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ANALYSIS OF FACTORS IN HYPERTHYROIDISM, WHICH DETERMINE THE DURATION OF SUPPRESSIVE TREATMENT BEFORE RECOVERY OF THYROID STIMULATING HORMONE SECRETION
Author(s) -
FISCHER H. R. A.,
HACKENG W. H. L.,
SCHOPMAN W.,
SILBERBUSCH J.
Publication year - 1982
Publication title -
clinical endocrinology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.055
H-Index - 147
eISSN - 1365-2265
pISSN - 0300-0664
DOI - 10.1111/j.1365-2265.1982.tb03174.x
Subject(s) - endocrinology , medicine , thyroid , secretion , hormone , trh stimulation test , prospective cohort study , thyrotropin releasing hormone
SUMMARY In twenty‐three thyrotoxic patients a prospective study was undertaken to assess the time until restoration of TSH secretion. For several methodological reasons we chose to study a model in which the patients were deliberately continued on full dose treatment until biochemical hypothyroidism was established. The period until reappearance of TSH secretion varied between 42 and 293 days. In this time FTI had become subnormal, while T3 and the clinical index remained in the normal range. The interval until TSH restoration was not correlated with the parameters of thyroid status from the initial evaluation with the exception of a negative correlation with log PB 131 I 48 h ( r = 0·511; P < 0·02). The average follow up period in our patients was 115 days during which FTI decreased exponentially to 19±7 ± 20±5. The disappearance of T3 followed a biphasic course in which after 2–4 weeks T3 decline practically ceased and concentrations remained normal. Assuming that a FTI between 100 and 65 was the threshold value beneath which hypophyseal TSH synthesis and secretion could be expected, we were able to determine the interval between the corresponding date and the date of returning TSH secretion in twenty‐one patients. This latency time was 34 ± 9±7 days and proved completely independent of the total time until TSH reappearance. In contrast there was a highly significant correlation ( r = 0·987; P <0·001) between the time to reach the assumed threshold level and the time to recovery of TSH secretion. The disappearance of FTI, although widely variable from patient to patient, showed a constant rate throughout the full scale from elevated to practically absent concentrations. Thus, the initial part of the disappearance curve determines the length of time until restoration of TSH secretion. This is illustrated by the tight relationship ( r = 0·92; P < 0·001) between FTI after 28 days of treatment and the time when TSH started to rise. Knowledge of the FTI on day 28 allows treatment to be tailored to the needs of the individual patient.