Patterns of Recovery of the Hypothalamic-Pituitary-Thyroid Axis in Patients Taken off Chronic Thyroid Therapy

Abstract

To determine the patterns of recovery of the hypothalamic-pituitary-thyroid axis following long-term thyroid hormone therapy, TRH tests were performed on 8 euthyroid nongoitrous patients, 5 euthyroid goitrous patients, and 5 hypothyroid patients while they were taking full doses of thyroid hormone and 3, 7, 10, 14, 17, 21, 28, 35, 42, 49, and 56 days after stopping it. Serum TSH, T3, and T4 were measured before and at multiple intervals over a 4-h period after giving 500 mug TRH iv. In euthyroid non-goitrous patients, the mean duration of suppressed TSH response to TRH (maximum deltaTSH less than 8 muU/ml) was 12 +/- 4 (SE) days after stopping thyroid hormone and the mean time to recovery of normal TSH response to TRH (maximum deltaTSH greater than 8 muU/ml) was 16 +/- 5 days. None of the euthyroid nongoitrous patients ever hyperresponded to TRH; their average maximal deltaTSH was 24.5 +/- 2.2 muU/ml. Serum T4 fell below normal in 4 euthyroid non-goitrous patients, reaching lowest values at 4 to 28 days. While serum T4 was low, deltaTSH was subnormal. Normal increments of T4 and T3 after TRH occurred at 19 +/- 5 and 22 +/- 6 days, respectively. In the 5 goitrous patients, patterns of recovery of pituitary and thyroid function assessed by the same parameters were much less consistent. In the 5 hypothyroid patients, the mean duration of suppressed basal TSH and suppressed deltaTSH was 13 +/- 3 days; mean time to attain a supranormal basal TSH (greater than 8 muU/ml) was 16 +/- 4 days and to reach a supranormal deltaTSH (greater than 38 muU/ml) after TRH was 29 +/- 8 days. Following prolonged thyroid therapy in euthyroid patients, recovery of normal TSH responsiveness to TRH preceded recovery of the normal T3 and T4 response to TRH by 3 to 6 days. Basal serum TSH may be used to differentiate euthyroid from hypothyroid patients 35 days after withdrawal of thyroid therapy; the response to TRH does not improve this differentiation.

Peripheral Serum Thyroxine, Triiodothyronine and Reverse Triiodothyronine Kinetics in the Low Thyroxine State of Acute Nonthyroidal Illnesses

“…The study population consisted of 16 (11,12), dilantin (13), or heparin (14,15) were excluded as were patients with known or suspected hypothalamic or pituitary disease, head trauma (16), thyroid disease, or recent thyroid (17) or glucocorticoid hormone therapies (18,19 Table II.…”

Peripheral tissue mechanism for maintenance of serum triiodothyronine values in a thyroxine-deficient state in man.

“…The results of this study support the possible existence in euthyroid man of a peripheral tissue autoregulatory mechanism for maintaining serum T3 values in states of T4 deficiency. Whether this process Introduction It is axiomatic that thyroid stimulating hormone (TSH)' secretion plays a critical role in regulating thyroid gland function and, in turn, circulating thyroid hormone levels (1)(2)(3)(4)(5). For example, elevations in serum TSH induced preferential thyroidal triiodothyronine (T3) formation and secretion tend to maintain serum T3 values as circulating thyroxine (T4) levels fall as a result of either thyroid disease or iodine deficiency (2).…”

Hipotiroidismo congênito transitório: perfil das crianças identificadas no programa estadual de triagem neonatal de Minas Gerais, Brasil

“…Este critério baseou-se no trabalho de Krugman e cols. (12), que avaliaram a recuperação do eixo hipotálamo-hipófise-tiróide após terapia prolongada com hormônio tiroidiano em indivíduos com e sem hipotiroidismo. Esses autores concluíram que o TSH sérico basal pode ser usado para diferenciar pacientes eutiroidianos daqueles com hipotiroidismo 35 dias depois da suspensão da terapia com L-tiroxina, e que o teste de estímulo com TRH é dispensável para essa diferenciação.…”