A 46 year old woman has returned to you for the results of blood tests. Two weeks earlier she had complained of increasing tiredness, constipation, dry skin, and weight gain. Thyroid function tests at her previous consultation showed concentrations of free levothyroxine (T4) of 7 nmol/l and of thyroid stimulating hormone (TSH) of 38 mU/l. Her mother had Graves' disease and was treated with radioiodine ablation.

What issues you should cover

Underlying causes--The commonest cause of primary hypothyroidism is autoimmune thyroiditis. Hashimoto's thyroiditis is the combination of autoimmune thyroiditis and goitre; a positive test result for the thyroid autoantibodies antithyroglobulin and antiperoxidase will confirm the diagnosis. An enlarged, tender thyroid may indicate subacute thyroiditis.

Current and previous drug use--Amiodarone, lithium, interferon alfa, interleukin 2, macrophage colony stimulating factor, and oral and topical iodine are recognised causes of thyroid dysfunction. Check for history of thyroid surgery or head and neck irradiation and radioactive iodine therapy for thyrotoxicosis.

Menstrual and obstetric history, including amenorrhoea and menorrhagia--A self limiting period of hypothyroidism is common in the course of subacute thyroiditis and in the syndrome of "painless thyroiditis," including the postpartum variant. In these cases transient biochemical hypothyroidism does not warrant treatment unless the symptoms are severe.

Psychological needs--Assess her psychological needs and, if necessary, provide information on access to a specialist nurse or a patients' self help group.

Indications for referral of adults with hypothyroidism to a specialist

Pregnant or post partum
Evidence of pituitary disease
Ischaemic heart disease
Treatment with amiodarone or lithium

What you should do

• Examine her neck for presence or absence of goitre or a thyroidectomy scar. Examine her generally for features of associated organ specific autoimmune diseases, such as vitiligo, and assess her cardiovascular and nervous systems for bradycardia, proximal weakness, peripheral neuropathy, carpal tunnel syndrome, and Pemberton's sign.
• Examining her eyes for thyroid associated ophthalmopathy may give a clue to the underlying cause. It is more common in Graves' disease (>90% of patients) but can occur in patients with chronic autoimmune thyroiditis (4-9%). Signs include proptosis, periorbital oedema, conjunctival injection and oedema, restrictive extraocular myopathy, and exposure keratitis.
• The investigation should include fasting lipid profile, fasting glucose, glycosylated haemoglobin, and tests for organ specific autoimmune diseases. Primary hypothyroidism is associated with hypercholesterolaemia, and type 1 diabetes mellitus and pernicious anaemia are more common in patients with autoimmune thyroid disease. Only certain patients will need to be referred to a specialist for isotope uptake studies and thyroid antibody assays (see box).
• Prescribe oral levothyroxine 50-100 µg daily. The initial dose in patients with ischaemic heart disease should be 25 µg daily. Diarrhoea, nervousness, rapid pulse, insomnia, tremors and, sometimes, anginal pains indicate the dose is too high. Reduce the dose or stop treatment for one or two days and start again at a lower dose.
• You will need to monitor treatment with tests of serum TSH concentrations. When the concentration is within the reference range the T4 concentration will usually be in the upper half or slightly above the reference range. If you change the levothyroxine dosage, no measurement of TSH concentration or further dosage change should be made for 4-6 weeks, because the half life of TSH is about 10 days and changes in dosage will be reflected slowly in serum TSH concentrations.
• Discuss and agree a clear treatment and monitoring plan with her. Explain that treatment is likely to be life long, that treatment at the correct dosage has no serious side effects, and that the prognosis is excellent. Tell her it may take a few weeks for levothyroxine to start working and that she should not expect all symptoms to disappear within a few days of starting treatment.
• Tell her that she is entitled to free prescriptions and to fill in the prescription charge exemption certificate.

T A Bajwa general practitioner, Figges Marsh Surgery, Mitcham CR4 2AD

studentBMJ 2005;13:1-44 January ISSN 0966-6494

Websites with information on thyroid disorders

Thyroid UK, a support group for patients (www.thyroiduk.org)

The US site About.com has excellent information (www.thyroid.about.com)

British Thyroid Foundation (www.btf-thyroid.org)

The Royal National Institute for the Blind website's "Eye info" section has information on thyroid eye disease (www.rnib.org.uk)

Further reading

Dayan CM, Daniels GH. Chronic autoimmune thyroiditis. N Engl J Med 1996;335:99-107

Lindsay RS, Toft AD. Hypothyroidism. Lancet 1997;349:413-6

Vanderpump MPJ, Ahlquist JAO, Franklyn JA, Clayton RN. Consensus statement for good practice and audit measures in the management of hypothyroidism and hyperthyroidism. BMJ 1996;313:539-44

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