Hypothyroidism – An Overview

 

Hypothyroidism – An Overview

 

What is hypothyroidism?

This is when the thyroid produces less thyroid hormone than it should which causes the metabolism to run too slow.  This is called hypothyroidism, myxoedema or an underactive thyroid. It may also be called Hashimoto’s disease.

Subclinical hypothyroidism (borderline hypothyroidism) is when patients have symptoms of hypothyroidism but only one of the thyroid tests is abnormal – the thyroid stimulating hormone (TSH) test.1

The thyroid system is complex. The thyroid is part of the endocrine system which includes the pituitary.

The pituitary produces a hormone called thyroid stimulating hormone (TSH) which stimulates the thyroid to produce thyroxine (T4).  Thyroxine is inactive and needs to be converted by the tissues and organs of the body into the active hormone, triiodothyronine (T3).

Hypothyroidism is mostly seen in women between the ages of 40-50 and is seen in women ten times more often than men.2  It often occurs during the menopausal years and symptoms are often ignored during the early stages by both patients and doctors if the patient is at this age.

The prevalence of hypothyroidism is 1-2% (approximately 2 in every 100 people) but some doctors feel that the rate is much higher than this.3

Subclinical hypothyroidism is found in 8–10% of the population, is more common in women and increases with age.4

 

What causes it?

The main causes of an underactive thyroid are:

  • Hashimoto’s disease  –  an autoimmune disease where the antibodies may first stimulate the thyroid and then destroy it 4
  • genetic dysfunction – the thyroid may be dysfunctional at birth (congenital hypothyroidism) 5, or there is a polymorphism (a gene that is different to usual) that isn’t found until the person is an adult 6
  • pituitary or hypothalamic failure, causing secondary hypothyroidism (central hypothyroidism) 5
  • iodine or selenium deficiency 5,7
  • environmental challenges or deficiencies – chemicals and some foods and drinks can cause problems for the thyroid 8,9
  • previous thyroid surgery (thyroidectomy) or radioactive iodine treatment 5
  • drug treatment for hyperthyroidism 5
  • certain drugs can cause hypothyroidism 5
  • inability to absorb synthetic levothyroxine adequately 10
  • lack of conversion from T4 to T3 10
  • receptor resistance 12

 

What are the symptoms?

There are many signs and symptoms of an underactive thyroid, the main ones being: 13,14,15,16,17,18

  • fatigue/lethargy
  • weight gain, even though you eat less
  • cold intolerance
  • muscle weakness, arthralgia, myalgia
  • constipation
  • menstrual problems
  • depression
  • impaired concentration and memory
  • hair loss body, scalp and eyebrows
  • hoarse voice/deepening of voice
  • goitre, difficulty swallowing
  • delayed relaxation of deep tendon reflexes
  • loss of libido
  • fertility problems
  • raised cholesterol
  • breathlessness
  • dry/gritty eyes

See Signs and Symptoms of Hypothyroidism for full list.

 

What tests are used to diagnose hypothyroidism?

Blood tests should reveal whether the thyroid gland is underactive although some doctors may not do all the blood tests available.

There are several thyroid tests that can be done to diagnose hypothyroidism: 19

  • TSH (thyroid stimulating hormone)
  • FT4 (FreeT4)
  • FT3 (FreeT3)
  • TPO (thyroid peroxidase antibody)
  • TgAb (thyroglobulin antibody)

However, the TSH test is often the only test performed by doctors which means there is a possibility that autoimmune hypothyroidism and secondary hypothyroidism may be missed.

Some doctors think that this test is not suitable on its own because it is an indirect test and not a true thyroid hormone test.  The (now archived) guidance, “UK Guidelines for the Use of Thyroid Function Tests20 state that although a TSH test “may be cost effective for a wide range of clinical purposes it may be inappropriate in patients being tested for the first time, and in some specific clinical settings.”  These guidelines say that TSH and FT4 should be done when optimising levothyroxine therapy in newly diagnosed patients with hypothyroidism, diagnosing and monitoring thyroid disorders in pregnancy and monitoring patients with hyperthyroidism in the early months after treatment.

