Is a more active attitude warranted in patients with subclinical thyrotoxicosis?

In 1985 one of the new sensitive thyroid stimulating hormone (TSH) assays was introduced as part of our laboratory routine for thyroid function testing. Consequently, we now routinely identify a small but not insignificant group of patients with 'subclinical thyrotoxicosis', i.e. a low serum TSH in conjunction with a normal serum free T4. We here present the results of a 2-year follow-up investigation, which includes 40 patients with subclinical thyrotoxicosis and 40 euthyroid control patients. The group with subclinical thyrotoxicosis was characterized by a mean age of 65 years and a high prevalence of nodular goitre. Twelve (30%) of the patients but none of the individuals in the control group were treated during the follow-up period because of clinical thyroid disease. Atrial fibrillation was found in 11 (28%) patients compared to four (10%) of the controls. Therapy should be considered more often than previously in patients with nodular goitre and subclinical thyrotoxicosis, particularly in conjunction with atrial fibrillation.