In most patients a low thytrotopin (TSH) level is accompanied by elevated or depressed thyroid hormone levels. The presence of a low serum TSH level with normal free T3 and free T4 hormone levels can be seen in a number of conditions.
Synonym: pseudohyperthyroidism
Situations with a low TSH but normal levels of thyroid hormones:
(1) advanced age
(2) subclinical hyperthyroidism (due to thyroiditis, etc)
(3) pituitary insufficiency with thyroid hormone replacement
(6) transiently after a severe, life-threatening illness (with or without dopamine infusion)
(7) after an episode of acute psychosis or severe depression
(8) glucocorticoid therapy
(9) statin therapy
where:
• HCG can stimulate the TSH receptor, so an elevated HCG can result in a reduced serum TSH. The serum TSH tends to return to normal in the second and third trimester of a pregnancy.
• In theory autoimmune thyroiditis together with autoimmune hypophysitis could cause the pattern.
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