Treatment of Hypothyroidism

Hypothyroidism is deficient thyroid hormone action. In old age the commonest cause is autoimmune (Hashimoto's) thyroiditis, followed by earlier thyroid surgery or radioiodine given for thyrotoxicosis.

The three aims of treatment are: relieve symptoms and signs, normalise TSH to an age-appropriate range, and avoid over-treatment.

Presentation in the elderly is atypical — memory loss, lethargy, constipation, cold intolerance, fatigue, heart failure, depression, weight gain. Absence of these symptoms does not rule out hypothyroidism, so a high index of suspicion is needed.

Levothyroxine (LT4) sodium, orally, once daily, on an empty stomach 30–60 minutes before breakfast.

Separate by at least 4 hours from calcium, iron, proton pump inhibitors, soya, bile acid sequestrants, which impair absorption.

The full replacement dose in young adults is 1.6 µg/kg/day. In older people the requirement is lower — because of reduced lean body mass and the physiological age-related fall in T4 production.

Start very low: 12.5–50 µg/day, particularly if there is coronary artery disease, arrhythmia or multiple cardiac risk factors.

Increase slowly, every 6–8 weeks, aiming to reach the replacement dose only after 4–6 months.

Thyroid hormone increases myocardial oxygen consumption — rapid replacement can precipitate angina, myocardial infarction or cardiac arrhythmia.

In heart failure or established rhythm disturbance, a deliberately sub-replacement dose may be the correct choice to prevent ischaemic symptoms.

In older patients there is a narrow window between TSH suppression and the substitution dose, due to increased thyrotroph sensitivity to negative feedback by T4.

The TSH target is shifted upward with age: approximately 4–6 mIU/L at 70–80 years and 6–7 mIU/L above 80 years, especially where there is risk of arrhythmia or fragility fracture.

Check TSH every 3 months during titration; once stable, once or twice yearly with small dose adjustments.

Central (secondary) hypothyroidism — titrate to free T4 in the upper half of the normal range, never to TSH. The European Thyroid Association has issued 34 recommendations for this uncommon but difficult condition.

Myxoedema coma — IV levothyroxine (± liothyronine), IV hydrocortisone until adrenal insufficiency is excluded, passive rewarming, ventilatory and fluid support, and treatment of the precipitant.

Non-thyroidal illness — do not start levothyroxine on abnormal tests during acute illness; recheck after recovery. Treat only if there is real evidence of hypothyroidism (for example TSH >20 mIU/L with low free T4, or clear history and signs).

Over-replacement causes iatrogenic thyrotoxicosis → atrial fibrillation, osteoporosis and fragility fracture, anxiety, muscle wasting, insomnia.

Warn the patient and caregiver to report new angina, breathlessness, confusion or insomnia.

Many older patients began levothyroxine when younger for inappropriate or transient indications and continue without review. In one nursing-home study, thyroid hormone was successfully withdrawn in half the residents — always re-examine the indication.

Poor adherence is the commonest cause of a persistently raised TSH despite an apparently adequate dose.