Normal thyrotrophin response to intravenous thyrotrophin releasing hormone administration: the best index of optimal L-thyroxine therapy in primary hypothyroidism.
Normalization of basal thyrotrophin (TSH) level is used as the endpoint in L-thyroxine (L-T4) therapy of primary hypothyroidism. However, several reports have questioned the reliability of this index because of seasonal variation of TSH. Therefore, we studied 85 consecutive patients with primary hypothyroidism over a period of 3.5 y. In these patients, TSH response (delta TSH) to intravenous thyrotrophin releasing hormone (TRH) administration was examined when basal TSH was normalized with L-T4 therapy. Eight patients showed a blunted response (delta TSH less than 5 microU), whereas 27 patients demonstrated an exaggerated response (delta TSH greater than 25 microU). Thus, 42% of patients were apparently on inappropriate L-T4 dosage. These abnormal TSH responses normalized on adjusting the L-T4 dosage alone; prolonged therapy with the same dose failed to normalize TSH responses. Minor seasonal variations of basal TSH were observed in 30% of patients. However, TSH response to TRH remained normal. Hence, no adjustment of L-thyroxine dose was required. This study, therefore, demonstrates that normalization of TSH response to TRH administration rather than basal TSH may be the best index of adequate L-thyroxine therapy in primary hypothyroidism.
D000328:Adult; D000368:Aged; D005260:Female; D006801:Humans; D007037:Hypothyroidism / Q000097:blood / Q000188:drug therapy*; D008297:Male; D008875:Middle Aged; D013972:Thyrotropin / Q000097:blood*; D013973:Thyrotropin-Releasing Hormone / Q000494:pharmacology*; D013974:Thyroxine / Q000097:blood / Q000627:therapeutic use*; D014284:Triiodothyronine / Q000097:blood
D014284:Triiodothyronine; D013973:Thyrotropin-Releasing Hormone; D013972:Thyrotropin; D013974:Thyroxine