← All postsHyperthyroidism: Definition, Causes, Diagnosis & Stepwise Management Guide [MMI, PTU]
EN18 October 2025· 4 min read
1️⃣. Definition and Pathophysiology
Hyperthyroidism = overproduction of thyroid hormones (T3, T4) by the thyroid gland → suppressed TSH.
Thyrotoxicosis = clinical syndrome of excess circulating thyroid hormone, regardless of cause (e.g., Graves, thyroiditis, toxic nodular goiter).
Pathophysiology summary:
- ↑ T3/T4 → ↑ basal metabolic rate
- ↑ β-adrenergic receptor sensitivity → palpitations, tremor
- Feedback inhibition → ↓ TSH from pituitary
2️⃣. Common Causes
| Category | Disease | Mechanism |
|---|
| Autoimmune | Graves’ disease | TRAb stimulates TSH receptor → overproduction |
| Toxic nodular disease | Toxic multinodular goiter, Toxic adenoma | Autonomous hormone production |
| Inflammatory | Subacute thyroiditis, Silent thyroiditis, Postpartum thyroiditis | Destruction of follicles → hormone leakage |
| Iatrogenic | Amiodarone, excess levothyroxine, iodine exposure | Overreplacement / iodine-induced |
| Rare | TSH-secreting pituitary adenoma, Struma ovarii | Ectopic production |
3️⃣. Diagnosis — Lab Interpretation
| Parameter | Normal Range | Hyperthyroid Pattern |
|---|
| TSH | 0.4 – 4.0 mIU/L | ↓ (often < 0.01) |
| Free T4 (FT4) | 0.8 – 1.8 ng/dL (10–23 pmol/L) | ↑ |
| Free T3 (FT3) | 2.3 – 4.2 pg/mL (3.5–6.5 pmol/L) | ↑↑ (sometimes disproportionately high → T3 toxicosis) |
🔹 T3 toxicosis: TSH ↓, FT3 ↑, FT4 normal → early Graves or toxic nodular goiter
🔹 Subclinical hyperthyroidism: TSH ↓, FT3/FT4 normal → mild or early disease
4️⃣. Confirming the Cause (Etiologic Workup)
| Test | Purpose | Findings |
|---|
| TSH receptor antibody (TRAb) | Confirm Graves’ disease | Positive = Graves |
| Thyroid peroxidase antibody (Anti-TPO) | Autoimmune marker | + in Graves or Hashimoto |
| RAI Uptake Scan | Identify pattern of activity | Diffuse uptake = Graves Patchy = Toxic MNG Low uptake = Thyroiditis |
| Thyroid Ultrasound with Doppler | Assess structure and vascularity | "Thyroid inferno" pattern in Graves |
| Baseline labs | Safety before drugs | CBC, LFT, Pregnancy test (if female) |
5️⃣. Management — Overview
🎯 Goals:
- Control symptoms (tachycardia, tremor)
- Normalize thyroid hormone levels
- Prevent complications (thyroid storm, arrhythmia, osteoporosis)
- Treat the underlying cause
6️⃣. Stepwise Management Algorithm
A. Symptomatic Control
| Drug | Dose | Purpose |
|---|
| Propranolol | 20–40 mg PO every 6–8 hours | Control palpitations, tremor, anxiety; inhibits T4→T3 conversion |
| Alternative (asthma) | Atenolol 25–50 mg PO daily | Cardioselective option |
B. Definitive Control of Hormone Synthesis
🩸 1. Antithyroid Drugs (First-Line for Most)
| Drug | Adult Dose | Notes |
| Methimazole (MMI) | Mild: 10 mg/dayModerate: 20–30 mg/daySevere: 40 mg/day (divided 2–3 times daily)* | Preferred (longer half-life, safer) |
| Propylthiouracil (PTU) | Initial: 100 mg PO tidMaintenance: 50 mg tid | Use in 1st trimester pregnancy or thyroid storm |
| Duration: | 12–18 months | Monitor TSH, FT4 q4–6 weeks |
| Monitor: | CBC, LFT | Risk: agranulocytosis, hepatotoxicity |
| Warning: | Stop immediately if fever/sore throat (→ CBC to check WBC). | |
✅ Once euthyroid achieved → reduce MMI to 5–10 mg/day maintenance.
💉 2. Radioactive Iodine (RAI-131)
- Definitive treatment for most adults.
