Toxic Multinodular Goitre (TMNG) - General Surgery Notes (BDS 3rd Year)

Definition

• S Das Manual on Clinical Surgery, 13th Ed.: "Toxicity is superimposed on a previously diseased gland, more commonly a nodular goitre."

Epidemiology / Incidence

Aetiology / Pathogenesis

1. Autonomous nodule formation - specific nodules undergo genetic change leading to clonal expansion and autonomous thyroid hormone production independent of TSH control
2. Jod-Basedow effect - exposure to large doses of iodine (e.g., iodinated contrast media, amiodarone) can precipitate hyperthyroidism, especially in iodine-deficient areas
3. In some cases, the nodules themselves are inactive and it is the internodular thyroid tissue that is overactive
4. In others, one or more nodules are autonomously overactive (behaving like toxic adenomas)

Difference: Primary vs. Secondary Toxic Goitre

Clinical Features

Symptoms

1. Long-standing goitre - lump in the neck for many years before toxicity
2. Cardiovascular symptoms (predominant):
   • Palpitations
   • Atrial fibrillation (AF) - irregular pulse
   • Precordial pain and exhaustion
   • Heart failure (late)
3. Compressive symptoms (from the MNG itself):
   • Dysphagia (difficulty swallowing solids)
   • Dyspnoea (especially at night)
   • Stridor (if large)
   • Engorgement of neck veins
4. General thyrotoxic symptoms (milder than Graves'):
   • Weight loss, heat intolerance, sweating
   • Weakness, fatigue

Signs

• Asymmetrically enlarged thyroid with nodular surface
• Nodules of varying consistency (soft to hard)
• Moves on swallowing
• Irregular pulse (AF)
• No exophthalmos (distinguishing from Graves')
• No tongue tremor (distinguishing from Graves')
• Degree of thyroid hyperfunction is less marked than Graves' disease

Investigations

1. Thyroid Function Tests (TFTs)

• Serum TSH - suppressed (low / undetectable)
• Serum T3 and T4 - elevated
• Combination of toxicity + nodularity → indication for isotope scan

2. Isotope Scan (Radioiodine / Tc-99m scan)

• Investigation of choice when toxicity is associated with nodularity
• Shows "hot" (autonomously functioning) nodules with suppression of surrounding normal tissue
• Localises the area(s) of hyperfunction

3. Ultrasonography (USG)

• First-line investigation for thyroid nodules
• Determines physical characteristics (solid, cystic, mixed)
• Features suggesting malignancy: microcalcification, increased vascularity, capsular breach, nodal involvement

4. FNAC (Fine Needle Aspiration Cytology)

• For nodules not clearly benign on USG
• Ideally under USG guidance
• Cannot distinguish benign follicular adenoma from follicular carcinoma (needs histology)

5. Other

• Chest X-ray / CT scan: tracheal deviation, compression, retrosternal extension
• ECG: AF, tachyarrhythmias
• Autoantibody titres: TSH receptor antibodies (usually absent in TMNG, unlike Graves')

Treatment

1. Medical (Antithyroid Drugs) - Temporary / Pre-operative

• Carbimazole or Propylthiouracil (PTU) - used to render the patient euthyroid before surgery or radioiodine
• Important: These drugs cannot cure TMNG. The overactive tissue is autonomous, and hyperthyroidism recurs when drugs are stopped
• Useful: smaller starting doses than Graves' (biochemically less severe)
• If surgery/radioiodine not possible - thionamides can be continued long-term

• Beta-blockers (Propranolol) - promptly controls palpitations, tremor, tachycardia; higher doses may be needed due to accelerated drug clearance in thyrotoxicosis
• Anticoagulation (Warfarin / NOAC) - if AF is present, to prevent thromboembolism

2. Radioiodine (¹³¹I) - Definitive Treatment of Choice

• First-line definitive treatment for most TMNG patients (especially elderly)
• Patient must first be rendered euthyroid with antithyroid drugs, then drugs stopped 3-7 days before treatment
• Destroys the overactive thyroid tissue
• May need repeat doses
• Results in hypothyroidism over time - requires lifelong thyroxine replacement

3. Surgery - Subtotal / Total Thyroidectomy

• Large compressive goitre with pressure symptoms (dyspnoea, dysphagia)
• Suspected malignancy
• Retrosternal/intrathoracic extension
• Cosmetic reasons / patient preference
• Failure of or contraindication to radioiodine

• Subtotal thyroidectomy - reduces mass of overactive tissue below a critical level; risk of recurrence (~5%) and late hypothyroidism
• Total/Near-total thyroidectomy - eliminates recurrence risk; accepts immediate hypothyroidism requiring lifelong T4 replacement

• Render patient euthyroid with antithyroid drugs (Carbimazole/PTU) for 6-8 weeks
• Lugol's iodine for 10 days before surgery (reduces vascularity)
• Beta-blockers

• Recurrence of thyrotoxicosis (~5% with subtotal thyroidectomy)
• Permanent hypoparathyroidism (hypocalcaemia) - injury to parathyroid glands
• Recurrent laryngeal nerve injury - hoarseness
• Hypothyroidism
• Cosmetic scar in young women
• Reactionary/secondary haemorrhage

Complications of Untreated TMNG

1. Atrial fibrillation
2. Heart failure (thyrotoxic cardiomyopathy)
3. Tracheal compression (dyspnoea, stridor)
4. Haemorrhage into nodule (sudden painful enlargement)
5. Malignant transformation (~4% risk in nodular goitre)
6. Thyroid storm (rare in TMNG, more in Graves')

