Thyrotropin secretion in mild and severe primary hypothyroidism is distinguished by amplified burst mass and Basal secretion with increased spikiness and approximate entropy.
BACKGROUND
Twenty-four-hour TSH secretion profiles in primary hypothyroidism have been analyzed with methods no longer in use. The insights afforded by earlier methods are limited.


OBJECTIVE
We studied TSH secretion in patients with primary hypothyroidism (eight patients with severe and eight patients with mild hypothyroidism) with up-to-date analytical tools and compared the results with outcomes in 38 healthy controls.


METHODS
Patients and controls underwent a 24-h study with 10-min blood sampling. TSH data were analyzed with a newly developed automated deconvolution program, approximate entropy, spikiness assessment, and cosinor regression.


RESULTS
Both basal and pulsatile TSH secretion rates were increased in hypothyroid patients, the latter by increased burst mass with unchanged frequency. Secretory regularity (approximate entropy) was diminished, and spikiness was increased only in patients with severe hypothyroidism. A diurnal TSH rhythm was present in all but two patients, although with an earlier acrophase in severe hypothyroidism. The estimated slow component of the TSH half-life was shortened in all patients.


CONCLUSIONS
Increased TSH concentrations in hypothyroidism are mediated by amplification of basal secretion and burst size. Secretory abnormalities quantitated by approximate entropy and spikiness were only present in patients with severe disease and thus are possibly related to the increased thyrotrope cell mass.
Roelfsema
Ferdinand
F
Leiden University Medical Center, Department of Endocrinology and Metabolic Diseases, P.O. Box 9600, 2300 RC Leiden, The Netherlands. f.roelfsema@lumc.nl
Pereira
Alberto M
AM
Adriaanse
Ria
R
Endert
Erik
E
Fliers
Eric
E
Romijn
Johannes A
JA
Veldhuis
Johannes D
JD
D000328:Adult; D000368:Aged; D002940:Circadian Rhythm; D019277:Entropy; D005260:Female; D006801:Humans; D007037:Hypothyroidism / Q000378:metabolism*; D008297:Male; D008875:Middle Aged; D013963:Thyroid Hormones / Q000097:blood; D013972:Thyrotropin / Q000097:blood / Q000378:metabolism*; D055815:Young Adult
D013963:Thyroid Hormones; D013972:Thyrotropin