To the Editor.
—Recently, frequency of silent thyroiditis (lymphocytic thyroidits with spontaneously resolving hyperthyroidism) has been much debated in the United States. Nikolai et al1 found the disorder in 10% to 20% of their cases of hyperthyroidism. However, in a recent report in the Archives, Vitug and Goldman2 reported that there was only one case that fulfilled the criteria for diagnosis in a three-year review of 86 patients with hyperthyroidism encountered in their hospital. They pointed out that most of the reported cases were from Japan and the areas around the Great Lakes, especially in Michigan, Minnesota, Wisconsin, and Ontario.We report on the incidence of silent thyroiditis among patients with hyperthyroidism in the Kumamoto area of Japan. Fifty-six patients with thyrotoxicosis were seen in our clinic from January 1984 to October 1985. From January 1984, radioactive iodine uptake was carried out for all patients with thyrotoxicosis. Among