Index

Background Information

There are 3 main types of hypothyroidism:

Type	Free T4	TSH
Primary overt hypothyroidism	↓	↑
Secondary overt hypothyroidism	↓	↓
Subclinical hypothyroidism	Normal	↑

Myxoedema coma is a rare, life-threatening medical emergency due to untreated severe hypothyroidism with multi-organ failure

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)

Causes can be grossly categorised into primary and secondary hypothyroidism.

Iron deficiency - 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. from surgery, radioiodine therapy, radiotherapy, anti-thyroid drugs)
Congenital hypothyroidism (most common due to thyroid gland dysgenesis)
Infiltrative disorders (e.g. amyloidosis, sarcoidosis, tuberculosis, malignant infiltration)

Essentially any cause of pituitary or hypothalamic dysfunction

Diagnosis Guidelines

NICE recommends testing for thyroid dysfunction in:

Clinically suspected cases
Type 1 diabetes or other autoimmune disease
New-onset atrial fibrillation

Choice of test:

Primary hypothyroidism suspected → TSH alone, and only measure free T4 if TSH is abnormal
Secondary hypothyroidism suspected → TSH and free T4 at the start

Type	Free T4	TSH
Primary overt hypothyroidism	↓	↑
Secondary overt hypothyroidism	↓	↓
Subclinical hypothyroidism	Normal	↑

Standard additional tests:

Anti-TPOThyroid peroxidase antibodies (consider in both primary overhypothyroidism and subclinical hypothyroidism)
FBC and serum B12 levels (to screen for prenicious 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

Summary Table

Condition	Antibody serology	Ultrasound findings	Technetium / radioiodine uptake scan
Graves’ disease	Anti-TSH receptor antibodies +ve in >90% Anti-TPO can be +ve	Diffuse enlargement ↑ Vascularity ↑ Doppler	Diffuse ↑ uptake
Toxic multinodular goitre	-ve	Multiple nodules of varying size Heterogeneous echotexture	Multifocal (patchy) ↑ uptake
Toxic adenoma	-ve	Solitary, well-defined nodule	Focal ↑ uptake (hot nodule) ↓ Uptake of remaining areas
Hashimoto’s thyroiditis	Anti-TPO +ve in >90%	Diffuse enlargement Heterogeneous hypoechoic echotexture	Diffuse ↓ uptake
Subacute (De Quervain’s) thyroiditis	-ve	Diffuse enlargement Hypoechoic areas ↓ Vascularity	Diffuse ↓ uptake
Thyroid cancer	-ve	Solid hypoechoic nodule +/- microcalcifications	Focal ↓ uptake

Management Guidelines

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.

Aim to maintain TSH within the reference range, measure TSH (adults):

Initially, every 3 months until stabilised (2 similar consecutive measurements)
Then, annually

Do not routinely offer levothyroxine in subclinical hypothyroidism.

Consider levothyroxine therapy in:

TSH ≥10 on 2 separate occasions, 3 months apart, or
Symptomatic (and elevated TSH on 2 separate occasions, 3 months apart)

See this article.

References

NICE guideline Thyroid disease: assessment and management
NICE guideline Scenario: Subclinical hypothyroidism (non-pregnant)

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Hypothyroidism

Background Information

Diagnosis Guidelines

Summary Table

Management Guidelines

References

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Hypothyroidism

Background Information

Definition

Causes

Primary Hypothyroidism Causes

Secondary Hypothyroidism Causes

Diagnosis Guidelines

Clinical Features (to be added)

Investigation and Diagnosis

Thyroid Function Test Interpretation

Further Testing

Summary Table

Comparison of Common Thyroid Disorders (Test Interpretation)

Management Guidelines

Primary Overt Hypothyroidism

Monitoring

Subclinical Hypothyroidism

Hypothyroidism in Pregnancy

References

Original Guideline