Goiter size and thyroid function in an endemic goiter area in Northern Italy

Thyroid function was studied in a large number of subjects residing in Varsi, a town in the province of Parma, Italy. In this area, endemic goiter associated with moderate iodine deficiency [59 ± 3 (±SE) μg iodine/g creatinine], as defined by WHO criteria, affects 65% of the population. Serum T₄, T₃, thyroglobulin (Tg), and TSH concentrations were measured by RIA in 1218 subjects. The TSH response to TRH was determined in 108 subjects selected randomly from the groups with different grades of goiter. No significant change in serum T₄ concentrations was found in subjects with different grades of goiter. Serum T₃ concentrations were higher in subjects with the larger goiters. Serum Tg concentration progressively increased, and serum TSH progressively decreased with increasing goiter size. The TSH response to TRH was diminished in subjects with larger goiters. The findings of decreasing serum TSH concentrations and blunted TSH responses to TRH as goiter size increased suggest the possiblity of autonomous thyroid function in the larger goiters in subjects residing in this area of moderate iodine deficiency.