[Metabolic evaluation and etiology of "preclinical hypothyroidism": a preliminary report].

The TRH test, using synthetic TRH (TSH-releasing hormone) is the most sensitive test for the assessment of thyroid function. It may show elevated basal TSH and/or an exaggerated TSH response to TRH, despite normal thyroid hormone levels (T4, FT4I, T3). This condition is termed "preclinical hypothyroidism" (pc hypo). Thyroid hormone levels, the clinical index of Billewicz and metabolic impact on target tissues were studied prospectively in 38 pc hypo women and compared with 20 controls matched for age, weight and sex and 9 patients with overt hypothyroidism. For metabolic evaluation at the tissue site two new metabolic tests were developed and standardized, the systolic time intervals (STI) and sex-hormone-binding globulin (SHBG), which were used in conjunction with the ankle reflex time (ART) and lipids (cholesterol and triglycerides). The thyroid hormones T4, FT4I and T3 in pc hypo (77.8 +/- 2.0 nmol/l; 71.8 +/- 2.3; 1.92 +/- 0.07 nmol/l respectively; mean +/- SEM) were within the normal range (by definition), but significantly lower in comparison with the normal controls (105.5 +/- 3.3 nmol/l; 97.8 +/- 3.1; 2.91 +/- 0.12 nmol/l respectively; p less than 0.001). The clinical index and metabolic parameters SHBG and ART showed significant hypothyroid changes. STI (measured as preejection period) and lipids were not yet significantly different from the controls despite a hypothyroid tendency in many single individuals. The etiology in 144 patients with pc hypo (out of 2969 TRH tests) was analysed and the following causes identified: a) treated hyperthyroidism (38 after radioiodine, 5 after partial thyroidectomy, 5 after antithyroid drugs, 5 after radioiodine and partial thyroidectomy); b) simple goiter (7 without and 21 after partial thyroidectomy); c) autoimmune thyroiditis (27); d) other causes such as subacute thyroiditis (10); Riedel's thyroiditis (2), dyshormogenesis (2), drugs (6), treated toxic adenomas (2); e) etiology unknown or not identified (14).