical hypothyroidism (SCH) have lower exercise tolerance, but the impact on oxygen uptake (VO2) kinetics is unknown. This study evaluated VO2 kinetics during and after a constant load submaximal exercise in SCH.

METHODS

The study included 19 women with SCH (thyrotropin (TSH)=6.87±2.88 μIU/mL, free thyroxine (fT4)=0.97±0.15 ng/dL) and 19 controls (TSH=2.29±0.86 μIU/mL, T4=0.99±0.11 ng/dL) aged between 20 and 55 years. Ergospirometry exercise testing was performed for six minutes with a constant load of 50 W, followed by six minutes of passive recovery. The VO2 kinetics was quantified by the mean response time (MRT), which is the exponential time constant and approximates the time needed to reach 63% of change in VO2 (ΔVO2). The O2 deficit-energy supplied by anaerobic metabolism at the onset of exercise-and O2 debit-extra energy demand during the recovery period-were calculated by the formula MRT×ΔVO2. Values are mean±standard deviation.

RESULTS

In the rest-exercise transition, patients with SCH showed slower VO2 kinetics (MRT=47±8 sec vs. 40±6 sec, p=0.004) and a higher oxygen deficit (580±102 mL vs. 477±95 mL, p=0.003) than controls respectively. In the exercise-recovery transition, patients with SCH also showed slower VO2 kinetics (MRT=54±6 sec vs. 44±6 sec, p=0.001) and a higher oxygen debit (679±105 mL vs. 572±104 mL, p=0.003). The VO2 kinetics showed a significant correlation with TSH (p<0.05).

CONCLUSIONS

This study demonstrates that women with SCH have the slowest VO2 kinetics in the onset and recovery of a constant-load submaximal exercise and highlights that this impairment is already manifest in the early stage of the disease.

Amiodarone-induced thyroid dysfunction

Amiodarone is an effective medication for the treatment of cardiac arrhythmias. Originally developed for the treatment of angina, it is now the most frequently prescribed antiarrhythmia drug despite the fact that its use is limited because of potential serious side effects including adverse effects on the thyroid gland and thyroid hormones. Although the mechanisms of action of amiodarone on the thyroid gland and thyroid hormone metabolism are poorly understood, the structural similarity of amiodarone to thyroid hormones, including the presence of iodine moieties on the inner benzene ring, may play a role in causing thyroid dysfunction. Amiodarone-induced thyroid dysfunction includes amiodarone-induced thyrotoxicosis (AIT) and amiodarone-induced hypothyroidism (AIH). The AIT develops more commonly in iodine-deficient areas and AIH in iodine-sufficient areas. The AIT type 1 usually occurs in patients with known or previously undiagnosed thyroid dysfunction or goiter. The AIT type 2 usually occurs in normal thyroid glands and results in destruction of thyroid tissue caused by thyroiditis. This is the result of an intrinsic drug effect from the amiodarone itself. Mixed types are not uncommon. Patients with cardiac disease receiving amiodarone treatment should be monitored for signs of thyroid dysfunction, which often manifest as a reappearance of the underlying cardiac disease state. When monitoring patients, initial tests should include the full battery of thyroid function tests, thyroid-stimulating hormone, thyroxine, triiodothyronine, and antithyroid antibodies. Mixed types of AIT can be challenging both to diagnose and treat and therapy differs depending on the type of AIT. Treatment can include thionamides and/or glucocorticoids. The AIH responds favorably to thyroid hormone replacement therapy. Amiodarone is lipophilic and has a long half-life in the body. Therefore, stopping the amiodarone therapy usually has little short-term benefit.

