Hypothyroidism
Definition: Hypothyroidism is a common condition of thyroid hormone (thyroxine [T4] and tri-iodothyronine [T3]) deficiency, which are essential for normal growth, development, and metabolism. Primary hypothyroidism (95% of cases) occurs when there is thyroid hormone deficiency due to the thyroid gland being unable to produce thyroid hormones because of iodine deficiency or an abnormality within the gland itself - overt hypothyroidism, subclinical hypothyroidism and secondary hypothyroidism.
Symptoms: Primary hypothyroidism
Dry skin and hair loss
Thyroid pain, for example in subacute thyroiditis
Depression, impaired concentration and memory
Changes to appearance such as coarse dry hair and skin, and hair loss
Menstrual irregularities; infertility or subfertility
Oedema, including swelling of the eyelids
Non-specific weakness, arthralgia, and myalgia
Hoarseness or deepening of the voice; goitre
Fatigue/lethargy, cold intolerance; weight gain, constipation
Bradycardia and diastolic hypertension; pericardial effusion
Delayed relaxation of deep tendon reflexes
Paraesthesia (due to carpal tunnel syndrome) or peripheral neuropathy.
A diagnosis of other autoimmune disease
Symptoms: Other
Subclinical hypothyroidism - Clinical features of hypothyroidism are usually absent, but if present, are related to the degree of thyroid-stimulating hormone (TSH) elevation
Postpartum thyroiditis (PPT) - The hypothyroid phase of PPT usually occurs between 3–8 months (most often at 6 months) postpartum and typically lasts 4–6 months.
Secondary hypothyroidism: clinical features of primary hypothyroidism together with clinical features of possible hypothalamic-pituitary disease such as recurrent headache, diplopia, and/or visual field defects,
History
Examination
Differential Diagnosis
Any current or recent non-thyroidal illness.
Any drug treatment such as amiodarone, lithium, or over-the-counter supplements such as biotin that may affect TFTs.
Current or recent pregnancy
Any other risk factors associated with hypothyroidism.
Typical symptoms of hypothyroidism
Any possible causes of secondary hypothyroidism, such as history of brain or metastatic cancer; infiltrative disease; head trauma; surgery, radiotherapy or disease affecting the pituitary gland or hypothalamus.
Thyroid enlargement and/or thyroid nodules.
Signs of other autoimmune disease such as Addison’s disease, alopecia areata, pernicious anaemia, coeliac disease, type 1 diabetes mellitus, and vitiligo.
Possible signs or complications of hypothyroidism
Investigations
Suspect a diagnosis of subclinical hypothyroidism if TSH levels are above the normal reference range and FT4 is within the normal reference range.
Suspect hypothyroidism in pregnancy if TSH levels are elevated (using trimester-specific reference ranges) which may or may not be associated with a FT4 level below the trimester-specific reference range.
Suspect a diagnosis of primary hypothyroidism if TSH levels are above the normal reference range (usually above 10 mU/L) and FT4 is below the normal reference range.
Suspect the hypothyroid phase of postpartum thyroiditis (PPT) if TSH is raised within a year of giving birth.
Check the serum thyroid-stimulating hormone (TSH) level, using clinical judgement to interpret thryoid function test (TFT) results, especially if TFTs do not match the clinical presentation.
Suspect a diagnosis of secondary hypothyroidism if clinical features are suggestive and TSH levels are inappropriately low (may be normal), but FT4 is below the normal reference range.
Consider checking FBC, B12, HbA1c, Coeliac serology, serum lipids. Consider serum thyroid peroxidase antibodies (TPOAb) if autoimmune thyroid disease is suspected.
Suspect an alternative diagnosis if TFTs are within the normal euthyroid range.
Arrange an ultrasound of the neck to image palpable thyroid enlargement or focal nodularity in adults with normal thyroid function if malignancy is suspected.
End-organ damage such as chronic kidney disease, chronic liver disease, and heart failure
Metabolic abnormalities such as hypercalcaemia.
