Raising free T4 targets to the upper tertile of normal in patients with central hypothyroidism led to a decrease in body mass index, waist circumference, and other metabolic and clinical issues in patients with central hypothyroidism, shows a new study.
Central hypothyroidism occurs as a result of a poorly functioning thyroid stimulating hormone (TSH) that only reaches low to normal levels. Low levels of TSH, along with low levels of free T4, usually suggests a diagnosis of central hypothyroidism—a condition that affects approximately 1 in 80,000 to 120,000 people. The first line of treatment for central hypothyroidism is thyroid hormone replacement therapy with the synthetic T4 hormone, levothyroxine. The goal is to achieve a free T4 target level in the upper tertile of normal.
In this study, which was presented by Hay Man So, MRCP, of Hong Kong at ENDO 2021 in March, researchers successfully raised free T4 target levels to the upper tertile of normal without triggering a significant increase in adverse effects over 48 weeks.
This was a single center, prospective open-label crossover trial of 51 patients (mean age 56±12.9 years, 27 male) with hypopituitarism and multiple hormonal deficiencies, such as central hypothyroidism. The patients were prescribed levothyroxine (L-T4) at different doses in order to achieve specific targets of lower, middle and upper free T4 and maintain those levels for 24 weeks. The patients were assessed for physiological changes, plus improvements in metabolic and peripheral tissue markers and cognitive and quality of life assessments. Dosages were adjusted as needed for a second 24-week testing period.
There were significant improvements in metabolic-related symptoms. Body mass index dropped from an average of 27.1±6.0 to 25.7±5.6 kg/m2, P<0.01); waist circumference dropped from (89.5±12.7 to 86.4±12.1 cm, P<0.01); diastolic blood pressure dropped from 79.1±12.9 to 74.5±12.9 mmHg, P<0.05; and, low density lipoprotein cholesterol dropped from 3.94±0.88 to 2.90±0.71 mmol/L, p<0.01). There was also significant increases in sex hormone binding globulin, increased ferritin and reduced creatinine kinase.
The presence of metabolic syndrome itself lessened as well with a drop to 29.0% from 48.2% (P <0.05). In these cases, there was no significant effect on heart rate, glycemic indexes, dementia prevalence and quality of life measures.
Ka Fai Lee, FRCP, Hay Man So, MRCP, Wai Han Mak, MRCP. “P51-9 – Evaluation of the Optimal Thyroxine Levels for Thyroxine Hormone Replacement in Patients With Central Hypothyroidism,” ENDO 2021. March 20, 2021.