Aroclor 1254, a developmental neurotoxicant, alters energy metabolism- and intracellular signaling-associated protein networks in rat cerebellum and hippocampus

The vast literature on the mode of action of polychlorinated biphenyls (PCBs) indicates that PCBs are a unique model for understanding the mechanisms of toxicity of environmental mixtures of persistent chemicals. PCBs have been shown to adversely affect psychomotor function and learning and memory in humans. Although the molecular mechanisms for PCB effects are unclear, several studies indicate that the disruption of Ca(2+)-mediated signal transduction plays significant roles in PCB-induced developmental neurotoxicity. Culminating events in signal transduction pathways include the regulation of gene and protein expression, which affects the growth and function of the nervous system. Our previous studies showed changes in gene expression related to signal transduction and neuronal growth. In this study, protein expression following developmental exposure to PCB is examined. Pregnant rats (Long Evans) were dosed with 0.0 or 6.0mg/kg/day of Aroclor-1254 from gestation day 6 through postnatal day (PND) 21, and the cerebellum and hippocampus from PND14 animals were analyzed to determine Aroclor 1254-induced differential protein expression. Two proteins were found to be differentially expressed in the cerebellum following PCB exposure while 18 proteins were differentially expressed in the hippocampus. These proteins are related to energy metabolism in mitochondria (ATP synthase, sub unit β (ATP5B), creatine kinase, and malate dehydrogenase), calcium signaling (voltage-dependent anion-selective channel protein 1 (VDAC1) and ryanodine receptor type II (RyR2)), and growth of the nervous system (dihydropyrimidinase-related protein 4 (DPYSL4), valosin-containing protein (VCP)). Results suggest that Aroclor 1254-like persistent chemicals may alter energy metabolism and intracellular signaling, which might result in developmental neurotoxicity.

Low-normal or high-normal thyrotropin target levels during treatment of hypothyroidism: a prospective, comparative study

BACKGROUND

Recent literature advocates the decrease of the upper limit of the normal thyrotropin (TSH) reference range. The objective of this study was to determine whether treated hypothyroid patients maintained within a low-normal TSH range (0.4-2.0 mIU/L) have better clinical outcomes than those maintained within a high-normal TSH range (2.0-4.0 mIU/L).

METHODS

The study was performed in a thyroid outpatient clinic of a tertiary hospital. This was a prospective, interventional study. Forty-two participants with newly diagnosed overt primary hypothyroidism were paired in two groups: group 1 (n=20), low-normal target TSH; group 2 (n = 22), high-normal target TSH. Levothyroxine was initiated, and dose was adjusted to achieve and sustain the target TSH value during the study period. After the target TSH was reached, participants were evaluated every 3 months for thyroid function, serum lipid profile, resting energy expenditure (REE), body composition, and bone mineral density, for 12 months.

RESULTS

Nineteen patients in group 1 and 16 in group 2 completed the study. In the whole-group analysis, total cholesterol (p = 0.01), low-density lipoprotein cholesterol (p = 0.004), and triglycerides (p < 0.001) decreased after treatment, whereas REE per kilogram of lean body mass (p = 0.001) and total fat body mass (p =0.02) increased. Group 1 patients had a significantly higher relative increase in REE (+7.1% ± 11.3% vs. +3.6% ± 15.1%, p = 0.02). There was no difference between the groups in the other variables.

CONCLUSIONS

Despite recent trends toward lowering the upper limit of normal TSH range, the results of this 12-month study provided no substantial clinical evidence to corroborate that treatment of primary hypothyroidism should aim at maintaining TSH levels in a low-normal range

Effects of thyroid dysfunction on lipid profile

Thyroid dysfunction has a great impact on lipids as well as a number of other cardiovascular risk factors. Hypothyroidism is relatively common and is associated with an unfavorable effect on lipids. Substitution therapy is beneficial for patients with overt hypothyroidism, improving lipid profile. However, whether subclinical hypothyroidism should be treated or not is a matter of debate. On the other hand, hyperthyroidism can be associated with acquired hypocholesterolemia or unexplained improvement of lipid profile. Overall, thyroid dysfunction should be taken into account when evaluating and treating dyslipidemic patients.

Two cases of statin-induced myopathy caused by induced hypothyroidism

OBJECTIVE

To present information regarding the potential danger of performing levothyroxine withdrawal radioiodine scans and treatment in patients with thyroid cancer who are concurrently taking lipid-lowering agents.

METHODS

We review the clinical history, serial laboratory data, and radiologic findings in 2 patients with multifocal papillary carcinoma of the thyroid.

