Expansion
Block synthesis, block release, block conversion, block effects, and support
Expansion
A five-point framework, each targeting a different step:
- Block synthesis: propylthiouracil (preferred over carbimazole here) inhibits thyroid peroxidase
- Block release: iodine (Lugol’s solution or potassium iodide) via the Wolff-Chaikoff effect. Must be given at least an hour after the thionamide
- Block peripheral conversion of T4 to T3: propylthiouracil, propranolol, corticosteroids
- Block the effects: propranolol for the adrenergic features; steroids also cover relative adrenal insufficiency
- Supportive: cooling, fluids, treat the precipitant
Precipitants: infection, surgery, trauma, iodinated contrast, amiodarone, radioiodine, labour, and abrupt withdrawal of antithyroid drugs.
Features are an exaggeration of thyrotoxicosis with decompensation: fever, tachycardia or atrial fibrillation, heart failure, agitation or delirium, vomiting and diarrhoea.
Mortality remains substantial, and it is a clinical diagnosis: thyroid function tests are no more abnormal than in uncomplicated thyrotoxicosis, so treatment must not await them.