Surgery LAQ Answer

DIAGNOSIS: Primary Hyperthyroidism - Most likely Graves' Disease

CLINICAL REASONING

ETIOPATHOLOGY

Graves' Disease (Primary Autoimmune Hyperthyroidism)

1. Autoimmune basis: Graves' disease is caused by the production of autoantibodies against multiple thyroid proteins, most importantly the TSH receptor.
2. Thyroid-stimulating immunoglobulin (TSI): Present in ~90% of patients. TSI binds to the TSH receptor and mimics its actions - stimulating adenylyl cyclase, increasing cAMP, and causing continuous release of T3 and T4 independent of the pituitary feedback loop. TSH levels fall (negative feedback from high T3/T4), but thyroid stimulation continues unchecked.
3. TSH receptor blocking antibodies may also be present in a minority; these paradoxically cause hypothyroidism.
4. Genetic susceptibility: Concordance in monozygotic twins is 30-40% vs <5% in dizygotic. Polymorphisms in immune-function genes (CTLA4, PTPN22, IL2RA) and the TSHR gene are implicated. Associated with HLA-DR3.
5. Triggers: Emotional stress, infection, pregnancy (postpartum), iodine excess, smoking.

• Symmetrical diffuse enlargement (weight may exceed 80 g)
• Histology: follicular epithelial cells are tall and crowded; form small papillae projecting into follicle lumen (without fibrovascular cores - unlike papillary carcinoma)
• Colloid is pale with scalloped margins (actively resorbed)
• Lymphoid infiltrates (T cells, B cells, plasma cells) throughout interstitium; germinal centers common

• Raised basal metabolic rate - heat intolerance, weight loss despite hyperphagia
• Catecholamine sensitization - palpitations, tremor, sweating
• Protein catabolism - proximal myopathy, muscle wasting
• Hypothalamic-pituitary-gonadal axis disruption - menstrual irregularities

INVESTIGATIONS

• Serum TSH (most sensitive): Suppressed (< 0.1 mU/L) - primary screening test
• Free T4 (fT4): Elevated (normal: 12-28 pmol/L)
• Free T3 (fT3): Elevated - especially useful in T3 thyrotoxicosis where fT4 may be normal
• TSI / TRAb (TSH receptor antibodies): Positive in Graves' disease; confirms diagnosis
• Anti-TPO, anti-thyroglobulin antibodies: May be elevated
• TFTs: T3 and T4 elevated; TSH suppressed

• Thyroid ultrasound: Diffuse goiter, increased vascularity (Doppler), rules out nodular disease
• Radioactive iodine uptake (RAIU): Diffusely increased (> 35% at 24 hours) - confirms increased thyroid activity; distinguishes Graves' from thyroiditis (where RAIU is low)
• Thyroid scan (Tc-99m or I-123): Diffuse homogeneous uptake in Graves'; hot nodule(s) in toxic MNG

• ECG: Sinus tachycardia, AF
• Serum calcium: Mild hypercalcemia possible
• CBC: Mild leukopenia
• Blood glucose (hyperglycemia possible)
• Slit lamp / ophthalmology referral if exophthalmos suspected

MANAGEMENT

A. MEDICAL MANAGEMENT (First-line / Pre-operative preparation)

• Carbimazole (10-15 mg TID, or 30-40 mg/day): Preferred in India/UK. Inhibits thyroid peroxidase, blocking organification of iodine and thyroid hormone synthesis. Also has some immunosuppressive effect.
• Propylthiouracil (PTU) (100-150 mg TID): Used in pregnancy (first trimester) and thyroid storm. Additionally inhibits peripheral conversion of T4 to T3.
• "Block and replace" regimen: High-dose thionamide to block all synthesis + levothyroxine replacement to maintain euthyroidism.
• Titration regimen: Dose adjusted based on TFTs to achieve euthyroid state.
• Duration: 12-18 months; ~50% remission rate in Graves'.
• Side effects: Agranulocytosis (warn patient to report sore throat/fever), rash, hepatotoxicity (PTU).

• Propranolol 40-80 mg TID: Reduces sympathetic symptoms (palpitations, tremor, sweating, heat intolerance) by blocking beta-adrenergic effects. Does not reduce thyroid hormone levels but also inhibits T4 to T3 conversion at high doses.

• Potassium iodide (Lugol's solution) given 10-14 days before surgery.
• Causes involution of thyroid epithelium and accumulation of colloid (Wolff-Chaikoff effect), reducing vascularity and making gland firmer/less friable - reduces intraoperative bleeding.

B. RADIOACTIVE IODINE (RAI) - I-131

• Taken orally as a capsule/solution
• Selectively absorbed by thyroid follicular cells; beta emission destroys thyroid tissue
• Indications: Elderly patients, cardiac disease, failure of drug therapy, recurrence after surgery, patient preference
• Contraindications: Pregnancy, breastfeeding, large compressive goiter (may worsen swelling initially), moderate-severe active Graves' ophthalmopathy
• Outcome: Euthyroid or hypothyroid in 6-12 months; lifelong thyroxine may be needed
• Advantages: Safe, non-invasive, curative
• Note: This is first-line in elderly and those with cardiac dysfunction.

C. SURGICAL MANAGEMENT (Definitive)

• Large goiter with compressive symptoms (dysphagia, stridor, dyspnea)
• Failed or recurrent disease after antithyroid drugs
• Patient preference (young woman of childbearing age like this patient)
• Suspected or confirmed thyroid malignancy
• Toxic multinodular goiter (RAI less effective)
• Graves' ophthalmopathy (surgery preferred over RAI which can worsen eye disease)
• Allergy or side effects to antithyroid drugs
• Non-compliant patients

1. Render euthyroid with carbimazole/PTU for 6-8 weeks
2. Propranolol to control symptoms
3. Lugol's iodine for 10-14 days pre-op to reduce vascularity
4. Anesthetic assessment, calcium/PTH baseline, vocal cord check (indirect laryngoscopy)

• Total thyroidectomy (currently preferred): Eliminates all disease; removes risk of recurrence; no residual thyroid tissue (avoids reoperation); requires lifelong thyroxine.
• Bilateral subtotal thyroidectomy (historical): Leaving ~2-4 g of thyroid tissue bilaterally near the recurrent laryngeal nerves; carries risk of recurrence (15-25%) but preserves some function.
• Near-total thyroidectomy: Leaves <1 g on one side; low recurrence, acceptable safety.

• Monitor calcium (4-hourly for 24 hours)
• Monitor for stridor (hematoma, bilateral RLN palsy)
• Start levothyroxine once euthyroid confirmed
• Long-term TFT monitoring

SUMMARY TABLE