Subclinical hyperthyroidism in patients with nodular goiter represents a hypermetabolic state.

The aim of the study was to examine the metabolic status in patients with suppressed TSH but values of FT4I and T3 within the reference range (subclinical hyperthyroidism [sH]). Thirteen patients and 13 control persons with nodular goiter were included. The metabolic state was determined by measurements of basal oxygen consumption (VO2), bone mineral density (BMD), and the circadian variation of TSH. Further was the pituitary thyroid axis examined by studying the effect of lowering thyroid hormones by methimazol treatment. The circadian variation of TSH varied from that of normal persons as the night surge was abolished. The basal VO2 was significantly higher and BMD was significantly lower in patients with sH compared to control persons. Restoration of TSH by lowering of thyroid hormone concentrations lead to a normalization of VO2 and restoration of the circadian variation of TSH. The preserved pituitary thyroid axis, the abolished circadian TSH variation, the increased VO2, and decreased BMD in patients with suppressed TSH, but peripheral thyroid hormone concentrations within the reference range, indicate a hyper metabolic state, which might reflect either an altered cellular set point or an increased sensitivity towards thyroid hormones in peripheral cells and in the thyrotrope cells.