Synopsis
Detect and phenotype thyroid dysfunction caused by amiodarone or lithium, coordinate essential-drug decisions and treat hypo- or hyperthyroidism without causing cardiac or psychiatric harm.
- Check thyroid function before amiodarone, every six months during treatment and for several months after discontinuation, as MHRA advises; its long tissue half-life makes late effects biologically plausible.
- Amiodarone can cause hypothyroidism or thyrotoxicosis. High iodine exposure and inhibition of T4-to-T3 conversion also produce predictable early laboratory changes that are not automatically disease.
- Type 1 amiodarone-induced thyrotoxicosis reflects increased synthesis, often in Graves' or nodular thyroid disease; type 2 is destructive thyroiditis. Mixed or indeterminate forms are common in practice.
- A normal or modest free T3 does not safely exclude amiodarone-associated thyrotoxicosis because conversion is inhibited and severe cardiac disease may blunt classical symptoms.
- Stopping amiodarone is not a reflex endocrine decision: benefit may persist after withdrawal and arrhythmia control may be life-saving. Cardiology and endocrinology should agree the risk balance.
- Lithium commonly causes goitre or hypothyroidism and can less commonly cause thyrotoxicosis. Hypothyroidism can often be treated with levothyroxine without withdrawing an effective mood stabiliser.
- NICE recommends thyroid function, renal function and calcium monitoring at least every six months during long-term lithium treatment, with more frequent review when results change or risk is greater.
- Symptoms overlap: fatigue, weight change, tremor, anxiety, bradycardia and cognitive slowing may arise from thyroid disease, the underlying cardiac/psychiatric illness or medicine toxicity. Use biochemistry and trajectory.
- Lithium-associated hypercalcaemia or hyperparathyroidism is not thyroid dysfunction but belongs in the same safety review and can contribute to neuropsychiatric and renal symptoms.
Key red flags
Underlying nodular goitre or Graves' disease, thyroid vascularity and positive relevant antibodies can support iodine-driven increased synthesis. The distinction is probabilistic and may not be clean.
A previously normal gland, low vascularity and destructive release favour type 2 amiodarone-induced thyrotoxicosis. Inflammatory markers alone are insufficiently specific to make the diagnosis.
Dyspnoea, cough, jaundice, visual change or neuropathy on amiodarone, and diarrhoea, vomiting, coarse tremor, ataxia, confusion or renal decline on lithium, require broader urgent toxicity assessment.
Investigation priorities
Confirm persistent dysfunction and characterise its biochemical direction and severity.
Management branches
Persistent overt biochemical hypothyroidism during or after amiodarone exposure.
- Confirm persistence, symptoms and baseline pattern; check adrenal risk if severe central features are possible and review all amiodarone toxicities.
- Discuss amiodarone indication with cardiology. It can often continue while levothyroxine is introduced cautiously, especially in ischaemic or arrhythmic heart disease.
- Titrate against TSH and free T4 with clinical cardiac review, accepting that amiodarone alters peripheral conversion and that abrupt over-replacement may provoke arrhythmia.