Histopathology

• Cut surface shows nodules with haemorrhagic and necrotic areas separated by normal thyroid tissue
• Nodules vary from hyperactive (hot) to inactive (cold) to calcified
• Active follicles lined by tall columnar epithelium (hyperplasia)
• Vacuolated colloid with scalloped pattern adjacent to thyrocytes

Key Exam Points (Summary)

1. TMNG = secondary toxic goitre (toxicity on pre-existing nodular goitre)
2. Age: elderly; no exophthalmos; cardiovascular symptoms predominate
3. Degree of thyroid hyperfunction is LESS than Graves'
4. Pulse is irregular (AF) - not simply tachycardic
5. Isotope scan = investigation of choice (shows hot nodules)
6. Antithyroid drugs = cannot cure; used for preparation
7. Definitive treatment: radioiodine OR surgery (total/subtotal thyroidectomy)
8. Jod-Basedow effect = iodine-induced hyperthyroidism in endemic areas
9. Most common cause of hyperthyroidism in the elderly in iodine-replete regions

🎯 Framed 10-Mark Question (BDS 3rd Year - General Surgery Style)

Q. Define toxic multinodular goitre. Describe its clinical features, investigations and treatment. (10 marks)

✍️ MODEL ANSWER

TOXIC MULTINODULAR GOITRE (10 Marks)

DEFINITION (1 mark)

AETIOLOGY / PATHOGENESIS (1 mark)

• Specific nodules undergo genetic mutation leading to clonal expansion and autonomous hormone production independent of TSH
• Jod-Basedow effect - pharmacological doses of iodine (contrast media, amiodarone) precipitate hyperthyroidism, especially in iodine-deficient areas
• In some cases, internodular thyroid tissue is overactive; in others, one or more nodules are autonomously active
• Natural history: patient has a goitre for many years, toxicity develops later (middle age to elderly)

CLINICAL FEATURES (3 marks)

A. Symptoms

• Slowly enlarging, painless neck swelling present for years before toxicity
• Sudden painful enlargement if haemorrhage occurs into a nodule

• Palpitations
• Atrial fibrillation (AF) - pulse irregular in rate and rhythm (most important sign)
• Precordial pain and exhaustion
• Heart failure in late/untreated cases

• Dysphagia (difficulty swallowing solids)
• Dyspnoea (worse at night, on exertion)
• Stridor, engorged neck veins
• Hoarseness (if recurrent laryngeal nerve compressed)

• Weight loss despite good appetite
• Heat intolerance, excessive sweating
• Weakness, fatigue

B. Signs

Key Distinguishing Point: Unlike primary toxic goitre (Graves' disease) - NO exophthalmos, NO tongue tremor. Brunt falls on cardiovascular system. (S Das)

INVESTIGATIONS (2 marks)

• Serum TSH - suppressed (low/undetectable)
• Serum T3, T4 - elevated

• Indicated whenever toxicity is associated with nodularity
• Shows "hot" (autonomously functioning) nodules with suppression of surrounding normal tissue
• Localises hyperactive areas

• Determines solid vs. cystic nature
• Features of malignancy: microcalcification, increased vascularity, capsular breach, nodal involvement

• Done under USG guidance
• Rules out malignancy in dominant/suspicious nodules

• ECG - AF, tachyarrhythmias
• Chest X-ray / CT scan - tracheal compression, retrosternal extension
• Autoantibody titres - TSH receptor antibodies (absent in TMNG, unlike Graves')

TREATMENT (3 marks)

A. Medical Treatment (Antithyroid Drugs) - Temporary/Preparatory

• Carbimazole or Propylthiouracil (PTU)
• Used to render the patient euthyroid before surgery or radioiodine
• Cannot cure TMNG - toxicity recurs on stopping drugs (tissue is autonomous)
• Can be continued indefinitely if surgery/radioiodine is contraindicated

• Propranolol (beta-blocker) - rapidly controls palpitations, tachycardia, tremor; higher doses needed due to accelerated clearance
• Anticoagulation (Warfarin/NOAC) - mandatory if AF present, to prevent stroke/thromboembolism

B. Radioiodine (¹³¹I) - Definitive Treatment of Choice

• Preferred for most patients, especially elderly
• Renders patient euthyroid with antithyroid drugs first; drugs stopped 3-7 days before treatment
• Ablates autonomously functioning thyroid tissue
• May need repeat doses
• Leads to hypothyroidism over time → lifelong thyroxine replacement

C. Surgery - Subtotal / Total Thyroidectomy

• Large compressive goitre (dyspnoea, dysphagia)
• Suspected malignancy
• Retrosternal/intrathoracic extension
• Failed or contraindicated radioiodine
• Patient preference / cosmesis

1. Antithyroid drugs (Carbimazole/PTU) for 6-8 weeks to achieve euthyroid state
2. Lugol's iodine for 10 days before surgery (reduces vascularity, prevents thyroid storm)
3. Beta-blockers (Propranolol)

1. Recurrence of thyrotoxicosis (~5% with subtotal)
2. Permanent hypoparathyroidism (hypocalcaemia) - injury to parathyroids
3. Recurrent laryngeal nerve injury - hoarseness, voice change
4. Hypothyroidism - requires thyroxine replacement
5. Reactionary haemorrhage (rare but dangerous - can compress trachea)
6. Thyroid storm (if operated on untreated thyrotoxic patient)

COMPLICATIONS OF UNTREATED TMNG (mentioned for complete answer)

• Atrial fibrillation and heart failure
• Tracheal compression → dyspnoea, stridor
• Malignant transformation (~4%)
• Haemorrhage into nodule
• Thyroid storm (rare)

QUICK REVISION TABLE (For last-minute review)

Word count guide: This answer written in full is approximately 800-900 words - ideal for a 10-mark question in a 3-hour paper (allocate ~15-18 minutes).