What is subclinical hypothyroidism?
Subclinical hypothyroidism is a condition in which TSH values are high, but the levels of the thyroid hormones (T3 and T4) are still normal and, unlike true hypothyroidism (in which TSH levels are high and the thyroid hormone values are lower than normal), there are generally no symptoms.
It is a relatively common condition that affects approximately 5-10% of the adult population, predominantly occurs above the age of 55-60 and more frequently affects women.
What are the symptoms of subclinical hypothyroidism?
Patients with subclinical hypothyroidism generally either have no symptoms at all or experience mild symptoms that may include drowsiness, difficulties concentrating, brittle hair, anxiety, intolerance towards the cold or muscle weakness.
Subclinical hypothyroidism can also cause changes in the concentration of fats in the blood (especially increases in cholesterol levels) and in blood vessel function, which can lead to a higher risk of developing, for example, atherosclerosis, a disease in which the inside of an artery narrows due to a build-up of fatty deposits, or cardiovascular problems in general.
What are the causes of subclinical hypothyroidism?
There are several possible causes that can result in the onset of subclinical hypothyroidism, including an insufficient iodine intake, radiotherapy to the neck or head, certain medicines, and ageing, but the main cause is Hashimoto’s thyroiditis, in which the immune system gradually destroys the thyroid, which therefore over a period of time is no longer able to produce sufficient quantities of thyroid hormones.
What tests should be done?
In order to diagnose subclinical hypothyroidism, the doctor will prescribe a blood test to analyse TSH and thyroid hormone levels: patients with subclinical hypothyroidism will have TSH levels higher than the reference limit value (usually between 4.0 and 10.0 mIU/L) and thyroid hormone levels within the normal ranges.
Following a finding of high TSH values and normal thyroid hormone levels, the doctor may ask to repeat the TSH, fT4 fT3 and anti-thyroid peroxidase (Anti-TPO) antibody tests after 2-3 months. If subclinical hypothyroidism is confirmed, the patient will also be asked to have a thyroid ultrasound scan.
How is subclinical hypothyroidism treated?
Depending on the severity of the symptoms, the presence of risk factors, such as a history of thyroid disease, and the patient’s age and TSH values, the doctor will consider whether or not to prescribe pharmacological treatment.
In patients under 65-75 years of age with TSH values ≥10 mU/L therapy is always indicated, even in the absence of symptoms; if, on the other hand, the TSH value is between 4.5 and 9.9 mU/mL, treatment is only indicated in the presence of symptoms, cardiovascular disorders, for example heart failure, or hyperlipidaemia (increase in cholesterol and/or triglycerides in the blood).
In elderly individuals over 75 years of age, subclinical hypothyroidism is very common because TSH increases with age, regardless of the presence of an actual thyroid dysfunction. In these cases treatment is considered, preferably starting therapy at very low doses, if the high TSH values are accompanied by symptoms of hypothyroidism or in the presence of a high cardiovascular risk.
During pregnancy, failure to diagnose subclinical hypothyroidism in a timely manner can be detrimental for the course of the pregnancy, but above all for the development of the foetus. It is therefore necessary for the doctor to consider the appropriateness of starting pharmacological replacement therapy early, based on the patient’s medical history, hormone values, the presence of anti-thyroid antibodies and the findings of the thyroid ultrasound scan.
Doctors will ask patients who have been prescribed therapy to check their serum TSH values again 6-8 weeks after the start of treatment and after any dose changes, whereas patients who are not taking therapy will repeat the tests every six months in order to detect any increases in TSH levels.
REFERENCES
- Bekkering GE, Agoritsas T, Lytvyn L, Heen AF, Feller M, Moutzouri E, Abdulazeem H, Aertgeerts B, Beecher D, Brito JP, Farhoumand PD, Singh Ospina N, Rodondi N, van Driel M, Wallace E, Snel M, Okwen PM, Siemieniuk R, Vandvik PO, Kuijpers T, Vermandere M. Thyroid hormones treatment for subclinical hypothyroidism: a clinical practice guideline. 2019 May 14;365:l2006.
- Urgatz B, Razvi S. Subclinical hypothyroidism, outcomes and management guidelines: a narrative review and update of recent literature. Curr Med Res Opin. 2023 Mar;39(3):351-365.
- Jansen HI, Boelen A, Heijboer AC, Bruinstroop E, Fliers E. Hypothyroidism: The difficulty in attributing symptoms to their underlying cause. Front Endocrinol (Lausanne). 2023 Feb.
- Peeters RP, Brito JP. Subclinical hypothyroidism: to treat or not to treat? Eur J Endocrinol. 2020 Dec;183(6):D15-D24.
The information provided on the website www.feelthyroid.com is not intended as a substitute for doctor-patient relations or specialist consultations. It is advisable to always consult your doctor and/or a specialist regarding the information and guidance provided.