Haematological conditions such as anaemia and multiple myeloma
Vitamin and mineral deficiencies such as vitamin B1 deficiency, folate deficiency, iron deficiency, and vitamin D deficiency.
Endocrine/autoimmune conditions
Stress, poor sleep, alcohol misuse, anxiety, and depression.
Non-thyroidal illness
Dementia
Obesity and obstructive sleep apnoea
Post-viral syndromes and chronic fatigue and chronic fatigue syndrome
Menopause
Polymyalgia rheumatica and fibromyalgia
Carbon monoxide poisoning
Screening
Other adults: has a goitre, type 1 diabetes, dyslipidaemia, suspected dementia, radioiodine or surgery for hyperthyroidism, previous neck radiotherapy or surgery for thyroid gland for head and neck cancer, autoimmune disorders, Turner or Down's syndrome, history of postpartum thyroidItis, history of subfertillity, abnormal menstrual cycle or miscarriage, person history of preterm birth or recurrent miscarriage, taking drug treatment such as amiodarone or lithium or postnatal depression.
In pregnant women or women planning a pregnancy, if the woman: older than 30, has a goitre, has come from an area with moderate/sever iodine deficiency, previous history or current thyroid conditions, family history, type 1 diabetes, known thyroid autoantibody positive, previous miscarriage, morbidly obese.
Screening in asymptomatic adults is not recommended, however is appropriate in specific clinical situations.
Management: Overy hypothyroidism (non-pregnant)
Management: Subclinical Hypothyroidism (Non-pregnant)
Review the person and recheck TSH levels every 3 months after initiation of LT4 therapy and adjust the dose according to symptoms and TFT results. Consider checking FT4 in addition if the person has ongoing symptoms on treatment.
If a person has suspected adverse effects or feels more unwell after starting LT4 therapy: consider possible under/over treatment or consider if there is associated endocrine disease.
If specialist referral not required - treat with levothyroxine (LT4) monotherapy. Take medication on an empty stomach. Symptoms may take several weeks/months to resolve.
Once the TSH level is stable (2 similar measurements within the reference range 3 months apart), check TSH annually.
Offer advice and sources of information
If TFTs remain abnormal or the person has persistent symptoms despite adequate or escalating LT4 doses - assess for possible cause and manage appropriately, non-compliance, drug interactions, GI conditions causing malabsorption, taking LT4 with food/drink which can impair absorption, weight gain/pregnancy. - Adjust dose as appropriate.
Arrange referral or discuss with an endocrinologist, the urgency depending on clinical judgement, if the person: suspected subacute thyroiditis, goitre, nodule or structural change in the thyroid gland, suspected endocrine disease, female and planning pregnancy, atypical or difficult to interpret TFTs, suspected underlying cause of hypothyroidism.
Consider specialist referral if adequate/escalating LT4 and TSH persistently raised, persistent symptoms, or switch of medication being considered.
Arrange urgent referral to an endocrinologist for specialist assessment of the underlying cause, if secondary hypothyroidism is suspected.
Arrange emergency admission if a serious complication such as myxoedema coma is suspected.
If the person has untreated subclinical hypothyroidism or if LT4 therapy has been stopped, consider measuring TSH and FT4 - annually/ every 2-3 years.
Consider referral to an endocrinologist if there are - ongoing abnormal blood results despite treatment or persistant symptoms.
Consider offering a 6-month trial of LT4 monotherapy in adults less than 65 years of age.
Review the person and recheck TSH levels every 3 months after initiation of LT4 therapy, and adjust the dose according to symptoms and TFT results. Consider checking FT4 in addition if the person has ongoing symptoms on treatment.
Consider offering levothyroxine (LT4) monotherapy if the thyroid-stimulating hormone (TSH) level is greater than 10 mU/L and free thyroxine (FT4) level is within the reference range on 2 separate occasions 3 months apart.
Consider if specialist referral required.