RESULTS

Both study patients had substantial elevations of muscle enzymes or myopathies (or both) when they were withdrawn from levothyroxine therapy, during treatment with lipid-lowering agents, in preparation for radioiodine scanning and treatment.

CONCLUSION

Extreme caution should be exercised when levothyroxine therapy is withdrawn from patients taking lipid-lowering agents. Such patients should be monitored very closely or, when appropriate, recombinant human thyroid-stimulating hormone injections should be used rather than levothyroxine withdrawal in this setting.

[Thyroid dysfunction in women with suspected fibromyalgia]

BACKGROUND AND OBJECTIVE

Due to its prevalence, morbidity, and frequency rate, fibromyalgia (FM) represents a health problem and produces high healthcare resource utilization. Serum thyrotropin (TSH) measurement is recommended as a first-line laboratory test to exclude hypothyroidism as a cause of FM syndrome. The aim of this study was to analyze the prevalence of thyroid dysfunction (TD), the frequency of TSH measurement, the effect of levothyroxine treatment, and whether screening for TD is justified in women with suspected FM.

PATIENTS AND METHODS

A cross-sectional descriptive study was performed in 400 consecutive female outpatients with suspected FM and in 384 controls from January 2001 to October 2004. TSH measurement was used as the first line test to detect TD.

RESULTS

The prevalence of TD in patients with suspected FM (40/400; 10%; 95% CI: 7-13%) and controls was similar (46/384; 12%; 95% CI: 9-15%). No differences were found in the types and grades of TD. The prevalence of TD was higher in patients with suspected FM and connective tissue diseases (12%) than in those without these diseases (5%). The most frequent TD was subclinical hypothyroidism (5.5% in suspected FM and 6.7% in controls), and in 93% of these cases TSH concentrations were <10 mIU/L. FM persisted in all women with hypothyroidism even after euthyroidism was achieved with levothyroxine. A total of 870 TSH determinations were performed in 360 euthyroid patients with suspected FM.

CONCLUSIONS

The prevalence of TD in women with suspected FM does not differ from that in the general population. Screening for TD does not appear to be justified in women without diseases that increase their risk. In many cases the request for thyroid function tests is excessive. Treatment for hypothyroidism does not affect FM.

The clinical significance of subclinical thyroid dysfunction

Subclinical thyroid disease (SCTD) is defined as serum free T(4) and free T(3) levels within their respective reference ranges in the presence of abnormal serum TSH levels. SCTD is being diagnosed more frequently in clinical practice in young and middle-aged people as well as in the elderly. However, the clinical significance of subclinical thyroid dysfunction is much debated. Subclinical hyper- and hypothyroidism can have repercussions on the cardiovascular system and bone, as well as on other organs and systems. However, the treatment and management of SCTD and population screening are controversial despite the potential risk of progression to overt disease, and there is no consensus on the thyroid hormone and thyrotropin cutoff values at which treatment should be contemplated. Opinions differ regarding tissue effects, symptoms, signs, and cardiovascular risk. Here, we critically review the data on the prevalence and progression of SCTD, its tissue effects, and its prognostic implications. We also examine the mechanisms underlying tissue alterations in SCTD and the effects of replacement therapy on progression and tissue parameters. Lastly, we address the issue of the need to treat slight thyroid hormone deficiency or excess in relation to the patient's age.

Avaliação clínica e da função muscular em pacientes com hipotireoidismo subclínico

Alguns sintomas e sinais de hipotireoidismo, bem como alterações laboratoriais, podem estar presentes no hipotireoidismo subclínico (HS). Este trabalho avalia a prevalência de sintomas e sinais de hipotireoidismo e alterações músculo-esqueléticas em pacientes com HS (n= 57) comparado a um grupo controle sem disfunção tireoideana (n= 37). Baseado na presença de sintomas e sinais de hipotireoidismo, os participantes receberam pontuação específica (escore clínico). A força muscular foi aferida pelo teste muscular manual e por dinamômetro de cadeira e a força inspiratória por manovacuômetro. Os níveis de hormônios tireoideanos e enzimas musculares foram dosados. O grupo HS apresentou escore mais elevado (p< 0,01), maior freqüência das queixas de mialgia e fraqueza (p< 0,05) e redução de força das cinturas escapular e pélvica (p< 0,05). Os níveis médios de T4 livre foram menores no HS (p< 0,001). Os resultados sugerem que a presença de sintomas e sinais de disfunção tireoideana e níveis de T4 livre na faixa inferior da normalidade no HS possam estar relacionados e devem ser valorizados na decisão de iniciar LT4.

