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Multinodular goitre and subclinical hyperthyroidism |
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As demonstrated in fig. 5, hyperthyroidism due to multinodular goitre is preceeded by a long period where the patient will have serum T4 and T3 in the normal range, but lower than normal serum TSH.
From the data in fig. 6 it would be anticipated that low serum TSH with subclinical hyperthyroidism would be more prevalent among elderly subjects in Jutland than in Iceland.
This pattern was demonstrated in a comparative study of cohorts of 68 years old subjects (fig. 7). Subclinical and even frank biochemical but undiagnosed hyperthyroidism was very common among the elderly from the low iodine intake area.
Figure 7a:
Figure 7b:
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Prevalence rates of various degrees of hyperthyroidism (with low serum TSH) (A) and hypothyroidism (with high TSH) (B) in Jutland and Iceland. Data from 7. |
The majority of these subjects had no clinical goitre. However, when examined by ultrasound thyroid enlargement was common among the elderly in Jutland (fig. 8). This figure in addition demonstrates the importance of other goitrogenic factors in populations with low iodine intake. In this case it is tobacco smoking with generation of thiocyanate, which inhibits both the NaI symporter and thyroid peroxidase.
Figure 8:
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Thyroid volume by ultrasound in 95 randomly selected 68 years old subjects from Jutland. None had been judged to have clinical goitre. Males: closed circles, females: open circles. Thyroid volume was significantly higher in smokers. A thyroid > 25 ml in males and > 18 ml in females was considered enlarged. Data from 7 . |
A frequent occurence of goitre and hyperthyroidism in elderly subjects is the most important clinical consequence of mild iodine deficiency. A high iodine intake as in Iceland is however associated with a higher prevalence of hypothyroidism (fig. 7).
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