Hypothyroidism

Table of contents
Key points ⚡
Succinct notes to superpower your revision
Hypothyroidism\: insu
Hashimoto’s thyroiditis.
Thyroid gland\: butter
Thyroid hormones\: regulate metabolism, weight, temperature, hair growth, nails, and skin; controlled by the hypothalamic-
pituitary-thyroid (HPT) axis.
Causes\:
Primary\: Hashimoto’s, iodine de
iatrogenic (medications, surgery, radiotherapy).
Secondary\: pituitary tumours.
Risk factors\: family history, recent pregnancy, autoimmune diseases (e.g., diabetes, rheumatoid arthritis), previous thyroid
surgery or radioactive iodine treatment, radiation to head/neck/thorax.
Symptoms\: weight gain, constipation, depression, brittle hair/nails, irregular/heavy periods, loss of libido, lethargy, cold
intolerance.
Clinical
Investigations\:
Blood tests\: TSH (elevated in primary, low/normal in secondary), free T4 (low).
Autoantibodies\: anti-TPO (positive in Hashimoto’s).
Imaging\: Doppler ultrasound for nodules/in
Management\: hormone replacement therapy with levothyroxine; monitor thyroid function tests every three months initially,
then annually once stable.
Complications\:
Myxoedema coma\: altered mental state, hypothermia, bradycardia, hypoventilation; treated with thyroid replacement,
glucocorticoids, supportive measures.
Cardiac complications\: heart disease (coronary artery disease, heart failure, atherosclerosis) due to elevated serum
cholesterol.
Reproductive complications\: sub-fertility, increased risk of miscarriage, stillbirth, pre-eclampsia, postpartum haemorrhage.
Article 🔍
A comprehensive topic overview

Introduction

Hypothyroidism occurs when there is insu
the body's demands.
The most common cause of hypothyroidism in developed populations is an autoimmune condition, Hashimoto’s
thyroiditis, which results in the underproduction of endogenous thyroid hormones.
1Aetiology
Anatomy
The thyroid gland is a butter
aspect of the neck at the level of C5-T1.
2
Normal physiology
Thyroid hormones have a wide range of functions, including regulating basal metabolic rate, weight, internal temperature,
hair growth, nail health and skin condition.
The synthesis of these thyroid hormones is regulated by the hypothalamic-pituitary-thyroid (HPT) axis (Figure 1).
Thyrotropin-releasing hormone (TRH), produced by the hypothalamus, stimulates the production of thyroid-stimulating
hormone (TSH) from the anterior pituitary gland.
TSH binds to the thyroid gland surface receptors and stimulates the production of T3 (triiodothyronine) and T4 (thyroxine)
thyroid hormones, which are produced from the follicular cells of the thyroid gland.
3
The HPT axis is regulated by a negative feedback loop whereby a decrease in thyroid gland hormones signals the
hypothalamus and anterior pituitary to synthesise more TRH and TSH hormones. However, in hypothyroidism, the HPT axis
becomes deranged.
Figure 1. Thyroid hormonal axis diagram
Causes of hypothyroidism
Hypothyroidism can be strati
4
Primary hypothyroidism refers to thyroid hormone underproduction caused by the thyroid gland itself
Secondary hypothyroidism refers to thyroid hormone underproduction caused by the structures/factors external to the
thyroid gland
Hashimoto’s disease (autoimmune)
Hashimoto’s (autoimmune) thyroiditis is the most common cause of hypothyroidism in Western populations. Anti-thyroid
peroxidase antibodies (anti-TPO) attack the thyroid gland, impairing the gland’s ability to produce thyroid hormones.
It is most common in women aged 30 to 50 and is four to ten times more common in women than men. Individuals with
other autoimmune conditions, such as diabetes and rheumatoid arthritis, are more likely to develop autoimmune
thyroiditis.
5
Iodine de
Iodine de6
Iodine is a key component of thyroxine (T4)
and triiodothyronine (T3). Therefore, a de
Congenital hypothyroidism
Congenital hypothyroidism is a condition present from birth where the thyroid gland is underdeveloped or absent,
resulting in thyroid hormone de
developmental delay.
7
Pituitary tumoursPituitary tumours such as pituitary adenomas can cause central hypothyroidism by compressing the pituitary gland or
interrupting the gland’s blood
hypothyroidism due to a lack of stimulation to produce the thyroid hormones.
8
De Quervain’s thyroiditis
De Quervain’s thyroiditis is a transient in
hypothyroidism and euthyroidism. It is usually triggered by a virus and is a self-limiting condition.
9
Post-partum thyroiditis
Following the relative immunosuppressive state of pregnancy, thyroid gland in
Classically, this is triphasic\: hyperthyroidism, hypothyroidism and euthyroidism. However, the hypothyroid period of this
condition may persist in 20-30% of cases.
10
Iatrogenic
Iatrogenic causes such as medications, sphenoid surgery and radiotherapy to the brain may also cause hypothyroidism.
Medications that commonly cause hypothyroidism include amiodarone and lithium.
11

Risk factors

Risk factors for hypothyroidism include\:
12
A family history of hypothyroidism
Pregnancy in the last six months
Autoimmune diseases such as type 1 or 2 diabetes, coeliac disease and rheumatoid arthritis
Previous thyroid surgery or treatment with radioactive iodine
Radiation treatment to the head, neck or thorax