Acute changes in clinical parameters and thyroid function peripheral markers following L-T4 withdrawal in patients totally thyroidectomized for thyroid cancer

After total thyroidectomy, differentiated thyroid cancer (DTC) patients have to undergo L-T4 withdrawal for measuring serum thyroglobulin and 131I whole-body scan (131I WBS) to evaluate residual/recurrent malignant disease. The aim of the present work was to study in these patients the effects of acute thyroid hormone deficiency on various target organs and tissues. Clinical parameters and thyroid function peripheral markers were evaluated in 20 DTC patients, both before and after L-T4 withdrawal. A 24-h urine collection, a fasting blood sample for laboratory examinations, a clinical score for hypothyroidism and cardiovascular, neurological and neuropsychological evaluations were carried out. After L-T4 withdrawal, the clinical score significantly increased, as well as total cholesterol, triglycerides, creatine kinase, lactate dehydrogenase, aspartate aminotransferase and alanine aminotransferase, whereas SHBG, osteocalcin and urine hydroxyproline levels significantly decreased. The acute thyroid hormone deficiency caused a systolic dysfunction of the left ventricle associated with an increase in systemic vascular resistance without cardiac contractility alterations. A significant increase in the left ventricular mass and thickness was also observed. Carpal tunnel syndrome appeared in 30% of patients and a significant reduction in the immediate auditive memorization and in attentive performance was also detected. These observations indicate that acute hypothyroidism causes significant clinical alterations of peripheral tissue function. In the follow-up of DTC patients, therefore, L-T4 withdrawal procedure should be restricted to cases where the cost/benefit ratio is favorable. Alternative procedures, such as the use of recombinant human TSH, should be used whenever possible.

Effects of levothyroxine treatment on biochemical and hemostasis parameters in patients with hypothyroidism

OBJECTIVE

The aims of the study were to evaluate the disturbances in the coagulation system in patients with overt hypothyroidism (OH), to assess the effects of levothyroxine (LT4) on the coagulation parameters, and to determine whether subclinical hypothyroidism (SH) affects concentrations of coagulation markers and several biochemical parameters, thereby supporting early substitution.

DESIGN

The study included 15 patients with SH (TSH levels 5-10 mU/l), 15 patients with OH and 15 euthyroid controls.

METHODS

Blood urea nitrogen, creatinine, creatine phosphokinase, aspartate aminotransferase, lactate dehydrogenase, total-cholesterol, high density lipoprotein-cholesterol, low density lipoprotein-cholesterol and triglyceride levels, and bleeding time, prothrombin time (PT), activated partial thromboplastin time (APTT), factor VIII activity, von Willebrand factor activity (vWF), platelet count and clotting time were evaluated just before and three months after the maintenance of euthyroidism with LT4 treatment.

RESULTS

Factor VIII and vWF activities were lower in patients with SH than in controls (P < 0.01). Increased bleeding time, PT, APTT and clotting time and decreased factor VIII activity and vWF activity were observed in patients with OH when compared with controls. Bleeding time, PT, APTT and clotting time decreased and factor VIII activity, vWF and platelet count increased after LT4 in patients with OH. Increases in factor VIII activity and vWF (P < 0.01) were detected also in the SH group with treatment.

CONCLUSIONS

OH is associated with significant abnormalities in clotting parameters which are reversed by LT4. In contrast, SH is associated with minor changes in factor VIII activity and vWF which are reversible by LT4. Serum lipids and other measured parameters are not improved by LT4 in patients with TSH < 10 mU/l and these data fail to demonstrate a need to treat such patients.

