A 70-year-old on treatment for cardiac failure has TSH 50 µIU/mL with suppressed T3 and T4, constipation, cold intolerance and considerab…

Establish the diagnosis and its cause before prescribing. This is overt primary hypothyroidism — a markedly elevated TSH with low free T4. The most frequent cause of hypothyroidism in old age is autoimmune thyroiditis, followed by earlier thyroid surgery or radiation therapy for previous thyrotoxicosis. Confirm with free T4 and antithyroid (anti-TPO) antibodies. In this patient specifically, ask about amiodarone — a common drug in heart failure and a classic cause of hypothyroidism — and about lithium, and check the lipid profile, creatine kinase (often raised), haemoglobin (normocytic anaemia responds to replacement), sodium and an ECG.

Recognise that his "heart failure" may itself be the hypothyroidism. The symptoms of hypothyroidism in old age are atypical and include memory loss, lethargy, constipation, cold intolerance, fatigue, congestive heart failure, depression and weight gain — all of them often attributed to old age or other causes rather than to decreased thyroid function. Hypothyroidism causes bradycardia, reduced cardiac output, diastolic hypertension, pericardial effusion and non-pitting myxoedematous oedema that mimics cardiac failure. Reassess the cardiac diagnosis after he becomes euthyroid — his diuretic dose may need reduction.

Treatment — start low and go slow, because he has cardiac disease. Therapy should be started at 0.025 to 0.05 mg (25–50 µg) of levothyroxine per day and increased by the same increment at 1- to 3-week intervals. Given established cardiac disease, start at 12.5–25 µg daily. The rationale is that thyroid hormone increases myocardial oxygen demand and can precipitate angina, atrial fibrillation, acute coronary syndrome or worsening failure. The decreased metabolic clearance rate of thyroid hormone in ageing may lead to a lower maintenance dose of T4, and the replacement dose in older people is usually lower than in younger people.

Titration and monitoring. Increase the dose slowly, every six to eight weeks, guided by TSH — a shorter interval simply measures a level that has not yet equilibrated. Monitor heart rate, symptoms of angina, weight, bowel habit and mental state at each visit, and the TSH level in the laboratory. When indicated for symptomatic cardiovascular disease, a beta blocker may be added to the levothyroxine regimen. Aim for a TSH in the reference range but at the higher end — around 4–6 mU/L is acceptable in a 70-year-old with heart disease; avoid a suppressed TSH, which risks atrial fibrillation and bone loss.

Follow-up schedule. Review clinically and with TSH every 6–8 weeks during titration; once stable, check TSH at 6 months and then annually. Recheck earlier if there is a change in weight, a new drug that alters absorption or metabolism, an intercurrent illness, or new symptoms. At every review, reassess the heart failure medication, since diuretic and rate-control requirements often fall as he becomes euthyroid, and screen for over-replacement — palpitations, tremor, weight loss, insomnia, angina, atrial fibrillation.

Specific instructions to give this patient. (i) Take levothyroxine once daily on an empty stomach, 30–60 minutes before breakfast, with water — or at bedtime, at least two hours after food, if that is easier to remember. (ii) Separate it by at least four hours from calcium, iron, antacids, proton-pump inhibitors, sucralfate and soya products, which impair absorption — an important point in an older patient on multiple drugs. (iii) Do not stop or alter the dose yourself, and do not double up a missed dose; take it the next day. (iv) Treatment is lifelong. (v) Report immediately chest pain, palpitations, breathlessness or an irregular pulse. (vi) Expect gradual improvement over weeks to months, not days — constipation and cold intolerance settle first, weight last. (vii) Tell every doctor and pharmacist that you take levothyroxine, and stay on the same brand where possible. (viii) Continue a high-fibre diet, fluids and activity for the constipation while replacement takes effect.

Current practice has moved further towards individualised, age-adjusted TSH targets and away from combination therapy. Three points are worth stating. (a) An age-specific upper TSH reference limit is now widely accepted, since TSH rises physiologically with age; targeting the young adult range in a 70-year-old with heart disease produces over-treatment, and registry data link a suppressed TSH on levothyroxine to atrial fibrillation, osteoporotic fracture and increased mortality in older adults — so the target here is the upper half of the reference range. (b) Liothyronine (T3) and combination T4/T3 therapy are not recommended for routine use, and are specifically inadvisable in older patients with cardiac disease because of the sharp, non-physiological T3 peaks. (c) If he is on amiodarone, the guidance is that amiodarone-induced hypothyroidism does not usually require stopping the amiodarone — treat with levothyroxine and continue the antiarrhythmic if it is needed, monitoring thyroid function every 6 months for as long as he takes it and for a year afterwards.