The Treatment of Subclinical Hypothyroidism Is Seldom Necessary

Extract

Subclinical hypothyroidism (SH) is a common disorder with a prevalence ranging from 1–10% of the adult population in most community studies (1–14). The risk of developing SH increases with female gender, advanced age, and greater dietary iodine intake. The view that most subjects with SH should be treated with l-thyroxine has gained increasing credence (15–17). A limited number of placebo-controlled randomized trials involving a small number of patients with SH have been performed (18–22), and several of these studies show that l-thyroxine therapy may reduce symptoms of hypothyroidism (18, 22). Other studies in subjects with SH have shown that l-thyroxine lowers low-density lipoprotein (LDL) cholesterol, improves cardiac function, and diminishes neuropsychiatric symptoms (15–17). A recent cross-sectional observational study noted an association between SH and atherosclerotic disease (13). On initial assessment then, it appears that the position advocating l-thyroxine therapy for most subjects with SH enjoys strong experimental support.

However, careful scrutiny of the entire spectrum of primary data bearing on the question of whether or not SH should be treated with l-thyroxine yields a legitimate contrary view. There are as many placebo-controlled randomized trials that observed no reduction in symptoms of SH (20, 21) as there are that note benefits of treatment. Other reports have noted the doubtful clinical significance and frequent statistical nonsignificance of l-thyroxine therapy on changes in LDL cholesterol, myocardial performance, and neuropsychiatric parameters. No association between SH and ischemic heart disease was shown in the Whickham survey (23), the most extensive longitudinal study of thyroid disease ever conducted. Such conflicting findings stem from inconsistencies of the reports in the variable definition of SH, the wide degree of thyroid failure examined, as well as the heterogeneous age, gender, and ethnicity of the subjects tested.