Serum creatine kinase levels in overt and subclinical hypothyroidism

The aims of this prospective study were to determine serum levels of creatine kinase (CK) in overt and subclinical hypothyroidism; to investigate the change in CK levels with treatment; and to evaluate the relationship between free triiodsothyronine (FT3), free thyroxine (FT4), and thyrotropin (TSH) levels and the degree of skeletal muscle involvement, as determined by serum CK levels. Patients with hypothyroidism presenting to our endocrinology clinic were eligible for inclusion in this study. Patients with other causes of CK elevation were excluded. We included 28 patients (25 women and 3 men, ages 41.75 +/- 13.65 years) with overt hypothyroidism, 38 patients (37 women, 1 man, ages 40.55 +/- 10.48 years) with subclinical hypothyroidism, and 30 age- and gender-matched controls (27 women, 3 men, ages 40.81 +/- 11.20 years) in the study. Serum levels of TSH, FT4, FT3, and CK were measured in all subjects. CK elevation was found in 16 patients (57%) with overt hypothyroidism and in 4 patients (10%) with subclinical hypothyroidism. Although a statistically significant elevation of CK levels was found in patients with overt hypothyroidism when compared with patients with subclinical hypothyroidism and controls (p = 0. 0001, p = 0. 01, respectively), no difference was found between the subclinical hypothyroidism and control groups (p = 0.14). In hypothyroid (overt and subclinical) patients, a positive correlation was found between CK and TSH (r = 0.432; p = 0.04), and a negative correlation between CK and FT3 (r = - 0.556; p = 0.002) and between CK and FT4 (r =0.448; p = 0.04). CK levels decreased to normal levels after thyroid function normalized with treatment. In conclusion, skeletal muscle is affected by hypothyroidism more profoundly in cases of overt hypothyroidism, less so when subclinical hypothyroidism is present.

Hepatic iodothyronine deiodinase type 1 activity is decreased in two ΔF508 cystic fibrosis mouse models

BACKGROUND

Abnormal thyroid status has been reported in cystic fibrosis (CF) patients, and this can possibly be correlated to neuromuscular symptoms. Iodothyronine deiodinase type 1 (D1) activity is an important determinant of thyroid status, and we chose to investigate D1 activity in CF liver.

METHODS

We have measured hepatic D1 activities in two DeltaF508 CF mouse models.

RESULTS

Hepatic D1 activity was significantly reduced by 31% to 48% in homozygous DeltaF508 mice compared with wild-type genotypes.

CONCLUSIONS

A decreased hepatic D1 activity could be the biochemical basis of some of the abnormal thyroid parameters observed in cystic fibrosis patients.

Hypothyroidism

Hypothyroidism is common, potentially serious, often clinically overlooked, readily diagnosed by laboratory testing, and eminently treatable. The condition is particularly prevalent in older women, in whom autoimmune thyroiditis is common. Other important causes include congenital thyroid disorders, previous thyroid surgery and irradiation, drugs such as lithium carbonate and amiodarone, and pituitary and hypothalamic disorders. Worldwide, dietary iodine deficiency remains an important cause. Hypothyroidism can present with nonspecific constitutional and neuropsychiatric complaints, or with hypercholesterolaemia, hyponatraemia, hyperprolactinaemia, or hyperhomocysteinaemia. Severe untreated hypothyroidism can lead to heart failure, psychosis, and coma. Although these manifestations are neither specific nor sensitive, the diagnosis is confirmed or excluded by measurements of serum thyrotropin and free thyroxine. Thyroxine replacement therapy is highly effective and safe, but suboptimal dosing is common in clinical practice. Patient noncompliance, drug interactions, and pregnancy can lead to inadequate treatment. Iatrogenic thyrotoxicosis can cause symptoms, and, even when mild, provoke atrial fibrillation and osteoporosis. We summarise present understanding of the history, epidemiology, pathophysiology, and clinical diagnosis and management of hypothyroidism.

