Hyperthyroidism
Hyperthyroidism is a biochemical diagnosis caused by pathological overproduction and secretion of thyroid hormones by the thyroid gland. Thyrotoxicosis describes the clinical syndrome produced by excess circulating thyroid hormone from any cause (including destructive thyroiditis or exogenous hormone).
Distinguishing the biochemical pattern, underlying mechanism and acuity of presentation is essential in the ED because priorities differ between stable thyrotoxicosis and life‑threatening thyroid storm (NICE NG145).
Classification
- Primary hyperthyroidism: thyroid gland disease (Graves' disease, toxic multinodular goitre, toxic adenoma). Biochemistry: low TSH with raised free T4 and/or free T3.
- Overt: low TSH and elevated free T4 and/or free T3.
- Subclinical: low TSH with normal free T4 and free T3.
- Secondary hyperthyroidism: excessive TSH stimulation (rare; e.g., TSH‑secreting pituitary adenoma or assay interference).
- T3‑toxicosis: suppressed TSH with normal free T4 but raised free T3 (≈5% of cases). Request free T3 when clinical suspicion persists despite normal free T4.
Common causes
- Graves' disease (TSH‑receptor stimulating antibodies; may have orbitopathy)
- Toxic multinodular goitre
- Toxic adenoma
- Subacute or silent thyroiditis (destructive release of preformed hormone)
- Exogenous thyroid hormone excess (iatrogenic/overreplacement)
- Drug‑associated thyrotoxicosis (e.g., amiodarone)