Why Thyroid Emergencies Are High-Yield
Thyroid storm and myxoedema coma are rare but high-mortality endocrine emergencies that appear disproportionately often in OSCEs precisely because they test whether you can recognise a decompensated version of a condition you already know well from routine thyroid history and examination stations. Both carry significant mortality if unrecognised, and both require empirical treatment based on clinical suspicion rather than waiting for confirmatory thyroid function tests.
⚠️ Red Flag
Neither diagnosis has a single confirmatory bedside test that returns quickly enough to guide immediate treatment. Both are clinical diagnoses supported by history and examination, treatment must start before formal TFTs return.
Thyroid Storm (Thyrotoxic Crisis)
Thyroid storm is a life-threatening exaggeration of thyrotoxicosis, usually precipitated by a stressor in a patient with untreated or undertreated hyperthyroidism.
Precipitants
🧠 Mnemonic
TRIISS for thyroid storm precipitants:
- Trauma or surgery (especially thyroid surgery or unrelated surgery in undiagnosed thyrotoxicosis)
- Radioiodine treatment (can transiently release stored hormone)
- Infection (the most common precipitant)
- Iodinated contrast administration
- Stopping antithyroid medication abruptly
- Substance, e.g. amiodarone (iodine-rich), pregnancy, or diabetic ketoacidosis co-occurring
Clinical Features
- Hyperpyrexia (often >39°C, a key discriminating feature from simple thyrotoxicosis)
- Tachycardia, often with atrial fibrillation, and can progress to heart failure
- Agitation, confusion, delirium, progressing to seizures or coma in severe cases
- GI symptoms: vomiting, diarrhoea, abdominal pain, jaundice (hepatic dysfunction from a hypermetabolic state)
- Severe tremor, sweating, and signs of the underlying cause (goitre, exophthalmos if Graves')
💎 Clinical Pearl
The Burch-Wartofsky Point Scale is used to stratify likelihood of thyroid storm, scoring temperature, CNS effects, GI/hepatic dysfunction, tachycardia, presence of atrial fibrillation, and heart failure. A score above 45 is highly suggestive; below 25 is unlikely. You are not expected to calculate this from memory in an OSCE, but knowing it exists and what it captures is often asked.
Management, Five Simultaneous Targets
🧠 Mnemonic
BBAIS for thyroid storm management, treat all simultaneously:
- Beta-blockade (IV propranolol, also reduces peripheral T4-to-T3 conversion)
- Block hormone synthesis (high-dose propylthiouracil or carbimazole)
- Administer iodine (Lugol's iodine or potassium iodide), given at least 1 hour after antithyroid drugs to prevent the iodine being used as substrate for new hormone synthesis (Wolff-Chaikoff-exploiting strategy)
- IV hydrocortisone (blocks peripheral T4-to-T3 conversion and covers possible co-existing relative adrenal insufficiency)
- Supportive care (cooling for hyperpyrexia, IV fluids, treat the precipitant, e.g. antibiotics for infection)
⚠️ Red Flag
Never give aspirin for the fever in thyroid storm. Aspirin displaces thyroid hormone from binding proteins, increasing free hormone levels and worsening the crisis. Use paracetamol and physical cooling measures instead.
Myxoedema Coma (Severe Hypothyroidism)
The decompensated opposite extreme, a rare, life-threatening presentation of severe, prolonged untreated hypothyroidism, again usually precipitated by a stressor.
Precipitants
- Infection (most common)
- Cold exposure
- Sedative or opioid medication (reduced clearance in hypothyroidism)
- Stopping thyroxine replacement, myocardial infarction, stroke, trauma
Clinical Features
🧠 Mnemonic
COLD-HH for myxoedema coma:
- Confusion, reduced consciousness, or coma
- Oedema (non-pitting, periorbital)
- Low temperature (hypothermia, often profound and a key discriminator)
- Decreased reflexes (slow-relaxing "hung-up" reflexes)
- Hypoventilation (CO2 retention, respiratory failure)
- Hypotension and bradycardia
Also look for hyponatraemia (common, due to impaired free water excretion) and hypoglycaemia.
Management
- IV levothyroxine (T4) and/or liothyronine (T3) loading dose, followed by daily maintenance, given IV as GI absorption cannot be relied upon in a comatose patient
- IV hydrocortisone before or alongside thyroid hormone replacement, essential because thyroid hormone replacement can precipitate an adrenal crisis if co-existing (often unrecognised) adrenal insufficiency is not covered first
- Passive rewarming (active rapid rewarming can cause vasodilation and cardiovascular collapse)
- Supportive care: ventilatory support if hypoventilating, cautious fluid management, treat the precipitant (e.g. antibiotics), correct hypoglycaemia
💎 Clinical Pearl
Why give hydrocortisone before/with thyroxine in myxoedema coma? Hypothyroidism and adrenal insufficiency can co-exist (e.g. in autoimmune polyglandular syndromes, or secondary hypothyroidism from pituitary failure that also affects ACTH). Thyroid hormone replacement increases metabolic rate and cortisol clearance; giving thyroxine without covering for possible adrenal insufficiency first can precipitate an adrenal crisis. This exact same principle, treat possible adrenal insufficiency alongside or before the primary emergency, appears across multiple endocrine emergency stations.
Comparing the Two Emergencies
| Feature | Thyroid storm | Myxoedema coma |
|---|---|---|
| Temperature | Hyperpyrexia | Hypothermia |
| Heart rate | Tachycardia, often AF | Bradycardia |
| Mental state | Agitation, delirium | Confusion, coma |
| Key drug | Propranolol, antithyroid drugs, iodine | IV levothyroxine/liothyronine |
| Shared step | IV hydrocortisone in both | IV hydrocortisone in both |
| Mortality | Significant if untreated | Very high (up to 30-40%) if untreated |
Red Flags, Never Miss
⚠️ Red Flag
- Hyperpyrexia with tachycardia and delirium in a patient with a goitre or known Graves' disease, treat empirically as thyroid storm
- Profound hypothermia with bradycardia and confusion in an elderly patient, especially found collapsed at home in winter, consider myxoedema coma
- Do not wait for TFT results in either scenario if clinical suspicion is high; both require immediate empirical treatment
Frequently Asked Questions
"Why must iodine be given after, not before, antithyroid drugs in thyroid storm?"
If iodine is given before the antithyroid drug (propylthiouracil or carbimazole) has blocked new hormone synthesis, the excess iodine can act as substrate and paradoxically fuel further thyroid hormone production (the Jod-Basedow effect), worsening the crisis. Giving the antithyroid drug at least an hour first ensures the gland cannot use the iodine load to make more hormone.
"Why is propranolol preferred over other beta-blockers in thyroid storm?"
Propranolol, at high doses, has the additional benefit of inhibiting peripheral conversion of T4 to the more biologically active T3, on top of its beta-blocking effect on tachycardia and tremor, making it particularly suited to this specific emergency.
"What is the mortality of untreated myxoedema coma, and why is it so high?"
Untreated, mortality approaches 30-40%, driven by cardiovascular collapse, respiratory failure from hypoventilation, and complications of the underlying precipitant. Even with treatment, mortality remains significant, which is why early recognition and immediate empirical treatment are so heavily emphasised.