Clinical features

History
Typical symptoms of hypothyroidism include\:
Weight gain
Constipation
Depression
Brittle hair and nails
Irregular or heavy periods
Loss of libido
Lethargy
Cold intolerance
Other important areas to cover in the history include\:
Obstetric history\: current or recent pregnancy
Drug history\: to identify any drugs which may cause hypothyroidism (e.g. lithium)
Past medical history\: history of other autoimmune conditions (e.g. rheumatoid arthritis)
Family history\: thyroid or autoimmune disease
Clinical examination
All those presenting with symptoms suggestive of hypothyroidism should have a thyroid status examination.
Typical clinical
13
Dry skin
Bradycardia
Cold peripheries
Sti
Hertoghe’s sign
Hertoghe’s sign (also called Queen Anne's sign), the loss of the outer third of the eyebrow, is a rare sign of
hypothyroidism (Figure 2).
Figure 2. Hertoghe's sign in
hypothyroidism

Investigations

Thyroid function tests (TFTs)
Thyroid function blood tests, including TSH, free T3 and free T4, should be performed when investigating potential thyroid
conditions. In hypothyroidism, these tests will show a low free T3 and low free T4.
In primary hypothyroidism, the HPT axis will attempt to correct the de
secondary causes, this will be low or normal due to reduced pituitary production of TSH.
14
For more information, see the Geeky Medics guide to thyroid function test interpretation.
Figure 3. TFT interpretation
Autoantibody testing
Testing for autoantibodies such as anti-thyroid peroxidase (anti-TPO) can aid the identi
conditions. TPO antibodies are found in 90% of people with Hashimoto’s thyroiditis. However, they may also be present in
Grave’s thyrotoxicosis.
15
Imaging
Doppler ultrasound can visualise the thyroid gland to assess for nodules and/or in

Management

First line management of hypothyroidism is hormone replacement therapy with levothyroxine, a synthetic T4 hormone.Individuals usually take this life-long, and thyroid function tests should be performed every three months to titrate the
medications appropriately. Following a stable TSH level, thyroid function tests should be performed annually.

Complications

Myxoedema coma
Myxoedema coma is a rare and potentially fatal complication of hypothyroidism presenting with altered mental state,
hypothermia, bradycardia, and hypoventilation. This is a medical emergency which must be treated rapidly under specialist
endocrine input with thyroid replacement therapy, glucocorticoid therapy, and supportive measures.
16
Cardiac complications
Individuals with hypothyroidism are at risk of heart disease, including coronary artery disease, heart failure and
atherosclerosis, due to its association with elevated serum total and LDL cholesterol.
17
Reproductive complications
Overt hypothyroidism is also associated with sub-fertility and may increase the risk of miscarriage, stillbirth, pre-eclampsia
and postpartum haemorrhage in pregnancy.
18

References

Parveen K, Michael C. K u m a r a n d C l a r k’ s C l i n i c a l M e d i c i n e . 9 ed. London\: Elsevier; 2017
Netter FH. Atlas of human anatomy. Philadelphia, PA\: Elsevier; 2011.74 – 80p
Lingvay I and Holt S. Textbook of Endocrine Physiology. 5th ed. New York\: Oxford Academic; 2011. 311-345p
Owen K, Turner H, H. WJA. Oxford Handbook of Endocrinology and Diabetes. Oxford\: Oxford University Press; 2022
Hashimoto’s disease. 2021. Available from\: [LINK]
World Health Organization. Iodine deLINK]
PIER Network. Management of raised neonatal bloodspot TSH and initial management of congenital hypothyroidism. 2020.
Available from\: [LINK]
BMJ Best Practice. Central hypothyroidism. 2023. Available from\: [LINK]
BMJ Best Practice. Subacute thyroiditis. 2023. Available from\: [LINK]
Epp R, Malcolm J, Jolin-Dahel K, Clermont M, Keely E. Postpartum thyroiditis. British Medical Journal Publishing Group; 2021.
Available from\: [LINK]
Kavanagh S, Boparai P. Thyroid dysfunction and drug interactions. The Pharmaceutical Journal. 2015. Available from\: [LINK]
Chaker L, Razvi S, Bensenor I et al. Hypothyroidism. Nature Reviews Disease Primers. 2022; 8 (30).
Fisher D, Wittner L, Gill D. Oxford Clinical Guidelines\: Newly quali
Starr O, Tidy C. T h y r o i d F u n c t i o n T e s t s . 2020. Available from\: [LINK]
Fröhlich E, Wahl R. Thyroid autoimmunity\: Role of anti-thyroid antibodies in thyroid and extra-thyroidal diseases. Frontiers in
Immunology. 2017;8.
Willacy D. Myxoedema Coma\: Causes, symptoms, treatment. Patient Info. 2022. Available from\: [LINK]
Mayer O, Šimon J, Filipovský J, Plášková M, Pikner R. Hypothyroidism in coronary heart disease and its relation to selected
risk factors. Vascular Health and Risk Management. 2006;2(4)\:499–506.
NICE CKS. H y p e r t h y r o i d i s m \: C o m p l i c a t i o n s . Available from\: [LINK]
Image references
Figure 1. Geeky Medics.
Figure 2. Jane Kobylianskii and Wayne L Gold. Q u e e n A n n e S i g n . License\: [CC BY-NC-ND]Reviewer
Dr Juliane Kause

Acromegaly
Addison's Disease (Primary Adrenal Insu
Cushing's Syndrome
Diabetes Insipidus
Growth Hormone De

Hypothyroidism

Introduction

Risk factors

Clinical features

Investigations

Management

Complications

References

Test yourself

Contents

Hypothyroidism

Introduction

Risk factors

Clinical features

Investigations

Management

Complications

References

Related notes

Test yourself

Contents