TSH-regulation and goitrogenesis in severe iodine deficiency

Since goitre prevalence increases sharply during the first two decades of life, age-related changes in the adaptation of the thyroid to iodine deficiency may occur. In order to study this, we have measured serum levels of TSH, T4 and T3 in 247 subjects (age range 5 to 60 years) living in an endemic goitre area of North Algeria (group A) and in 64 control subjects living in the non-iodine deficient city of Algiers (group B). TRH tests were also performed in 88 subjects from the goitrous area and in 30 controls. Patients from group A had significantly higher serum TSH and T3 and lower serum T4 than those from group B. Analysis of group A by age groups revealed significantly higher TSH concentrations in the 2-9 years group and a moderate but significant decrease in the group from 50-59 years. No significant changes were demonstrated for T4 and T3. In the goitrous area, the response of TSH to TRH was exaggerated and prolonged. delta TSH20 was inversely correlated with age. The different age groups showed a significantly progressive and continuous decrease of delta TSH20, delta TSH60, delta TSH120 from age 10-19 to age 50-59 years. Our findings thus show a sharp increase of TSH during the first decades of life, which coincides with the phase of maximal growth of the thyroid gland. These results suggest that TSH plays a definite role in the genesis of endemic goitre. The subsequent progressive decrease of TSH secretion and reserve, with unchanged T4 and T3, imply a gradual development of autonomous activity in longstanding multinodular goitre.