Iceland hyperthyroidism

Over the years, people living with iodine deficiency tend to develop multifocal thyroid autonomy, and multinodular toxic goiter is a common cause of hyperthyroidism. The difference in relative distribution of the four most common causes of hyperthyroidism in Iceland, with high iodine intake, and Judand, Denmark, with mild-to-moderate iodine deficiency, is shown in Figure 47.3. In Iceland, Graves ... 

Figure 47.3 Nosological types of hyperthyroidism with different iodine intake levels. Relative frequency of the four most common nosological types of hyperthyroidism in Iceland, with relatively high iodine intake from consumption of fish and high iodine content of dairy products, and from East Jutland, Denmark, with mild-to-moderate iodine deficiency. MNTG, multinodular toxic goiter GD, Graves disease STA, solitary toxic thyroid adenoma SAT, subacute thyroiditis. Data from Laurberg et al., (1991).

In a population-based study of 68-year-old people living in Iceland and in Jutland, subclinical hypothyroidism was much more prevalent in Iceland, with sufficient to excessive iodine intake, than in an area of Jutland, with moderate iodine deficiency (Figure 47.4) (Laurberg et al., 1998). Subclinical hyperthyroidism was much more common in Jutland, as discussed above (Figure 47.4). 

In contrast to Jutland, the incidence of diagnosed hyperthyroidism in Iceland was very low, but subclinical hypothyroidism was very common. The incidence of all causes of hyperthyroidism was lower in Iceland than in Judand (about 2 5 per 100 000 per year vs. 40 per 100000 per year). 

Fig. 1. Relative contribution of different types of thyroid disease to the incidence of hyperthyroidism in East-Jutland, Denmark, and in Iceland. Onfy the contr ution of the four major forms is shown. GD = Graves disease, MNG = multinodular toxic goitre, STA = solitary toxic adenoma, SAT = subacute and painless thyroiditis. The numbers represent the percentage of all cases.

The incidence of all types of hyperthyroidism was higher in East-Jutland (38.7/100,000/year) than in Iceland (23.6/100,OOO/year) with some striking differences in the contribution of different Tpes of hyperthyroidism to the disease (fig 1). While Graves disease was the dominating cause of hyperthyroidism in Iceland, the most common cause of hyperthyroidism in East-Jutland was multinodular toxic goitre. 

Fig. 2. The age-specific incidences of all forms of hyperthyroidism in East-Jutland and in Iceland. P<0.01, P<0.001.

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