About This Page
This is a clinician-written, evidence-based guide aligned to the MCC Examination Objectives. It is structured by clinical presentation — the way the MCCQE tests and the way patients actually present. Management reflects current Canadian guidelines (CMA, CFPC, CPS). Always cross-reference with institutional protocols and clinical judgment.
Key points
- Low TSH is the screening clue; free T4 and T3 determine biochemical severity
- Differentiate hormone overproduction from thyroiditis or exogenous thyroid hormone because treatment differs
- Thyroid storm is a clinical emergency: fever, delirium, tachyarrhythmia, heart failure, GI symptoms, and precipitating illness
- Beta-blockers relieve adrenergic symptoms; antithyroid drugs treat synthesis in Graves or toxic nodular disease
- New atrial fibrillation, osteoporosis, pregnancy, and older age change urgency and management
Approach to the Presentation
Hyperthyroidism is often tested as a symptom cluster rather than a labelled diagnosis: weight loss with appetite, palpitations, tremor, heat intolerance, sweating, anxiety, insomnia, proximal weakness, menstrual change, and diarrhoea. The first decision is whether the patient is unstable or has thyroid storm. Then determine whether this is Graves disease, toxic nodular disease, thyroiditis, medication exposure, iodine/amiodarone effect, or factitious thyroid hormone. Canadian practice generally starts with TSH, free T4, and free T3; TSH receptor antibodies and radionuclide uptake scanning help define cause when the clinical picture is not obvious.
Differential Diagnosis
| diagnosis | likelihood | key features | distinguishing test |
|---|---|---|---|
| Thyroid Storm | must-not-miss | Fever, severe tachycardia, AF, heart failure, delirium, agitation, vomiting, diarrhoea, jaundice, precipitated by infection, surgery, trauma, childbirth, or iodine load | Clinical diagnosis supported by suppressed TSH and high free T4/T3; do not wait for labs if critically ill |
| Atrial Fibrillation with Rapid Ventricular Response | must-not-miss | Palpitations, dyspnea, chest discomfort, syncope or heart failure in thyrotoxic patient, especially older adult | ECG showing AF; TSH suppressed and free T4/T3 elevated |
| Graves Disease | common | Diffuse goitre, bruit, ophthalmopathy, pretibial myxoedema, symmetric hyperthyroid symptoms, autoimmune history | TSH receptor antibodies positive; diffuse increased uptake on radionuclide scan |
| Toxic Multinodular Goitre | common | Older patient, nodular goitre, subclinical or overt hyperthyroidism, AF or osteoporosis | Suppressed TSH; patchy increased uptake on radionuclide scan |
| Toxic Adenoma | common | Single autonomous nodule with hyperthyroidism; surrounding thyroid tissue suppressed | Suppressed TSH; focal hot nodule on radionuclide scan |
| Anxiety / Panic Disorder Mimic | common | Palpitations, tremor, sweating, insomnia without objective thyroid biochemical abnormality | Normal TSH and free T4/T3 |
| Subacute Thyroiditis | less common | Painful tender thyroid after viral illness, fever, transient thyrotoxicosis, then hypothyroid phase | High ESR/CRP; low uptake on radionuclide scan |
| Postpartum or Painless Thyroiditis | less common | Painless thyrotoxic phase after pregnancy or autoimmune thyroiditis, often followed by hypothyroidism | Low uptake; anti-TPO may be positive |
| Exogenous Thyroid Hormone Use | less common | Weight loss, palpitations, suppressed TSH without goitre; may be prescribed overtreatment or factitious | Low thyroglobulin and low uptake; medication reconciliation |
| Amiodarone- or Iodine-induced Thyrotoxicosis | less common | Exposure to amiodarone or iodinated contrast; may occur with nodular thyroid or destructive thyroiditis | TSH/free T4/T3; uptake often low after iodine exposure; specialist differentiation |
Red Flags & Key History
Symptoms
Fever, delirium, severe agitation, vomiting, diarrhoea, jaundice, or heart failure — thyroid storm
Chest pain, syncope, dyspnea, or new irregular pulse — AF, ischemia, or heart failure
Pregnancy or early postpartum state with thyrotoxicosis
Eye pain, diplopia, corneal exposure, or reduced vision in Graves ophthalmopathy
Recent amiodarone, iodine contrast, thyroid hormone, supplements, or biotin use
Weight loss despite appetite, tremor, heat intolerance, sweating, insomnia, proximal weakness
