DEVELOPMENT OF HYPERTHYROIDISM IN NODULAR GOITER AND THYROID MALIGNANCIES IN AN AREA OF RELATIVELY LOW IODINE INTAKE

A high incidence of toxic nodular goiter has recently been described i n areas of relatively low iodine intake. We studied the development of hyperthyroidism in nodular goiter and thyroid malignancies in an area of relatively low iodine intake (median 87 mu g/24 h). The material c omprised a total of 557 patients admitted to our department in the per iod 1978-88. The follow-up material consisted of 214 patients with a m edian age of 55 yr (19-86). Eighty-eight percent were females, The per iod of observation was 33 months (1-205). All patients had technetium thyroid scans, serum T3, serum T4, T3 uptake test and serum TSH perfor med, TRH tests were performed in 58 patients. During the follow-up per iod 45 initially euthyroid patients became hyperthyroid (18%). The inc idence increased with age, and the median age in the group, who develo ped hyperthyroidism, was 65 yr, An estimated minimal incidence of toxi c nodular goiter was 23/100,000/yr. Contrary to previous assumption, h yperthyroidism developed frequently in elderly patients with nodular g oiter in a low iodine intake area. Thyroid cancer was found in 13 pati ents corresponding an estimated incidence of 1.5/100,000/yr, The cance r incidence was very low compared to other nordic countries with high iodine intake. This finding may suggest a possible influence of iodine intake on the incidence of thyroid cancer.