Hyperthyroidism: Definition, Causes, Diagnosis & Stepwise Management Guide [MMI, PTU]
- Mayta

- Oct 18
- 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
3️⃣. Diagnosis — Lab Interpretation
🔹 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)
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
B. Definitive Control of Hormone Synthesis
🩸 1. Antithyroid Drugs (First-Line for Most)
✅ 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
7️⃣. Follow-up & Monitoring
8️⃣. Complications to Monitor
9️⃣. Special Considerations
🔢 10. Drug Dosing Summary Table
📉 11. Example Interpretation and Management (Your Case)
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
📚 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.





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