Renal failure and acquired hypothyroidism

The effects of thyroid metabolism on renal function in children are barely referred to in the literature. Primary hypothyroidism is known to be associated with a consistent elevation in serum creatinine levels. This is essentially because of the hypodynamic state that occurs in hypothyroidism, leading to a reduced glomerular filtration rate and hypercreatinemia. A teenager who developed renal failure due to primary hypothyroidism is reported. He displayed diverse serum biochemistry anomalies with an unremarkable physical examination. Thyroxine replacement therapy completely restored the euthyroid state and renal function. We propose, in accordance with other authors, measurement of thyrotropin levels in patients with hypercreatinemia.

Alteration of serum enzymes in primary hypothyroidism

In order to study the relationships between serum enzymes and the degree of hypothyroidism, 114 patients with primary hypothyroidism aged from 7 to 65 years were investigated. Forty one percent of patients exhibited normal levels of serum enzymes, while 59% had high levels either alone or in combination. The frequency of enzyme elevation was as follows: creatine kinase: 37%, aspartate aminotransferase: 35%, alanine aminotransferase: 29%, amylase: 15%, alkaline phosphatase: 3%. No significant correlation between thyroid stimulating hormone and serum enzyme levels was observed. This was due to highly variable release of enzymes from cells resulting presumably from individual metabolic set-point. Replacement therapy with thyroxine resulted in remarkable lowering of creatine kinase not only from high level to normal as early as 3 weeks even before normalization of thyroid stimulating hormone, but also from high normal to low normal level. The elevation of amylase and its response to thyroxine is being reported for the first time.

Serum creatine kinase elevation in a medical department

Serum creatine kinase (CK) levels are diagnostic markers for acute myocardial infarction. Many other causes however, including neuromuscular disorders, may induce serum CK elevation as well. Aim of the study was to investigate the prevalence of potential causes for serum CK elevation in a medical department. In particular we were interested in the recognition of patients in whom serum CK elevation was due to a neuromuscular disorder. Included in this prospective study were 100 consecutive patients in whom the CK level, determined at admission, was increased (> 70 IU/l in female, > 80 IU/l in male patients). After admission we looked for the presence of causes known to induce CK elevation. Patients with no potential cause for CK elevation were invited for follow-up investigations three months later. If no potential cause could be found and if CK was elevated again on this occasion, the patient was referred for a comprehensive neurological investigation. The prevalence of patients with CK elevation was 11.2%. The 100 patients (44 female, 56 male) were aged from 23 to 94 (mean 67) years. In 95% CK elevation was only up to 500 IU/l. The most frequent cause for serum CK elevation was acute myocardial infarction in 32%. Further frequent causes were drug intake (32%), fall (24%), haematoma (17%), intramuscular injection (16%) and malignancy (11%). In 61% of the cases at least two potential causes for serum CK elevation could be detected. Neuromuscular disorders were found in only 2%. This study shows that serum CK elevation occurs in 11% of patients admitted to a medical department and can be explained by acute myocardial infarction in only 32%. In almost two thirds of the patients, more than one potential cause for serum CK elevation can be found thus making CK elevation a rather unspecific finding. Neuromuscular disorders are rarely found as a cause of serum CK elevation in a medical department.

When to treat mild hypothyroidism

The availability and wide acceptance of TSH assays for primary assessment of thyroid function has led to the recognition that mild thyroid hormone deficiency is characterized by elevation of the serum TSH concentration despite a normal free thyroxine level. Other conditions can also cause isolated serum TSH elevation, and these conditions can be distinguished from mild thyroid failure usually based-on clinical and circumstantial observations alone. Thyroxine treatment of patients with mild hypothyroidism has been shown in most, but not all, clinical trials to lower atherogenic lipid levels and relieve certain somatic and neuropsychiatric symptoms. Such treatment also prevents the progression to overt hypothyroidism, which is particularly likely in patients who are older, who have circulating thyroid autoantibodies, or who have a serum TSH greater than 10 mU/L. After the optimal thyroxine dose has been defined, long-term monitoring of patients with an annual clinical evaluation and serum TSH measurement is appropriate. The high prevalence of mild hypothyroidism, particularly in older women, and its subtle clinical presentation have led some authorities to recommend a low threshold for case-finding or routine population screening for the disorder.