Free exam prep

AMC CAT MCQ Examination (AMC Part 1)

Thyroid disease assessment

Q: A 29-year-old woman with a three-month history of heat intolerance, palpitations, weight loss, and bilateral eye irritation is diagnosed with Graves' disease based on an elevated free T4 and high TSH-receptor antibody titre. She is commenced on oral carbimazole 20 mg once daily and propranolol 20 mg three times daily. She is reviewed four weeks later and reports that her palpitations have resolved. What critical advice regarding medication adverse effects must be emphasized to this patient?

Stop carbimazole immediately and obtain an urgent full blood count if fever, mouth ulcers, or a sore throat develops. Carbimazole is the first-line antithyroid drug in Australia. Its most feared and life-threatening adverse effect is agranulocytosis (absolute neutrophil count below 0.5 x 10^9/L), which occurs idiosyncratically in 0.2% to 0.5% of treated patients. Clinical guidelines mandate that every patient commencing a thionamide must receive both verbal and written warnings: if they develop any symptoms of infection—such as a sore throat, fever, mouth ulcers, or unexplained rigors—they must immediately stop taking the medication and obtain an urgent full blood count. Continuing carbimazole during agranulocytosis can lead to overwhelming, fatal sepsis. Dietary calcium restriction is inappropriate; patients with thyrotoxicosis are actually at increased risk of osteopenia. Mild skin dryness or hair thinning does not warrant abrupt cessation of antithyroid therapy. Worsening orbitopathy requires specialist ophthalmological assessment and glucocorticoids or radioiodine precautions, not doubling of antithyroid doses.

Q: A 34-year-old woman presents to her general practitioner with a two-week history of fatigue, nervousness, heat intolerance, and severe anterior neck pain that radiates to her left ear and jaw. She reports having a mild upper respiratory tract viral infection three weeks ago. On physical examination, her temperature is 37.9 C, pulse is 104 bpm, and blood pressure is 128/78 mmHg. Palpation of the anterior neck reveals an exquisitely tender, diffusely enlarged, firm thyroid gland. Laboratory investigations reveal: TSH < 0.02 mIU/L (normal 0.4 - 4.0), free T4 28.4 pmol/L (normal 10 - 20), erythrocyte sedimentation rate (ESR) 92 mm/h (normal < 20), and negative TSH-receptor antibodies. A diagnostic radionuclide pertechnetate scan reveals negligible thyroid tracer uptake (0.4%). What is the most appropriate management plan for this patient?

Prescribe oral non-steroidal anti-inflammatory drugs or oral prednisolone alongside propranolol for symptom relief. This clinical picture is classic for subacute granulomatous thyroiditis (de Quervain's thyroiditis), a post-viral inflammatory disorder of the thyroid gland. Hallmark features include exquisite anterior neck tenderness radiating to the ears/jaw, systemic symptoms (fever, malaise), a marked elevation in inflammatory markers (ESR characteristically above 50 to 90 mm/h), transient hyperthyroidism driven by follicular destruction and leak of stored preformed thyroid hormone, and absent or negligible radionuclide uptake. Because the thyrotoxicosis results from follicular leakage rather than increased de novo hormone synthesis, antithyroid medications such as carbimazole and propylthiouracil are completely ineffective and contraindicated. Radioactive iodine and surgical thyroidectomy are also inappropriate for a self-limiting condition. Treatment is symptomatic: high-dose NSAIDs (e.g. ibuprofen or naproxen) or a short course of oral prednisolone (e.g. 25 to 50 mg daily tapered over several weeks) to alleviate pain and glandular inflammation, alongside a non-selective beta-blocker (propranolol) to control adrenergic manifestations.

Key Takeaways

A suppressed TSH requires interpretation with free T4 and T3.
Thyroiditis does not usually benefit from antithyroid synthesis-blocking drugs.
Mild subclinical hypothyroidism does not automatically require levothyroxine.

Last updated: October 2026

Thyroid Disorders, Adrenal Insufficiency & Cushing Syndrome

Endocrine disorders involving the hypothalamic-pituitary-thyroid and hypothalamic-pituitary-adrenal axes represent high-yield clinical domains in adult internal medicine. Subtle clinical presentations often mimic psychiatric or general functional complaints, yet delayed recognition of acute crises—such as thyroid storm, myxoedema coma, or acute adrenal crisis—carries substantial mortality.

Thyroid Function Test (TFT) Interpretation

Serum thyroid-stimulating hormone (TSH) secreted by the anterior pituitary is the most sensitive screening biomarker of thyroid status, exhibiting an inverse log-linear relationship with circulating free thyroxine (FT4).

