Hypothyroidism
NICE CKS Hypothyroidism. Last revised: Nov 2024.
NICE guideline [NG145] Thyroid disease: assessment and management. Last updated: Oct 2023.
Background Information
Definition
Hypothyroidism is defined as the deficiency of thyroid hormone (thyroxine T4 and tri-iodothyronine T3).
Aetiology
Primary Hypothyroidism Causes
- Iodine deficiency (dietary) – most common worldwide cause
- Autoimmune thyroiditis – most common cause in the UK (and other iodine-sufficient areas)
- Hashimoto’s thyroiditis
- Atrophic thyroiditis
- Transient thyroiditis
- De Quervain’s (subacute) thyroiditis
- Postpartum thyroiditis
- Iatrogenic (e.g. thyroidectomy, radioiodine therapy, radiotherapy, anti-thyroid drugs)
- Congenital hypothyroidism (most common due to thyroid gland dysgenesis)
- Infiltrative disorders (e.g. amyloidosis, sarcoidosis, tuberculosis, malignant infiltration)
Secondary Hypothyroidism Causes
Essentially any cause of pituitary or hypothalamic dysfunction
Complications
Acute complication: myxoedema coma
- Rare, life-threatening medical emergency due to untreated severe hypothyroidism with multi-organ failure
- Presents with bradycardia, hypothermia, coma, seizures
Do not mix myxoedema coma up with the following terms:
- Myxoedema: generalised thickening and swelling of the skin and subcutaneous tissue due to the accumulation of mucopolysaccharides in the dermis. This is caused by long-standing hypothyroidism
- Pretibial myxoedema: localised dermopathy over the shins in Graves’ disease (autoimmune-induced overproduction of glycosaminoglycans)
Long-term complications:
- Coronary artery disease
- Stroke
- Heart failure
- Pregnancy
- Risk of congenital hypothyroidism (if inadequately treated)
- Increased risk of miscarriage, anaemia, pre-eclampsia, placental abruption, postpartum haemorrhage, and stillbirth
Diagnosis
Clinical Features
Shared / Non-Specific Features
The clinical features of hypothyroidism are mapped to a thyroid examination (starting from the periphery, then top to bottom).
| Body system | Clinical features |
|---|---|
| General (screening questions) |
|
| Hands |
|
| Pulse and BP |
|
| Skin changes | Non-specific skin changes:
Skin changes from generalised myxoedema
|
| Neck |
|
| Abdomen |
|
| Lower limb |
|
Secondary hypothyroidism will also have features of hypothalamic-pituitary diseases, e.g. headache, bitemporal hemianopia, diplopia.
Cause-Specific Features
Iodine Deficiency
Iodine deficiency typically presents with a goitre (diffuse thyroid enlargement)
Hashimoto’s Thyroiditis
Hashimoto’s thyroiditis typically presents with a painless, firm goitre (diffuse thyroid enlargement)
Hashitoxicosis may occur before the onset of hypothyroidism: transient thyrotoxicosis due to rupture of hormone-containing follicles
De Quervain (Subacute) Thyroiditis
Classically presents with preceding URTI and a tender diffuse goitre +/- radiation to the jaw / ear [Ref]
De Quervain thyroiditis classically presents with a triphasic phase: [Ref]
- Thyrotoxic phase – manifests as thyrotoxicosis (for 3-6 weeks, in ~50% patients)
- Hypothyroid phase – manifests as hypothyroidism (typically for ≤6 months, in ~30% patients and ~15% patients stay hypothyroid permanently)
- Euthyroid phase – return back to normal
A goitre that is painful is almost always de Quervain thyroiditis, as other causes of a goitre are almost always painless.
Investigation and Diagnosis
NICE recommends testing for thyroid dysfunction in:
- Clinically suspected cases
- Type 1 diabetes or other autoimmune disease
- New-onset atrial fibrillation
Thyroid Function Test Interpretation
| Type | Free T4 | TSH |
|---|---|---|
| Primary overt hypothyroidism | ↓ | ↑ |
| Secondary overt hypothyroidism | ↓ | ↓ |
| Subclinical hypothyroidism | Normal | ↑ |
Further Testing
Standard additional tests:
- Anti-TPO antibodies (consider in both primary overt hypothyroidism and subclinical hypothyroidism)
- FBC and serum B12 levels (to screen for pernicious anaemia)
- HbA1c (to screen for type 1 diabetes)
- Coeliac serology (to screen for coeliac disease)
- Serum lipids (to assess for associated dyslipidaemia)
If there is palpable thyroid enlargement or focal nodularity → ultrasound neck
In patients in subclinical hypothyroidism, the most important additional test is anti-TPO antibodies.
+ve Anti-TPO indicates that these patient are more likely to progress into overt hypothyroidism.
Summary Table
Comparison of Common Thyroid Disorders (Test Interpretation)
| Condition | Antibody serology | Ultrasound findings | Technetium / radioiodine uptake scan |
|---|---|---|---|
| Graves’ disease |
|
|
|
| Toxic multinodular goitre |
|
|
|
| Toxic adenoma |
|
|
|
| Hashimoto’s thyroiditis |
|
|
|
| Subacute (De Quervain’s) thyroiditis |
|
|
|
| Thyroid cancer |
|
|
|
Management
Primary Overt Hypothyroidism
Offer levothyroxine
Recommended doses:
- ≥65 y/o with history of cardiovascular disease: start with 25-50 mcg per day
- Other patients: 1.6 mcg/kg (rounded to nearest 25 mcg)
- = 125 mcg per day for a 70kg adult
Patient should be advised to take levothyroxine first thing in the morning on an empty stomach before other food or medications.
Note that transient thyroiditis (i.e. De Quervain’s and postpartum thyroiditis) do not require routine levothyroxine therapy as they are usually self-limited.
Monitoring
Aim to maintain TSH within the reference range, measure TSH (adults):
- Initially, every 3 months until stabilised (2 similar consecutive measurements)
- Then, annually
Subclinical Hypothyroidism
Do not routinely offer levothyroxine in subclinical hypothyroidism.
Consider levothyroxine therapy in:
- TSH ≥10 mU/L on 2 separate occasions, 3 months apart, or
- Symptomatic (and elevated TSH, but <10 mU/L on 2 separate occasions, 3 months apart)
Hypothyroidism in Pregnancy
See the Thyroid Disorders in Pregnancy article.
References