Iodine-sufficient areas

Thyroid autonomy appears as a solitary toxic nodule or toxic multinodular goitre. In toxic thyroid, the nodule s synthesis and secretion of thyroid hormones is autonomous from the thyroid-stimulating hormone (TSH), which is produced in the pituitary gland. Accordingly TSH is suppressed and the extranodular thyroid tissue is functionally downregulated. Thyroid autonomy occurs frequently in iodine-deficient countries, whereas it is much less common in iodine-sufficient areas. Constitu-tively activating mutations in the TSH receptor and in the Gs a protein are the major molecular aetiology of toxic thyroid nodules. 

Fenzi studied the prevalence of thyroid antibodies in a moderate endemic goiter area of Italy (Fenzi et ai, 1986). Schoolchildren n = 142) and their parents n = 159) were included. The overall frequency of Mic-Ab and Tg-Ab in the adult population was 14.4%, which was significantly higher than that in the sex- and age-matched control group living in an iodine-sufficient area. It was observed that antibodies were more common in subjects with goiter compared to subjects without goiter. 

A number of studies on the epidemiology of thyroid autoantibodies have been performed as descriptive studies in iodine-deficient areas. Results from some population-based studies from both iodine-deficient and iodine-sufficient areas are shown in Table 60.1. The results are ambiguous. 

The study group included 16 children born to 16 healthy mothers living in the moderately iodine deficient area (ID area), and 11 age-matched control children bom to 11 women from a marginally iodine-sufficient area (IS area). The characteristics of both areas when the children were conceived (1990-1992), and at the time of the study, are reported in Table 68.2. 

A high prevalence (68.7%) of ADHD is reported here in children Hving in a mild-to-moderate ID areas. ID-related ADHD affects intelligence. Indeed, the total IQ score of ADHD children was 22 points lower compared to control children from an iodine-sufficient area. 

Pregnant Women with Iodine Deficiency in Iodine-Sufficient Areas How Common is Hypothyroxinemia in Pregnant Women in Developed Countries ... 

The occurrence of ID in pregnant women in iodine-sufficient areas is not uncommon, because a high frequency of pregnancy-related iodine insufficiencies are reported from western European populations where schoolchildren showed normal or sufficient iodine intake (Delange, 2004 Garcla-Mayor et al, 1999 Rodriguez et al., 2002 Travers et al., 2006). For this reason information on the population s iodine intake obtained from studies in children may not be valid for adult populations, especially pregnant women or women of fertile age. 

Notes-. In an ISA anaplastic thyroid cancer is rare and the main type of differentiated thyroid cancer is papillary thyroid cancer. The ratio between papillary and follicular thyroid cancer changed due to the introduction of salf iodization. Abbreviations-. IDA, iodine deficient area rIDA, relative iodine-deficient area ISA, iodine-sufficient area DTC, differentiated thyroid cancer pap, papillary foil, follicular. 

The relative prevalence of the two forms of AIT depends on the amount of iodine intake. In iodine-sufficient areas such as Japan, with low incidences of toxic nodular goiter, only AIT II is observed. To distinguish between the two types of AIT, color-fiow Doppler sonography may be helpful, because of the higher vascularization in type I. 

It was demonstrated that thyroid autonomy due to toxic multinodular goiter accounts for up to 60% of all cases of thyrotoxicosis in iodine deficiency. In contrast, thyroid autonomy is rare in iodine-sufficient areas (3—10% of all cases of thyrotoxicosis) (Krohn et al., 2005 Laurberg etal., 1991, 1998). 

The fetus and neonate are both at risk of developing iodine-induced hypothyroidism (Table 96.3). Many cases of such hypothyroidism in fetuses and neonates have been reported, especially in iodine-deficient regions of Europe, but also in iodine-sufficient areas. Iodide goiter in neonates is usually a transient problem. However, tracheal obstruction due to such goiter can be fatal (Markou et al, 2001 Wolff, 1969). Transient hypothyroidism without elevation of thyroid-stimulating hormone (TSH) in extremely... 

Note The fetus and neonate are both at risk of developing iodine-induced hypothyroidism. Many cases of hypothyroidism in newborns have been reported, especially in iodine-deficient regions of Europe, but also in iodine-sufficient areas. 

The estimated incidence of amiodarone-induced thyroid dysfunction varies widely from 2 to 24% (Albert et ai, 1987). Amiodarone-induced hypothyroidism (AIH) is prevalent in iodine-sufficient areas, while AIT occurs... 

The main etiology of hypothyroidism in middle age and in the elderly in iodine-sufficient areas is autoimmune thyroid... 

Twenty two cerebral cortices from areas known to be iodine deficient were subjected to similar analysis. The results indicated that 5 and 5 monodeiodinase activities and T3 content show different pattern as compared to iodine sufficient area. It appears that in iodine deficient cortices T3 levels are maintained at adequate levels for neural development during the 14th to the 20th week of gestation. 

Difference of prevalence of thyroid disease in Japan from those in the other iodine-sufficient areas is not yet confirmed. However, it appears that prevalence of goiter is lower and that of hypothyroidism is higher in Japan than the others. 

N.Konno, K.Yuki, H. Taguchi, K. Miura, S. Taguchi, K. Ha giwara and S. Murakami. Screening for thyroid diseases in an iodine sufficient area with sensitive thyrotropin assays, and serum thyroid autoantibodies, and urinary iodide determinations. Clin. Endocrinol, (submitted)... 

Similar studies were carried out in schoolchildren and adults in Catania, as a control iodine sufficient area. 

Table. Iodine content of food from an iodine sufficient area (A) compared with Turkey (B)... 

The iodine content of drinking water varies widely in the country, sometimes even within the same county. It is generally low, less than 10 ig l/l for 50 % and 11-25 l/l for 30 % of Hungarian population. Eggs and milk from iodine deficient areas are also low in iodine content, 25 lg/kg, 28 ig/l respectively, but much higher, 100 ig/kg, 40 iig/l respectively, in iodine sufficient areas. 

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