Hypothyroidism

Hypothyroidism is a common endocrine disorder resulting from deficient thyroid hormone production. It presents on a clinical spectrum ranging from asymptomatic to severe manifestations such as myxoedema coma. Primary hypothyroidism, accounting for >99% of cases, typically results from autoimmune thyroiditis (e.g. Hashimoto's thyroiditis) or iatrogenic causes. Central and extrathyroidal forms are rare. Diagnosis primarily relies on elevated serum thyroid-stimulating hormone (TSH) concentrations and reduced free thyroxine (FT4) concentrations. Levothyroxine remains the cornerstone of treatment, aiming to return TSH concentrations to normal and alleviate symptoms. However, a proportion of patients remain symptomatic despite biochemical correction, leading to continuing debate about alternative therapies including liothyronine or desiccated thyroid extract. Subclinical hypothyroidism, with elevated TSH and normal FT4 concentrations, poses a treatment dilemma, although therapy is often considered in younger individuals, those with symptoms or women planning pregnancy. Key management principles include dose individualization, awareness of drug interactions and the importance of the correct timing of administration to optimize absorption. Special considerations apply to populations such as pregnant women, elderly individuals and patients with myxoedema coma. Updated guidance supports a tailored approach to diagnosis and treatment to prevent both under- and overtreatment.