Endemic Goiter in the Cauca Valley: II. Studies of Thyroid Pathophysiology1

Abstract

Prolonged supplementation with adequate or even high amounts of dietary iodine of 317 goitrous and 200 nongoitrous individuals from the endemic area of the Cauca Valley resulted in thyroidal ¹³¹I uptakes within the low normal range of values reported from nonendemic areas; serum PBI concentrations were similar to those accepted as normal; and urinary iodine excretions were above the levels observed in non-endemic areas. Normal renal clearances of iodine and high plasma inorganic iodide (PII) have also been found. The increments in thyroidal ¹³¹I uptakes and PB¹²⁷I concentrations after the administration of thyrotropin, normal values for PB¹³¹I and normal conversion ratios indicate that goitrous glands from the Cauca Valley are normally sensitive to tropic hormone, are not under maximal endogenous TSH stimulation, and therefore have an adequate functional reserve. Thus, it appears that intrathyroidal factors and not TSH activity account for the retardation in hormonal synthesis that has been encountered in the nodular component of nontoxic goiters. Parenchymatous nodular (PNG), colloid nodular (CNG) and mixed colloid-parenchymatous forms of goiter were found in 74 individuals of the present series. Except for nonsuppression by thyroxine that could certainly indicate parenchymatous nodules and scannings of the neck showing well-delineated “cold” areas which would suggest a PNG, none of the other physiological tests permitted us to differentiate among these 3 types of goiter. Since “cold” areas were encountered in noncarcinomatous patients with PNG, scanning of the neck appeared to be an unreliable test for the diagnosis of carcinoma of the thyroid gland.