Thyrotropin-axis adaptation in aging and chronic disease

The forgotten effects of thyrotropin-releasing hormone: Metabolic functions and medical applications

Thyrotropin-releasing hormone (TRH) causes a variety of thyroidal and non-thyroidal effects, the best known being the feedback regulation of thyroid hormone levels. This was employed in the TRH stimulation test, which is currently little used. The role of TRH as a cancer biomarker is minor, but exaggerated responses to TSH and prolactin levels in breast cancer led to the hypothesis of a potential role for TRH in the pathogenesis of this disease. TRH is a rapidly degraded peptide with multiple targets, limiting its suitability as a biomarker and drug candidate. Although some studies reported efficacy in neural diseases (depression, spinal cord injury, amyotrophic lateral sclerosis, etc.), therapeutic use of TRH is presently restricted to spinocerebellar degenerative disease. Regulation of TRH production in the hypothalamus, patterns of expression of TRH and its receptor in the body, its role in energy metabolism and in prolactin secretion are addressed in this review.

TSH reference range in older adults: a Brazilian study

Objective: To establish serum TSH reference values for a population of Brazilian elderly, and to compare them to those found in the adult population. Subjects and methods: Healthy volunteers aged 70 to 85 years, without known thyroid disease or risk factors for thyroid dysfunction, who did not use any medication that could potentially interfere with TSH, were selected. Subjects with goiter, palpable thyroid nodules, anti-thyroperoxidase antibodies, or altered free T4 were excluded. The sample consisted of 360 older adults (180 per sex). Results: TSH values corresponding to the 2.5th and 97.5th percentile of the sample were 0.2 and 4.62 mIU/L, respectively. TSH > 2.5 mIU/L was seen in 25.26% of the volunteers, > 3 mIU/L in 15.26%, and > 4 mIU/L in 6.1% of them. TSH values were slightly higher than those previously reported for adults (18-60 years). Conclusion: This study suggests an upper limit for normal TSH of approximately 4.6 mIU/L for the Brazilian elderly population.

Alterations in thyroid function tests in aged hospitalized patients: prevalence, aetiology and clinical outcome

BACKGROUND

Thyroid dysfunction is common in aged people and has recently been associated to mortality.

AIMS

Our aims have been (1) to assess the prevalence of alterations in thyroid function tests in hospitalized patients over age 60 years and (2) to study the relationship between thyroid functional status and mortality during hospitalization.

METHODS

We studied a group of 447 patients (62% women), aged 61-101 year, hospitalized during 2005. Thyroid dysfunction was assessed by measuring serum concentrations of thyrotrophin (TSH), free thyroxine (FT4), and free thriiodothyronine (FT3). Thyroid autoimmune status was evaluated through thyroid peroxidase (TPO) and thyroglobulin (TG) antibodies quantification.

RESULTS

Twenty-one patients (4.7%, 19 women) showed previously known thyroid dysfunction. 332 patients (74.3%) showed alterations in thyroid function tests. Euthyroid sick syndrome (ESS) was the derangement more frequently found (n = 278, 62.2%). After excluding ESS patients, 60 patients (13.4%) showed thyroid dysfunction: overt hypothyroidism, 14 (3.1%); subclinical hypothyroidism, 25 (5.6%); overt hyperthyroidism, 11 (2.5%), and subclinical hyperthyroidism, 10 patients (2.2%). Thyroid autoimmunity was positive in only 4.0% and 2.3% of patients, for TPOAb and TgAb, respectively. The presence of alterations in thyroid function tests was positively associated with the age of the patients and mortality during hospital stay (P < 0.001). Serum levels of FT3 were negatively related to death during hospitalization (OR 0.56; CI 95%, 0.38-0.81; P < 0.01).

CONCLUSIONS

About three quarters of patients admitted in our geriatric unit exhibited alterations in thyroid function tests. This finding was associated with elevated age and poor prognosis. The reduction of FT3 values was a powerful predictor for mortality during hospitalization in elderly patients.