Biochemical Patterns of Thyroid Disease

Primary Hypothyroidism: Serum TSH: Elevated ( $> 4.0\text{ mIU/L}$ ); Free T4 (FT4): Low ( $< 10\text{ pmol/L}$ ); Free T3 (FT3): Low or Normal; Diagnostic Implications & Next Steps: Autoimmune thyroiditis (Hashimoto's) in $> 90\%$ . Check anti-TPO antibodies. Treat with oral levothyroxine.
Subclinical hypothyroidism: Elevated TSH with normal free T4; the TSH need not remain below 10. Interpret against the laboratory range and repeat when appropriate. Treatment depends on persistent degree of elevation, symptoms, pregnancy and individual risk, rather than requiring treatment for every mild elevation.
Central (Secondary) Hypothyroidism: Serum TSH: Low or Inappropriately Normal; Free T4 (FT4): Low; Free T3 (FT3): Low; Diagnostic Implications & Next Steps: Pituitary adenoma, apoplexy, Sheehan syndrome, craniopharyngioma. Rule out adrenal insufficiency before starting thyroxine.
Primary Hyperthyroidism: Serum TSH: Suppressed ( $< 0.05\text{ mIU/L}$ ); Free T4 (FT4): Elevated; Free T3 (FT3): Elevated; Diagnostic Implications & Next Steps: Graves' disease, toxic multinodular goitre, toxic adenoma. Check TRAb and radionuclide thyroid uptake scan.
Subclinical Hyperthyroidism: Serum TSH: Suppressed ( $< 0.1\text{ mIU/L}$ ); Free T4 (FT4): Normal; Free T3 (FT3): Normal; Diagnostic Implications & Next Steps: Increased risk of atrial fibrillation and osteoporosis in postmenopausal women and elderly; monitor or treat if $\text{TSH} < 0.1\text{ mIU/L}$ .
TSH-Secreting Pituitary Adenoma: Serum TSH: Elevated or Normal; Free T4 (FT4): Elevated; Free T3 (FT3): Elevated; Diagnostic Implications & Next Steps: Rare; pituitary MRI shows sellar lesion; alpha-subunit elevated; distinguished from thyroid hormone resistance.
Non-Thyroidal Illness (Euthyroid Sick): Serum TSH: Low, Normal, or High; Free T4 (FT4): Normal or Low; Free T3 (FT3): Low; Diagnostic Implications & Next Steps: Severe acute illness/sepsis down-regulates deiodinases; elevated reverse T3 (rT3); do not treat with thyroxine; recheck post-recovery.

Pitfall in Central Hypothyroidism: Commencing levothyroxine monotherapy in a patient with unrecognised hypopituitarism without first evaluating and replacing cortisol can precipitate a fatal acute adrenal crisis, because thyroxine accelerates metabolic clearance of cortisol.

Hyperthyroidism & Thyrotoxicosis

Thyrotoxicosis describes the clinical state of excessive circulating thyroid hormone, whereas hyperthyroidism refers specifically to de novo thyroid gland hypersecretion.

