Relevance of increased serum thyroxine concentrations associated with normal serum triiodothyronine values in hypothyroid patients receiving thyroxine: a case for "tissue thyrotoxicosis"

Fifteen patients receiving standard thyroxine replacement therapy (100-200 micrograms daily) for primary hypothyroidism and who had persistently raised free thyroxine concentrations in their serum were investigated to see whether the dose being given was too high. In addition to the usual thyroid ho...

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Bibliographic Details
Published in:BMJ 1984-12, Vol.289 (6459), p.1645-1647
Main Authors: Jennings, P E, O'Malley, B P, Griffin, K E, Northover, B, Rosenthal, F D
Format: Article
Language:English
Subjects:
Adult
Aged
Biological and medical sciences
Blood
Clinical Research
Dosage
Hormones
Hormones. Endocrine system
Humans
Hypothyroidism
Hypothyroidism - blood
Hypothyroidism - drug therapy
Hypothyroidism - physiopathology
Medical sciences
Middle Aged
Pharmacology
Pharmacology. Drug treatments
Systole
Thyroid hormones
Thyrotoxicosis
Thyroxine - administration & dosage
Thyroxine - blood
Thyroxine - therapeutic use
Triiodothyronine - blood
Triiodothyronine, Reverse - blood
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Summary:Fifteen patients receiving standard thyroxine replacement therapy (100-200 micrograms daily) for primary hypothyroidism and who had persistently raised free thyroxine concentrations in their serum were investigated to see whether the dose being given was too high. In addition to the usual thyroid hormone assays systolic time intervals (which indicate left ventricular contractility) were calculated as accurate reflectors of tissue thyroid activity. All patients showed the expected increased free and total thyroxine concentrations; but mean total and free concentrations of triiodothyronine were normal, while reverse triiodothyronine values were raised. Mean systolic time intervals were significantly reduced as compared with normal and fell within the thyrotoxic range. Seven patients subsequently had their doses of thyroxine reduced by 50 micrograms daily and were reinvestigated one month later. All showed significant falls in circulating thyroxine and triiodothyronine concentrations and an increase in mean systolic time intervals to the normal range. In patients receiving thyroxine replacement therapy for primary hypothyroidism a raised serum thyroxine concentration may indicate tissue thyrotoxicosis and should prompt a reduction of the thyroxine dose.
ISSN:0007-1447
0267-0623
0959-8138
1468-5833
DOI:10.1136/bmj.289.6459.1645