Clinical value of the thyrotropin-releasing hormone stimulation test in predicting mild hypothyroid state in chronic thyroiditis.

In order to evaluate the clinical usefulness of the TRH stimulation test in predicting premyxedematous state in chronic thyroiditis, serum TSH response to the i. v. injection of TRH was determined in 58 patients with chronic thyroiditis proven by needle or open biopsy. TSH radioimmunoassay was done by a double antibody technique, and the degree and pattern of TSH response were assessed based on our criteria established by the results obtained from 9 normal controls. According to Woolner's classification, 35 cases were diagnosed as diffuse type. 19 cases as focal type and 4 cases as hyperplastic. The basal levels of TSH were above the normal range in 71.4% of diffuse thyroiditis, whereas 36.8% of the patients with focal thyroiditis had an abnormally high basal TSH level. Responses of serum TSH to TRH was exaggerated in 67.1% of all patients; 80.0% in diffuse type and 47.4% in focal type. Concerning TSH response curve, 15 patients were judged as "prolonged", and 8 patients as "delayed" response. No weak responder in the TRH test was found in patients with high basal TSH level, 91% of whom had an exaggerated response. Serum levels of thyroxine and triiodothyronine inversely correlated with basal, maximal TSH levels (p less than 0.01) and increment of TSH (delta TSH) after TRH injection (p less than 0.01). Thyroidal uptake of I131 also inversely correlated with basal TSH level (p less than 0.05) but not with maximal TSH and delta TSH. From the fact that an elevation of basal TSH level and its hyperresponsiveness to TRH administration develop in a much more exaggerated fashion compared to the changes in other parameters of thyroid function, it was concluded that TRH test provides a useful rationale for the early diagnosis of premyxedema in chronic thyroiditis.