Iodine metabolism in patients with Hashimoto´s
thyroiditis shows qua._titat~va avid gza:itative abno-, rmalities which may vary significartiy from patient to patient and which do not corre:ate well with the type of morphologic changes seen in the thyroid glands or with the clinical picture. These abnormalities in iodine metabolism were summarized by Buchanan and co-workers and can be conder.s:d ir_ta the following statements about the thyroid -grand. involved by Hashimoto´s thyroiditis: (1) it may show release of trapped iodine ("iodine escape"), (2) it has a diminished ability to maintain iodine stores, and (3) if the exchangeable iodine pool in the gland is small, it may have a high tarnover rate of exchangeable iodine. Nonhormo ai iodine secretion and increased stimulation Ly thyroidstimulating hormone (TSH) may be seen, and the thyroid gland is particularly sensitive to administered iodine in Hashimoto´s thyroiditis.
Some of the abnormalities which may exist in Hashimoto´s thyroiditis, such as increased TSH stimulation and decreased intrathyroidal iodine pool, have also been shown experimentally to influence the serum triiodothyronine (T3)/thyroxine (T4)ratio and to lead to an increase in serum T3.
The purpose of this study was to investigate whether significant abnormalities of concentrations of serum T3 T4 and TSH exist in patients with Hashimoto´s thyroiditis, whether measurements of this value in serum, would contribute to the understanding of abnormalities in iodine metabolism in Hashimoto´s thyroiditis or assist in its diagnosis and whether the thyroid radioactive iodine uptake (RAIU) and T3 RBC uptake tests reflect the functional state of the thyroid gland.
Serum levels of T3 T4 and. TSH, 24-h RAILS and T3 RBC uptake were examined in 32 cases (15 euthyroid, 12 hypothyroid, and 5 hyperthyroid) of 86 patients who were diagnosed of Hashimoto´s thyroiditis at Severance Hospital during the period from 1965 to 1977.
The following results were obtained:
1. The ratio of male to female was 1:85. The age distribution was dispersed between 10 and 62 years
of age and over half of the cases were in 4th (31.4%) and 3rd (24.4%) decade.
2. In the euthyroid patients :with, Hashimoto´s dieease (15.cases;.46.9%),"serum T3 concentration was, 95 260ng/100ml (mean, 183 3ngl100m1), T4 concentration 4.8-15.6μg/100.m1 (mean, 8.3 μg/100m1) and the T3/T4 ratio 0.009´ 0.054(mean, 0.025). The 24-h RAIU showed only 4 cases (28.6%) in normal range (1545%), 1 case (21%) in decreased state and 9 cases (64.3%) in increased state. The T3-RBC uptake test revealed 8 cases (61.5%) in normal range (11.19%), 1 case (7.7%) in decreased state and 4 cases (30.8%) in increased state.
3. In the hypothyroid patients with Hashimoto´s disease (12 cases; 37.5%), serum T, concentration was 100-275ng/100m1 (mean, 170.5ng/100ml) and T4 concentration 1.6 5.5Lg/100ml (mean, 3.5μg/100ml). The T3/T4 ratio was 0.026^-0.108 (mean, 0.051) which varied widely, and the mean value of the ratio was twice higher than that of any of the other groups. Serum TSH ranged from 13.5 to 316μU/ml (mean, 106. 1μU/ ml) which was markedly higher than in any of the other groups (Prl. In the hyperthyroid patients with Hashimoto´s disease (5 cases; 15.6%),serum T3 concentration with 225. 494μg/100m1 (mean, 373.4μg/lfl0ml) and T4 concentration with 7.2-24.5μg/100ml (mean,. 17.4μg/100m1) were markedly higher than in any of the other groups. The T3/T4 ratio ranged from 0. 011 to 0. 053 (mean, 0.026), which was similar to euthyroid group. The RAIU showed 4 cases (80%) in increased state and i case (20%) in normal range. The T3-RBC uptake test revealed 4 cases (80%) in increased state and 1 case (20%) in normal range.
In a brief of this study, there was-no specific abnormality in the thyroid function tests in Hashimoto´s disease because the functional state of the
thyroid gland was variable; However, in the hypothyroid patients with the disease, the T3/T4 ratio was significantly higher than in any of the other groups- as the result of decreased serum T4 and increased serum- T3 concentrations. At the same time, serum TSH concentration was markedly increased. It is also observed that the RAIU and T3 RBC uptake tests seemed to be inadequate in the diagnosis of Hashimoto´s disease.
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