Best Practice & Research Clinical Endocrinology & Metabolism
4Natural history, diagnosis and management of subclinical thyroid dysfunction
Introduction
Subclinical thyroid dysfunction (STD) is an early condition of mild thyroid hormone excess (subclinical hyperthyroidism) or deficiency (subclinical hypothyroidism), characterized by abnormal serum thyroid stimulating hormone (TSH) and normal free thyroxine (FT4) and free tri-iodothyronine (FT3).1, 2
The upper limit of the normal range has progressively decreased in the last decades from 10–7.0 mU/L to 4.0–5 mU/L, with the use of thyroid antibody tests.
Subclinical hypothyroidism (SHypo) is characterized by elevated serum TSH and thyroid hormone levels at the lower limit but within their respective reference range.1, 2, 3, 4 It is necessary to distinguish between patients with mildly increased serum TSH levels (5–9 mU/L) and patients with more severely increased serum TSH levels (≥10 mU/L) (Table 1). About 75% of all SHypo patients have mild disease.
The enhanced sensitivity of the TSH assay with the second and the third generation immunometric evaluation has helped differentiate the lower limit of the normal range from complete and incomplete TSH suppression.1, 2, 3
Subclinical Hyperthyroidism (SHyper) is defined as low-undetectable serum TSH and thyroid hormone (FT4 and FT3) concentrations in the upper limit but within their respective reference range.1, 2, 3, 4 Clinicians usually distinguish mild SHyper when the serum TSH level is low, but still detectable (0.1–0.4 mU/L), from a more severe condition in which TSH is undetectable and fully suppressed (Table 1).
Mild SHyper is the prevalent form of this dysfunction because it is present in about 75% of patients.2
The high frequency and the various implications of STD require the need to establish a correct diagnosis, clinical assessment and treatment of this disorder.4, 5
Section snippets
Prevalence and etiology
The prevalence of SHypo has been reported to be between 4 and 20% of the adult population samples.1, 2, 6 This wide range reflects some important differences among the populations studied in terms of race and dietary iodine intake, the dissimilar characteristics among the patients evaluated (age, gender, body mass index) and the different methods of TSH evaluation (TSH cut-off values used to define SHypo).1, 2, 7
Hashimoto thyroiditis, an autoimmune disorder of the thyroid gland is the most
Prevalence and etiology
The most common cause of exogenous SHyper (Exo SHyper) is an excessive L-T4 replacement therapy in hypothyroid patients or an intentional TSH suppression in patients with differentiated thyroid cancer (DTC).1, 2, 72 Exogenous SHyper is present in about 20–40% of patients receiving L-thyroxine (L-T4) therapy.9
Long-term L-T4 suppression of TSH is the traditional treatment for patients with DTC at high-risk of recurrence and progression.75, 76 Experimental and clinical data have demonstrated that
Disclosure summary
The author has nothing to disclose.
Acknowledgment
Alfonso Gruosso for writing English assistance.
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Subclinical hypothyroidism in older individuals
2022, The Lancet Diabetes and EndocrinologyCitation Excerpt :One potential reason to treat subclinical hypothyroidism is to prevent progression to overt hypothyroidism. The annual rate of progression to overt hypothyroidism is 4·3% in patients of all ages with both high concentrations of serum TSH and positive thyroid peroxidase (TPO) antibodies,20,21 2·8% in patients of all ages with normal concentrations of serum TSH and positive TPO antibodies,20 and 2–6% in patients of all ages after partial thyroidectomy.20 Several cross-sectional and longitudinal studies in healthy people with no evidence of thyroid disease have shown that TSH concentration progressively increased with age without an accompanying fall in free T4 concentration.22–24
Subclinical thyroid dysfunction and cardiovascular consequences: An alarming wake-up call?
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2020, Hormonal Signaling in Biology and Medicine: Comprehensive Modern EndocrinologyThyroid Hormones
2019, Hormonal Signaling in Biology and Medicine: Comprehensive Modern EndocrinologyThe Management of Thyroid Abnormalities in Chronic Heart Failure
2019, Heart Failure ClinicsCitation Excerpt :Moreover, SHypo can be a risk factor for cardiac death in patients with chronic HF.15 Treatment of overt hypothyroidism and SHypo with levothyroxine (LT4) is able to prevent the progressive left ventricle dysfunction and improve systolic and diastolic dysfunctions, SVR, and endothelial function, improve cardiac output thereby increasing (CO) and stroke volume.11,12,16 Therefore, LT4 in replacement doses is recommended by international guidelines and expert opinions in patients with serum TSH above 10 mU/L.2,3,17,18 This treatment also should be considered when serum TSH is persistently increased in mild disease (TSH 4.5–9.9 mU/L), especially in patients with a high CV background.2,3,17,18
The association of lymphocyte with hypothyroidism in obstructive sleep apnea
2024, BMC Pulmonary Medicine