These guidelines also say that both tests should be done in rare situations such as central hypothyroidism, end-organ thyroid hormone resistance and TSH-secreting pituitary adenomas and “if clinical details are not available that allow the identification of the above categories of patient, then it may be prudent for laboratories to measure serum TSH and FT4 on all specimens rather than embark on a first-line serum TSH testing strategy followed by a cascade to include FT4 and FT3 if indicated.”

In our experience, many doctors are not aware of either the rarer forms of hypothyroidism or these particular sections of the guidelines.  Therefore, it might be an idea to discuss the guidelines with your GP even though they are archived.

Unfortunately, more recent guidance doesn’t clarify that FT4 testing should be done, even if the patient is on liothyronine (synthetic T3). 21,22

Thyroid UK feels that in many instances, patients should be referred to an endocrinologist to check for central hypothyroidism and other thyroid disorders. However, patients are very rarely referred to an endocrinologist for hypothyroidism as it is considered that the GP can deal with treatment.

 

What test results would give a diagnosis of hypothyroidism?

A level of FT4 below the reference range together with a TSH level above the reference range will usually give a diagnosis of hypothyroidism.

However, the “UK Guidelines for the Use of Thyroid Function Tests” state that, “There is no evidence to support the benefit of routine early treatment with thyroxine in non-pregnant patients with a serum TSH above the reference range but <10mU/L (II,B). Physicians may wish to consider the suitability of a therapeutic trial of thyroxine on an individual patient basis.”  Therefore, many doctors will not diagnose hypothyroidism until a patient’s TSH level is more than 10.  If your TSH is above the range but less than 10, discuss a therapeutic trial of levothyroxine with your doctor.

There is controversy in regard to when a patient is classed as hypothyroid and whether they should be treated or not.

Experts don’t all agree what level of TSH should enable patients to be treated.  Some feel that a level to 2.5 23 should be the point at which patients should be treated.

If you suspect you may have hypothyroidism or subclinical hypothyroidism we have lots of other articles that you may find useful:

 

Check out what people are saying on our online community regarding hypothyroidism:

http://www.healthunlocked.com/thyroiduk

 

Thyroid UK relies on donations so that we can continue to support and campaign for people with thyroid disease and related disorders.  If you have found our information helpful, please do think about donating or becoming a member.

 

Donate

Become a member

 

 

Glossary

 

Autoimmune – patients with autoimmune diseases frequently have antibodies circulating in their blood that target their own body tissues

Endocrinologist – a medical practitioner qualified to diagnose and treat disorders of the endocrine glands and hormones

Goitre – a swelling of the neck resulting from enlargement of the thyroid gland

Hashimoto’s disease – an autoimmune disease causing chronic inflammation and consequential failure of the thyroid gland

Hypothalamic failure – a problem (or) condition with the region of the brain known as the hypothalamus, which helps to control and regulate body functions of pituitary gland like adrenal glands, ovaries, testes, thyroid gland

Levothyroxine – a synthetic thyroid hormone commonly given to treat an underactive thyroid. It is also known as L-thyroxine

Metabolism – the chemical processes within the human body

Pituitary – of or relating to the pituitary gland

Thyroidectomy – the removal of all (total) or part (partial) of the thyroid gland

Thyroid stimulating hormone – produced by the pituitary gland its role is to regulate the production of hormones by the thyroid gland

Thyroxine – the main hormone secreted into the bloodstream by the thyroid gland. It is the inactive form

Triiodothyronine – alternative name is T3. Triiodothyronine is the active form of the thyroid hormone, thyroxine

TSH-secreting pituitary adenomas – benign tumours of the pituitary gland. They produce too much thyroid stimulating hormone (TSH), which causes the thyroid gland to enlarge and produce thyroid hormone in excess, leading to an overactive thyroid (hyperthyroidism)

 

