PURPOSE: To develop a strategy to identify cases of endogenous subclinical hyperthyroidism and free triiodothyronine (free T3) thyrotoxicosis in otherwise healthy ambulatory patients. PATIENTS AND METHODS: In a retrospective study we reviewed the records of ambulatory patients who had thyroid stimulating hormone (TSH) levels determined between October 1, 1991 and August 31, 1992. Each patient also had a simultaneous free thyroxine (free T4) measurement. Patients were excluded from consideration if they had active, concurrent non-thyroidal illness, psychiatric disease, known hypothalamic/pituitary lesions, were under treatment for hyper- or hypothyroidism, were on drugs known to affect TSH levels, or were pregnant. Patients without exclusions were diagnosed with free T3 toxicosis if they had: (1) a markedly subnormal TSH level (less than or equal to 0.1 mU/L), (2) a normal free T4, (3) a normal total T3, (4) evidence of a primary thyroid abnormality (e.g., autonomous function on a thyroid scan), and (5) an elevated free T3 level by tracer equilibrium dialysis. Patients meeting conditions 1-4, but with normal free T3 levels, were considered to have subclinical hyperthyroidism. RESULTS: One thousand twenty-five patients had TSH and simultaneous free T4 determinations, and 148 of these had markedly subnormal TSH but normal free T4 levels. Three patients met the criteria for free T3 toxicosis and three had subclinical hyperthyroidism. All six patients had either multinodular glands or a single nodule on thyroid exam. Four patients were treated with radioactive iodine or surgery, resulting in reversal of the TSH suppression in three cases. CONCLUSION: Apparently healthy ambulatory patients with subnormal TSH levels should be worked up with measurements of free T4 and total T3. If these are normal, a T3 level (by tracer equilibrium dialysis) be obtained to distinguish subclinical hyperthyroidism from overt free T3 toxicosis. A thyroid scan and radioiodine uptake measurement can be obtained to substantiate the diagnosis. Some patients with these conditions will benefit from treatment.
PURPOSE: To develop a strategy to identify cases of endogenous subclinical hyperthyroidism and free triiodothyronine (free T3) thyrotoxicosis in otherwise healthy ambulatory patients. PATIENTS AND METHODS: In a retrospective study we reviewed the records of ambulatory patients who had thyroid stimulating hormone (TSH) levels determined between October 1, 1991 and August 31, 1992. Each patient also had a simultaneous free thyroxine (free T4) measurement. Patients were excluded from consideration if they had active, concurrent non-thyroidal illness, psychiatric disease, known hypothalamic/pituitary lesions, were under treatment for hyper- or hypothyroidism, were on drugs known to affect TSH levels, or were pregnant. Patients without exclusions were diagnosed with free T3toxicosis if they had: (1) a markedly subnormal TSH level (less than or equal to 0.1 mU/L), (2) a normal free T4, (3) a normal total T3, (4) evidence of a primary thyroid abnormality (e.g., autonomous function on a thyroid scan), and (5) an elevated free T3 level by tracer equilibrium dialysis. Patients meeting conditions 1-4, but with normal free T3 levels, were considered to have subclinical hyperthyroidism. RESULTS: One thousand twenty-five patients had TSH and simultaneous free T4 determinations, and 148 of these had markedly subnormal TSH but normal free T4 levels. Three patients met the criteria for free T3toxicosis and three had subclinical hyperthyroidism. All six patients had either multinodular glands or a single nodule on thyroid exam. Four patients were treated with radioactive iodine or surgery, resulting in reversal of the TSH suppression in three cases. CONCLUSION: Apparently healthy ambulatory patients with subnormal TSH levels should be worked up with measurements of free T4 and total T3. If these are normal, a T3 level (by tracer equilibrium dialysis) be obtained to distinguish subclinical hyperthyroidism from overt free T3toxicosis. A thyroid scan and radioiodine uptake measurement can be obtained to substantiate the diagnosis. Some patients with these conditions will benefit from treatment.
Authors: Avantika C Waring; Stephanie Harrison; Mary H Samuels; Kristine E Ensrud; Erin S LeBLanc; Andrew R Hoffman; Eric Orwoll; Howard A Fink; Elizabeth Barrett-Connor; Douglas C Bauer Journal: J Clin Endocrinol Metab Date: 2012-01-11 Impact factor: 5.958
Authors: Ali Abbara; Sophie A Clarke; Rosalind Brewster; Alexia Simonnard; Pei Chia Eng; Maria Phylactou; Deborah Papadopoulou; Chioma Izzi-Engbeaya; Amir H Sam; Florian Wernig; Eliza Jonauskyte; Alexander N Comninos; Karim Meeran; Tom W Kelsey; Waljit S Dhillo Journal: Front Endocrinol (Lausanne) Date: 2020-05-12 Impact factor: 5.555