The background of the study. Data concerning the frequency of both hyperthyroidism and hypothyroidism are rare. This study determined the numbers of existing and new cases in a large community from 1993 to 1997.
How the study was done. Subjects with hyperthyroidism or hypothyroidism living in Tayside, Scotland, were identified from a master patient index; a thyroid registry, databases containing prescription and radioiodine therapy data for the region; and mortality records. They were considered to have hyperthyroidism if they had been treated with an antithyroid drug, radioiodine, or surgery. Existing cases were those patients who had hyperthyroidism from January through June 1993, and new cases were those who were newly treated from July 1993 through April 1997. Subjects were considered to have hypothyroidism if they had received continuous thyroid hormone therapy. Existing cases of hypothyroidism were those treated from January through June 1993, and incident cases were those newly treated from July 1993 through October 1996.
The results of the study. In 1993 there were 1910 existing cases of hyperthyroidism, and from 1993 to 1997 there were 620 new cases. The midyear frequency of existing and new cases increased significantly, from 0.51 to 0.63 percent of the population. Among the 620 new cases, 526 (85 percent) were females and 94 (15 percent) were males. The overall new case rate from 1993 to 1997 was 0.46 per 1000 person-years. The overall rates (by decade of age) among adult women ranged from 0.78 to 1.29 per 1000 person-years and those for men from 0.06 to 0.45 per 1000 person-years.
For hypothyroidism, there were 5436 existing cases, and 3469 new cases. The midyear frequency increased from 2.18 to 2.98 percent. The new cases included 2969 females (86 percent) and 500 males (14 percent). The overall new case rate from 1993 to 1997 was 2.97 per 1000 person-years. Among adult women the overall incidence rates ranged from 1.83 to 9.72 per 1000 person-years and for men 0.24 to 4.85 per 1000 person-years.
The conclusions of the study. Among subjects living in a region of Scotland, the frequency of new cases of hyperthyroidism and hypothyroidism did not increase during the 1990s.
The original article. Flynn RW, MacDonald TM, Morris AD, Jung RT, Leese GP. The thyroid epidemiology, audit, and research study: thyroid dysfunction in the general population. J Clin Endocrinol Metab 2004;89:3879-84.