[Euthyroid sick syndrome: recent physiopathologic findings]

Gender differences in the effects of organochlorines, mercury, and lead on thyroid hormone levels in lakeside communities of Quebec (Canada)

Environmental chemicals can disrupt endocrine balance and in particular thyroid hormone (TH) homeostasis. However, studies differ with respect to thyroid profile changes and gender differences are rarely examined. This study investigated the THs, triodothyronine (T3), thyroxine (T4), and thyroid stimulating hormone (TSH), in relation to serum organochlorines (OCs), bioindicators of mercury (Hg) and blood lead (Pb) in 211 freshwater fish consumers (124 men and 87 women) from two communities in Canada. Thyroid hormones were within the normal range and the bioindicators of exposure were low compared to other reports on fish consumers. Stratified analysis showed that for women, serum T3 concentrations were negatively related to serum concentrations of PCB 138, PCB 153, the non-coplanar congeners, Arochlor 1260, and SigmaPCB, as well as p,p'-DDE. No relations were observed between T4 and any of the chemicals measured, but TSH was negatively related to blood Pb. For men, serum T4 was inversely related to PCB 138, non-ortho-substituted (dioxin-like) PCBs and SigmaPCB. A significant positive relationship was observed between serum TSH and different PCB congeners (PCB 138, PCB 180, non-coplanar congeners, mono-ortho coplanar congeners, dioxin-like PCBs), as well as SigmaPCB. Serum TSH increased with hair and blood Hg concentrations and was highest among those in the highest 50th percentile for both Hg and dioxin-like PCB congeners compared to the others. No associations were observed for T3 in men. These findings suggest that even at low concentrations, these environmental contaminants can interfere with thyroid status and effects may differ by gender.

Manifestations et risques cardiovasculaires des dysthyroïdies infracliniques

PURPOSE

To clarify the importance of cardiovascular symptoms and risks in subclinical dysthyroidism in order to define the best way of treatment and follow-up.

CURRENT KNOWLEDGE AND KEY POINTS

Subclinical dysthyroidism is defined by abnormal circulating TSH values in face and normal free thyroid hormones levels, in asymptomatic individuals. If the cardiovascular effects of overt hyperthyroidism are well documented, the relation between subclinical dysthyroidism and the heart is not well established. Subclinical hyperthyroidism may be caused by the same thyroid disorders that results in overt hyperthyroidism, but the most common cause is excessive dosage in levothyroxine. The most frequent cardias complication of subclinical hyperthyroidism is atrial fibrillation. Recently minimal alterations of myocardial function have also been described. In most patients, one tries to return to euthyroidism in order to prevent cardiovascular complications. Subclinical hypothyroidism is 3 to 10 times more frequent, especially in women after 60 years. Subtle modifications of cardiac function and lipid metabolism and an increased risk of atherosclerosis have been described in this condition. There is still debate about the decision to treat or not to treat these patients.

FUTURE PROSPECTS AND PROJECTS

Until now, treatment of subclinical dysthyroidism is mainly based upon experiences and convictions to physicians. Prospective studies are necessary to assess the true benefits and risks of either early treatment or therapeutic abstention with regular clinical and biological follow up. In such studies, patients should be separated according to age and the nature (endogenous or exogenous) of dysthyroidism.

Dopamine infusion and hypothyroxinaemia in very low birth weight preterm infants

The purpose of this study was to assess the relationship between transient hypothyroxinaemia of prematurity (THOP) in very low birth weight newborns and dopamine administration. A total of 172 newborns was enrolled in a prospective observational study and divided into three groups: group A included newborns who were never treated with dopamine; group B were infants in whom dopamine treatment was discontinued for at least 6 h before the congenital hypothyroidism screening and group C included infants who were given dopamine during the screening. Among those newborns given dopamine, the THOP incidence was higher (11.6% in group A; 53.8% in group B; 89.3% in group C), and the vales of TSH (1.67+/-2.32 microU/ml in group A; 1.29+/-1.74 microU/ml in group B; 0.89+/-1.34 microU/ml in group C) and thyroxine (6.1+/-2.2 microg/dl in group A; 3.9+/-1.9 microg/dl in group B; 2.4+/-1.4 microg/dl in group C) were significantly lower. These differences were further confirmed even after gestational age stratification and mathematical correction for differences in clinical conditions. The effects of dopamine appear to be dose-dependent.

