Diagnosis

Classic symptoms of hypothyroidism include fatigue, weight gain, cold intolerance, arthralgia, constipation, menorrhagia, and dry skin and hair.

Physical signs include pallor, coarse skin and hair, bradycardia and goitre, but may be absent in mild hypothyroidism. These symptoms and signs are non-specific and common in people without thyroid disease, so laboratory diagnosis is required.

Serum TSH should be measured; if this is in the reference range, then additional tests such as free thyroxine (T4), free triiodothyronine (T3) or thyroid antibodies are rarely helpful.

Treatment

Thyroid hormone replacement is indicated for overt hypothyroidism and for subclinical hypothyroidism with TSH levels above 10 mU/L.

Patients with persistent mild subclinical hypothyroidism (TSH, 4–10 mU/L) and minimal or no symptoms can be offered a choice between thyroxine treatment or observation with annual follow-up testing to detect progressive hypothyroidism. 

Thyroxine/Levothyroxine is the standard treatment for hypothyroidism. The usual approach is an initial dose of 50–100 μg/day with subsequent titration based on thyroid function tests checked 6–8 weeks later. Smaller initial doses (25 μg/day) should be used in very frail or elderly patients and in those with symptomatic ischaemic heart disease.

Ideally, thyroxine/ levothyroxine should be taken in a fasting state, 1 hour before breakfast, but this may be inconvenient and reduce adherence, and it is probably more important that daily dosing is consistent with regard to time of day and relationship to meals.

Thyroid replacement therapy is not indicated for individuals with symptoms suggestive of hypothyroidism if TSH levels are within the reference interval.

Overt hyperthyroidism

Hyperthyroidism is less common than hypothyroidism. The clinical picture is often characteristic, with symptoms including weight loss, heat intolerance, palpitations, breathlessness, anxiety, diarrhoea, tremor and proximal muscle weakness. Physical signs include tremor, tachycardia, ophthalmopathy, goitre and difficulty rising from a squatting position.

Diagnosis

The diagnosis is confirmed by thyroid function tests showing suppressed TSH (usually undetectable) with elevated free T4 and/or free T3.

Hyperthyroidism is most commonly caused by Graves’ disease, thyroiditis or toxic nodular goitre.

Treatment

It is important to establish the cause of hyperthyroidism before starting treatment.

Graves’ disease should be treated initially with carbimazole (15–20 mg daily for mild to moderate hyperthyroidism, 30–40 mg for severe hyperthyroidism). In patients who respond well, it can be continued for an 18-month course, aiming for long term remission. Other treatment options are radioactive iodine treatment and thyroidectomy.

Toxic nodular goitre can be treated with surgery or radioactive iodine. Antithyroid drugs can be used, but need to be continued lifelong as remission of hyperthyroidism is unlikely, and are not the preferred option.

Subclinical hyperthyroidism

Mild subclinical hyperthyroidism, with TSH levels between 0.1 and 0.4 mU/L, may be caused by autonomous thyroid nodules but may also be found in healthy individuals (healthy outliers). It often resolves without treatment, so follow-up with repeat testing may be all that is required. 

Palpable thyroid nodules

Palpable thyroid nodules are present in about 5% of the population. Most are benign, commonly colloid nodules, cysts, nodular thyroiditis or benign neoplasm, whereas about 5% are malignant.

Large nodular goitres can be symptomatic and require surgery for relief of pressure symptoms, but most thyroid nodules are asymptomatic, and the diagnostic work-up is aimed at assessing the risk of thyroid cancer.

TSH levels should be measured but are usually normal, and the key investigation is ultrasound-guided fine needle aspiration (FNA) biopsy.