Differential Diagnosis of Thyrotoxicosis

Clinical Entities

Graves' Disease:
- Aetiology: Autoimmune disorder caused by circulating immunoglobulin G antibodies targeting the TSH receptor (TRAb / TSI), stimulating continuous hormone synthesis and thyroid growth.
- Extrathyroidal Hallmarks:
  - Graves' Orbitopathy (Ophthalmopathy): Proptosis, chemosis, periorbital oedema, and diplopia driven by TSH-receptor activation on retro-orbital fibroblasts with glycosaminoglycan accumulation. Worsened by smoking.
  - Pretibial Myxoedema (Thyroid Dermopathy): Non-pitting, violaceous, indurated orange-peel (peau d'orange) plaques over the anterior shins.
  - Thyroid Acropachy: Digital clubbing and periosteal new bone formation.
- First-Line Pharmacotherapy:
  - Carbimazole (converted in vivo to methimazole): Standard first-line agent in Australia. Starting dose $15 - 40\text{ mg}$ orally once daily, titrated as TFTs normalize.
  - Propylthiouracil (PTU): Preferred in the first trimester of pregnancy (due to carbimazole embryopathy: choanal atresia, aplasia cutis) and in thyroid storm (inhibits peripheral conversion of T4 to T3). In non-pregnant adults, carbimazole is preferred due to PTU-induced severe fulminant hepatotoxicity.
- The Agranulocytosis Emergency:
  - Occurs in $0.2 - 0.5\%$ of patients on thionamides (carbimazole or PTU), typically within the first 3 months.
  - Absolute neutrophil count drops below $0.5 \times 10^9\text{/L}$ .
  - Mandatory Patient Education: Patients must be explicitly instructed: If you develop a sore throat, fever, mouth ulcers, or any signs of systemic infection, stop carbimazole immediately and attend an emergency department or general practitioner for an urgent full blood count. Never wait for a routine clinic appointment.
- Radioactive Iodine ( $^{131}\text{I}$ ) & Surgery:
  - Radioiodine is definitive therapy for relapse; contraindicated in pregnancy, breastfeeding, and active moderate-to-severe Graves' orbitopathy (may trigger flare of eye disease; requires oral prednisolone prophylaxis).
  - Total thyroidectomy is indicated for large compressive goitres, suspected malignancy, or co-existing severe active orbitopathy.
Toxic Multinodular Goitre (MNG) & Toxic Adenoma:
- Autonomous monoclonal somatic mutations in the TSH receptor gene leading to constitutive activation without autoimmune antibodies (TRAb negative).
- Scintigraphy demonstrates patchy uptake in multiple nodules or a single hyperfunctioning 'hot' nodule with suppression of the surrounding gland.
- Medical therapy rarely induces permanent remission; definitive therapy requires radioactive iodine or surgery.
Thyroiditis Syndromes:
- Subacute Granulomatous (de Quervain's) Thyroiditis: Post-viral inflammatory condition presenting with fever, exquisite anterior neck tenderness, pain radiating to the jaw/ears, and elevated ESR ( $> 50 - 100\text{ mm/h}$ ) and CRP. Characterized by a triphasic course: initial hyperthyroidism (follicular disruption releasing preformed hormone) lasting 2-6 weeks, followed by transient hypothyroidism, and eventual euthyroid recovery. Radionuclide uptake is negligible ( $< 1\%$ ). Treated with NSAIDs or oral prednisolone; beta-blockers for symptoms. Thionamides are completely ineffective because hormone synthesis is not increased.
- Postpartum & Painless Thyroiditis: Autoimmune lymphocytic infiltration; painless goitre, anti-TPO positive, transient thyrotoxicosis with low radioiodine uptake.

Life-Threatening Thyroid Emergencies

Primary references (checked 7 October 2026): Endocrine Society adrenal guidance.

Test Your Knowledge

A 29-year-old woman with a three-month history of heat intolerance, palpitations, weight loss, and bilateral eye irritation is diagnosed with Graves' disease based on an elevated free T4 and high TSH-receptor antibody titre. She is commenced on oral carbimazole 20 mg once daily and propranolol 20 mg three times daily. She is reviewed four weeks later and reports that her palpitations have resolved. What critical advice regarding medication adverse effects must be emphasized to this patient?

Stop carbimazole immediately and obtain an urgent full blood count if fever, mouth ulcers, or a sore throat develops

Maintain strict dietary calcium restriction to prevent rapid bone demineralization and hypercalcaemia

Discontinue therapy and report to the clinic if she develops mild hair thinning or skin dryness over the shins

Double the carbimazole dose immediately if eye redness or double vision worsens over the coming month

Test Your Knowledge

A 34-year-old woman presents to her general practitioner with a two-week history of fatigue, nervousness, heat intolerance, and severe anterior neck pain that radiates to her left ear and jaw. She reports having a mild upper respiratory tract viral infection three weeks ago. On physical examination, her temperature is 37.9 C, pulse is 104 bpm, and blood pressure is 128/78 mmHg. Palpation of the anterior neck reveals an exquisitely tender, diffusely enlarged, firm thyroid gland. Laboratory investigations reveal: TSH < 0.02 mIU/L (normal 0.4 - 4.0), free T4 28.4 pmol/L (normal 10 - 20), erythrocyte sedimentation rate (ESR) 92 mm/h (normal < 20), and negative TSH-receptor antibodies. A diagnostic radionuclide pertechnetate scan reveals negligible thyroid tracer uptake (0.4%). What is the most appropriate management plan for this patient?

Commence oral carbimazole 30 mg daily and refer to an endocrine surgeon for urgent total thyroidectomy

Prescribe oral non-steroidal anti-inflammatory drugs or oral prednisolone alongside propranolol for symptom relief

Administer oral propylthiouracil 100 mg three times daily and prepare the patient for radioactive iodine ablation

Initiate broad-spectrum intravenous flucloxacillin and arrange an urgent ultrasound-guided needle aspiration

Sections you finish are checked off in the contents.

Up Next

Thyroid emergencies and adrenal disease

Continue learning