- Contraindicated in:
- Pregnancy / breastfeeding
- Severe ophthalmopathy (worsens after RAI)
- Goal: destroy thyroid tissue → hypothyroidism (then lifelong levothyroxine).
🩺 3. Surgery (Total or Subtotal Thyroidectomy)
Indications:
- Large goiter / compressive symptoms
- Suspicious or malignant nodule
- Drug intolerance / relapse after MMI
- Pregnancy (2nd trimester only)
Pre-op preparation:
- Achieve euthyroid with MMI/PTU
- Add potassium iodide 5 drops PO bid × 10 days before surgery to prevent thyroid storm.
C. Supportive Care
| Measure | Purpose |
| Adequate hydration | Replace increased metabolic losses |
| Nutrition | High-protein, high-calorie diet |
| Avoid excess iodine | E.g., seaweed, multivitamins |
| Stress control | Prevent adrenergic flare |
| Smoking cessation | Reduces risk of Graves’ ophthalmopathy |
7️⃣. Follow-up & Monitoring
| Parameter | Timeline | Purpose |
|---|
| TSH, FT4, FT3 | Every 4–6 weeks initially | Guide dose adjustment |
| CBC & LFT | Baseline, then if symptomatic | Detect agranulocytosis or hepatotoxicity |
| TRAb | At 12–18 months | Predict relapse or remission |
| After remission | Monitor yearly for relapse or hypothyroidism | |
8️⃣. Complications to Monitor
| Untreated | From Drugs |
|---|
| Thyroid storm (fever, tachycardia, delirium) | Agranulocytosis (neutropenia) |
| Atrial fibrillation | Hepatotoxicity (esp. PTU) |
| Osteoporosis, muscle wasting | Hypothyroidism (from overtreatment) |
9️⃣. Special Considerations
| Condition | Preferred Drug | Notes |
| Pregnancy (1st trimester) | PTU | Avoid MMI (teratogenic) |
| Pregnancy (2nd–3rd trimester) | MMI | PTU hepatotoxic |
| Thyroid storm | PTU + Propranolol + Steroid + Iodine | PTU preferred (blocks T4→T3) |
🔢 10. Drug Dosing Summary Table
| Drug | Starting Dose | Maintenance Dose | Max Dose | Route | Notes |
|---|
| Methimazole (MMI) | 10–30 mg/day | 5–15 mg/day | 40 mg/day | PO | Preferred; once daily ok |
| Propylthiouracil (PTU) | 100 mg tid | 50 mg tid | 600–900 mg/day | PO | Use in 1st trimester, thyroid storm |
| Propranolol | 20–40 mg q6h | 10–20 mg q6h or PRN | 160 mg/day | PO | Symptom control |
| Potassium iodide | 5 drops bid (SSKI) | Short-term pre-op | — | PO | Given after PTU in thyroid storm |
📉 11. Example Interpretation and Management (Your Case)
| Parameter | Result | Interpretation |
|---|
| TSH | 0.027 ↓ | Suppressed |
| FT3 | 7.82 ↑ | Markedly elevated |
| FT4 | 2.02 ↑ | Elevated |
| → Diagnosis: Primary hyperthyroidism (likely Graves’) | | |
Start:
- Methimazole 20 mg/day PO (moderate case)
- Propranolol 20 mg PO q6h
- Baseline CBC, LFT
- TRAb ± Ultrasound if not done
- Follow-up in 4–6 weeks
🧭 12. Treatment Targets
| Phase | Goal |
|---|
| Initial (4–6 wks) | Normalize FT4 (TSH may remain low for months) |
| Maintenance (3–6 mo) | Stable FT4 and TSH within range |
| Long-term (12–18 mo) | Attempt drug withdrawal if TRAb negative and patient euthyroid |
📚 Guideline References
- American Thyroid Association (ATA): Hyperthyroidism and Other Causes of Thyrotoxicosis, 2016.
- European Thyroid Association (ETA) Guideline 2018.
- Thai Endocrine Society Clinical Practice Guideline for Thyrotoxicosis (2021).
🩺 Keys for Exam
✅ MMI preferred (once-daily, less hepatotoxic).
✅ PTU only for pregnancy 1st trimester or thyroid storm.
✅ Always check CBC + LFT before starting.
✅ TRAb optional for diagnosis, essential for predicting remission.
✅ Follow FT4, not TSH, in early follow-up.
✅ If symptoms controlled but FT4 high → increase MMI dose.
✅ If FT4 normal but TSH still low → keep same dose, recheck in 6 wks.