CONCLUSION

Even if it cannot be excluded that reduced thyroid stimulating hormone and thyroxine concentrations are caused by non-thyroidal illness, the results suggest that the infusion of dopamine reduces the thyroid stimulating hormone and thyroxine levels in very low birth weight newborns.

Evaluation of growth and hormonal status in patients referred to the International Fanconi Anemia Registry

OBJECTIVES

1) To determine the extent of short stature in patients with Fanconi anemia (FA); 2) to determine the extent and nature of endocrinopathy in FA; 3) to assess the impact on height of any endocrinopathies in these patients; and 4) to study the correlation, if any, between height, endocrinopathy, and FA complementation group.

STUDY DESIGN

Fifty-four patients with FA, 30 males and 24 females from 47 unrelated families, were prospectively evaluated in a Pediatric Clinical Research Center. The patients ranged in age from 0.1-31.9 years, with the mean age at assessment 8.6 years.

RESULTS

Endocrine abnormalities were found in 44 of the 54 FA patients tested (81%), including short stature, growth hormone (GH) insufficiency, hypothyroidism, glucose intolerance, hyperinsulinism, and/or overt diabetes mellitus. Twenty-one of 48 (44%) participants had a subnormal response to GH stimulation; 19 of 53 (36%) had overt or compensated hypothyroidism, while 8 of 40 participants had reduced thyroid-hormone binding. Two patients were diabetic at the time of study; impaired glucose tolerance was found in 8 of 40 patients (25%), but most surprisingly, hyperinsulinemia was present in 28 of 39 (72%) participants tested. Significantly, spontaneous overnight GH secretion was abnormal in all patients tested (n = 13). In addition, participants demonstrated a tendency toward primary hypothyroidism with serum tetraiodothyronine levels at the lower range of normal, while also having thyrotropin (thyroid-stimulating hormone) levels at the high end of normal. Sixteen patients were assigned to FA complementation group A, (FA-A), 12 to FA-C, and 5 to FA-G; 10 of the 12 participants in FA-C were homozygous for a mutation in the intron-4 donor splice site of the FANCC gene. Patients in groups FA-A and FA-G were relatively taller than the group as a whole (but still below the mean for the general population), whereas those in FA-C had a significantly reduced height for age. GH response to stimulation testing was most consistently normal in participants from FA-G, but this did not reach statistical significance. The tendency toward hypothyroidism was more pronounced in participants belonging to complementation groups FA-C and FA-G, whereas insulin resistance was most evident in patients in FA-G, and least evident in those in FA-C. Short stature was a very common finding among the patients with a mean height >2 standard deviations below the reference mean (standard deviation score: -2.35 +/- 0.28). Patients with subnormal GH response and those with overt or compensated hypothyroidism were shorter than the group with no endocrinopathies. The heights of those participants with glucose or insulin abnormalities were less severely affected than those of normoglycemic, normoinsulinemic participants, although all were significantly below the normal mean. The mean height standard deviation score of patients with entirely normal endocrine function was also >2 standard deviations below the normal mean, demonstrating that short stature is an inherent feature of FA.

CONCLUSION

Endocrinopathies are a common feature of FA, primarily manifesting as glucose/insulin abnormalities, GH insufficiency, and hypothyroidism. Although short stature is a well-recognized feature of FA, 23 patients (43%) were within 2 standard deviations, and 5 of these (9% of the total) were actually above the mean for height for the general population. Those patients with endocrine dysfunction are more likely to have short stature. These data indicate that short stature is an integral feature of FA, but that superimposed endocrinopathies further impact on growth. The demonstration of abnormal endogenous GH secretion may demonstrate an underlying hypothalamic-pituitary dysfunction that results in poor growth.