»ENDEMIC COAST GOITRE« IN HOKKAIDO, JAPAN

Abstract

ABSTRACT A survey of goitre was made in the goitrous regions on the coast of Hokkaido, the northern island of Japan. Prevalence of goitre was confirmed in Hidaka coast and Rishiri Island. All goitrous patients were clinically euthyroid. The usual diet of the inhabitants of these districts consisted of a large quantity of iodine-rich seaweeds. Urinary excretion of iodine in five patients exceeded 20 mg per day. Studies of 131 I and 127 I metabolism were performed both during ingestion and after restriction of seaweed. When the patients were taking their usual diet, the mean thyroidal 131 I uptake in 57 patients was 9.6% at 3 hours and 11.7% at 24 hours. In five of seven patients plasma inorganic iodine and thyroidal iodine space were markedly increased. Significant discharge of thyroidal 131 I followed administration of thiocyanate. After withdrawal of seaweed from their usual diet, the plasma inorganic iodine was below 2 μg/100 ml but the thyroidal stable iodine uptake was higher than normal, depending on increase in thyroidal 131 I clearance rate. No discharge was shown by thiocyanate block. Plasma PBI and thyronine-iodine level and serum T 3 resin uptake were within the normal range. Radiochromatography of the thyroid tissue of the goitrous patients showed an increase in MIT/DIT ratio and a decrease in T 3 + T 4 proportion. No evidence for peripheral defect in DIT- 131 I deiodination was obtained. In a few patients restriction of seaweed induced a marked decrease in the size of goitre. The major cause of the endemic coast goitre seems to be excessive and longstanding intake of iodine from seaweed, and the similarities of iodine metabolism between the endemic coast goitre and iodide goitre arc discussed.