Neck pain after viral illness — subacute thyroiditis rather than Graves
Signs
Temperature elevation, severe tachycardia, hypotension, heart failure signs, or altered mental status
Irregularly irregular pulse suggesting AF
Diffuse goitre with bruit, lid lag, proptosis, or pretibial myxoedema — Graves disease
Tender thyroid — subacute thyroiditis
Proximal myopathy, hyperreflexia, fine tremor, warm moist skin
Large nodular goitre or compressive features
Approach to Investigation
First-line
TSHBest initial screening test; suppressed in primary hyperthyroidism
Free T4 and free T3Quantify severity; T3 toxicosis can occur with normal free T4
ECGAssess AF, flutter, tachyarrhythmia, ischemia, and rate-related complications
CBC, liver enzymes, electrolytes, glucoseBaseline before antithyroid drugs and to assess systemic illness or thyroid storm complications
Second-line
TSH receptor antibodiesSupports Graves disease and is useful in pregnancy because antibodies can affect fetal/neonatal thyroid status
Radionuclide uptake scanHigh diffuse uptake = Graves; focal/patchy uptake = toxic adenoma/multinodular goitre; low uptake = thyroiditis or exogenous hormone
ESR/CRPHigh in subacute thyroiditis
Thyroid ultrasoundNot routine for biochemical hyperthyroidism unless palpable nodule/goitre, suspicious nodule, or compressive symptoms
Specialist
Endocrinology referralThyroid storm, pregnancy, severe Graves ophthalmopathy, amiodarone-induced disease, uncertain cause, or definitive therapy planning
Ophthalmology referralVisual symptoms, diplopia, corneal exposure, or severe Graves orbitopathy
Management Principles
Canadian practice informed by CMAJ thyroid disease reviews and Choosing Wisely Canada endocrine recommendations1
Stabilise and identify emergencies
- If thyroid storm suspected: admit, monitor, treat precipitant, give beta-blocker, antithyroid drug, iodine after thionamide, glucocorticoid, and supportive care with specialist/ICU involvement
- Treat AF, heart failure, dehydration, fever, and infection according to acuity
- Avoid aspirin for fever in severe thyrotoxicosis because it can increase free thyroid hormone fraction
2
Symptom control
- Beta-blocker such as propranolol or atenolol for tremor, palpitations, and adrenergic symptoms unless contraindicated
- Use rate control and anticoagulation decisions for AF according to Canadian cardiovascular practice and individual stroke risk
3
Cause-specific treatment
- Graves or toxic nodular disease: methimazole is usual first-line antithyroid drug outside first trimester pregnancy; PTU is preferred in first trimester or thyroid storm
- Thyroiditis: antithyroid drugs do not help because hormone is leaking, not being overproduced; use NSAIDs or glucocorticoids for pain/inflammation and beta-blocker for symptoms
- Consider radioactive iodine or surgery for relapse, large goitre, compressive symptoms, toxic nodular disease, or patient preference
Complications & Pitfalls
- Treating thyroiditis with methimazole: Thyroiditis is destructive release of stored hormone, so antithyroid drugs are ineffective
- Missing thyroid storm: Fever and delirium in thyrotoxicosis are emergency features even before confirmatory labs return
- Ignoring AF: New atrial fibrillation may be the presenting feature in older adults
- Biotin interference: High-dose biotin can distort thyroid immunoassays and create misleading results
- Pregnancy nuance: Graves antibodies and antithyroid drug choice matter for fetal and maternal safety
MCCQE1 Exam Tips
- 1Suppressed TSH is the entry point; then order free T4/T3 to confirm and grade severity
- 2Thyroid storm is a clinical diagnosis: fever, delirium, tachyarrhythmia, GI symptoms, and precipitant
- 3Graves clues: diffuse goitre, bruit, ophthalmopathy, pretibial myxoedema, positive TSH receptor antibodies
- 4Thyroiditis has neck pain or postpartum context and low uptake; treat symptoms rather than hormone synthesis
- 5Methimazole is usual first-line outside first trimester; PTU is preferred in first trimester and thyroid storm
- 6Do not order thyroid ultrasound for biochemical hyperthyroidism without a palpable abnormality
- 7MCC stems often present older adults with AF or weight loss rather than classic textbook hyperthyroid symptoms
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