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In the so-called non-thyroidal illness syndrome serum T3 is lowered and
in severe cases even T4 parameters, whereas serum TSH is mostly normal.
This abnormal profile is caused by acute and chronic illness, not related
to the thyroid gland, energy restriction, and by the use of some drugs.
To investigate why serum TSH is not elevated, despite lower values of T3
and sometimes T4, Everts et al., Rotterdam, The Netherlands, tested the
effects of tetraiodothyroacetic acid (TETRAC) on its TSH suppressive effect
in cultures of rat pituitaries, as TETRAC levels are increased in non-thyroidal
illness. They found that TETRAC might have indeed a TSH suppressive effect
in combination with triiodethyroacetic acid (TRIAC) as they have already
previously reported. The same group additionally reported that also interleukin-I
beta (IL-1i) that is also produced in increased amounts in non-thyroidal
illness may have an inhibitory effect on TSH secretion as well. There is
controversy in the literature about the efficacy of T3 treatment in cardiac
surgery.
Klemperer et al., New York, NY, USA, administered either T3 or placebo to 71 and 72 patients respectively, who underwent cardiopulmonary bypass. Although cardiac performance was enhanced by T3 treatment, overall mortality was not different in the two groups (see also Klemperer et al., New Engl J Med 333, 1522, 1995 and Utiger, New Engl J Med 333, 1562,1995). Boelen et al., Amsterdam, The Netherlands, studied the effects of cytokines on the induction of the low T3 syndrome (synonymous for non-thyroidal illness syndrome). They could not find a significant effect of depletion of liver macrophages (that produce cytokines) in mice, when non-thyroidal illness was induced by injection of bacterial endotoxin. Despite depletion of this type of cells, the low T3 syndrome was still produced. The same group also published that in their studies in patients with non-thyroidal illness there was only a slight negative relation between serum T3 and serum IL-8 but not with IL-10 or INF gamma. From these studies the authors concluded that cytokines do not play an important part in the induction of non-thyroidal illness syndrome. Wang et al., Loma Linda and San Juan Capistrano, CA, USA, induced low serum total T4 and total and free T3 levels, but normal free T4 concentrations after administration of the non-steroidal anti-inflammatory drug salsalate. They also find a decrease in serum TSH (despite low serum total and free T3) and explain absence of increase in TSH on the basis of displacement of T4 form serum binding proteins by this drug. Toubert et al., Paris, France, previously published that primary hypothyroidism and Graves' disease may occur in patients undergoing bone marrow transplantation after total body irradiation. They now show that bone marrow transplantation preceded by cytostatic drug treatment + anti-thymocyte globulin induces in 9/77 patients primary hypothyroidism, while of the available patients 12 months after transplantation, primary hypothyroidism was present in 12/35 patients. They conclude that in primary hypothyroidism, that occurs in these patients, other factors besides radiotherapy may induce this condition. |