References

  1. Thyroid hormones treatment for subclinical hypothyroidism: a clinical practice guideline
    G E Beckering et al
    BMJ 2019;365:l2006
    https://www.bmj.com/content/365/bmj.l2006
  2. Hypothyroidism and myxedema coma
    Erik D Schraga, MD et al
    Medscape
    https://emedicine.medscape.com/article/768053-overview#a6
  3. Management of primary hypothyroidism: statement by the British Thyroid Association Executive Committee
    Onyebuchi Okosieme et al
    Clinical Endocrinology (2015), 0, 1–10
    https://www.british-thyroid-association.org/sandbox/bta2016/bta_statement_on_the_management_of_primary_hypothyroidism.pdf
  4. Subclinical thyroid disease
    Anukul Garg, Mark P.J. Vanderpump
    British Medical Bulletin, Volume 107, Issue 1, September 2013, Pages 101–116,
    https://academic.oup.com/bmb/article/107/1/101/258824
  5. Underactive thyroid (hypothyroidism) – Causes
    NHS
    https://www.nhs.uk/conditions/underactive-thyroid-hypothyroidism/causes/
  6. Genetics of Thyroid Function and Disease
    Panicker V
    Clin Biochem Rev. 2011 Nov; 32(4): 165–175
    https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3219766/
  7. Selenium and Thyroid Disease: From Pathophysiology to Treatment
    Mara Ventura,  Miguel Melo and Francisco Carrilho
    Int J Endocrinol. 2017; 2017: 1297658.
    https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5307254/
  8. Thyroid Disrupting Chemicals
    Valeria Calsolaro et al
    Int J Mol Sci. 2017 Dec; 18(12): 2583.
    https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5751186/
  9. Various Possible Toxicants Involved in Thyroid Dysfunction: A Review
    Jagminder K. BajajPoonam Salwan, and Shalini Salwan
    J Clin Diagn Res. 2016 Jan; 10(1): FE01–FE03.
    https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4740614/
  10. Treatment of Thyroxine Malabsorption
    J Kempke, H Hussain, B Bhan, L Graves
    Journal of Endocrinology and Metabolism, Volume 5, Number 1-2, April 2015
    https://jofem.org/index.php/jofem/article/view/277/332
  11. Abnormalities of Thyroid Hormone Metabolism during Systemic Illness: The Low T3 Syndrome in Different Clinical Settings
    A M Neto, D E Zantut-Wittmann
    International Journal of Endocrinology, 2016
    https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5075641/
  12. Society for Endocrinology
    https://www.yourhormones.info/endocrine-conditions/resistance-to-thyroid-hormone/
  13. British Thyroid Foundation
    http://www.btf-thyroid.org/information/leaflets/29-hypothyroidism-guide
  14. Underactive thyroid (hypothyroidism) – Symptoms
    NHS
    https://www.nhs.uk/conditions/underactive-thyroid-hypothyroidism/symptoms/
  15. Goitre
    NHS
    https://www.nhs.uk/conditions/goitre/
  16. You and your Hormones – Goitre
    Society for Endocrinology
    https://www.yourhormones.info/endocrine-conditions/goitre/
  17. A Classic Sign of Hypothyroidism
    S Cyriac et al
    CMAJ, 2008 Aug 12; 179(4): 387
    https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2492977/
  18. Pulmonary consequences of hypothyroidism
    S H Sadek, W A Khalifa, A M Azoz
    Ann.Thorac.Med. 2017 Jul-Sep; 12(3): 204–208
    https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5541969/
  19. Presence of Dry Eye in Patients with Hashimoto’s Thyroiditis
    E Kan et al
    Journal of Ophthalmology, Volume 2014, Article ID 754923
    https://www.hindawi.com/journals/joph/2014/754923/
  20. Thyroid Function Tests
    American Thyroid Association
    https://www.thyroid.org/thyroid-function-tests/
  21. UK Guidelines for the use of Thyroid Function Tests
    British Thyroid Foundation
    http://www.btf-thyroid.org/images/documents/tft_guideline_final_version_july_2006.pdf
  22. Clinical Practice Guidelines for Hypothyroidism in Adults
    J R Garber et al
    American Association of Clinical Endocrinologists and American Thyroid Association
    https://journals.aace.com/doi/pdf/10.4158/EP12280.GL
  23. Underactive thyroid: Deciding whether or not to treat subclinical hypothyroidism
    National Center for Biotechnology Information (NCBI)
    https://www.ncbi.nlm.nih.gov/books/NBK279600/

 

Date created: 22/08/2019 (V1.3)
Review date:  22/08/2021