What is the treatment for a patient with hyperthyroidism, indicated by elevated Free Triiodothyronine (FT3) levels and low Thyroid-Stimulating Hormone (TSH) levels?

Hyperthyroidism Treatment

Immediate Assessment and Diagnosis

Your laboratory values (FT3 5.4 with TSH 0.04) confirm overt hyperthyroidism requiring treatment. The suppressed TSH (<0.1 mIU/L) combined with elevated free T3 indicates autonomous thyroid hormone production that must be addressed to prevent serious complications including cardiac arrhythmias, heart failure, osteoporosis, and increased mortality 1, 2.

Determining the Cause

Before initiating treatment, you need a nosological diagnosis to identify which disease is causing your hyperthyroidism 1:

• Measure TSH-receptor antibodies (TSH-R-Ab) - if positive, this confirms Graves' disease, which accounts for 70% of hyperthyroidism cases 1, 3
• Obtain thyroid ultrasonography to assess for toxic nodular goitre (16% of cases) versus diffuse enlargement 1
• If the diagnosis remains unclear or nodules are present, thyroid scintigraphy is recommended to differentiate between Graves' disease (diffuse uptake), toxic nodular goitre (focal uptake), and thyroiditis (low uptake) 2, 3

First-Line Treatment: Antithyroid Drugs

Methimazole (MMI) is the preferred antithyroid drug for initial treatment of Graves' hyperthyroidism, with a standard course of 12-18 months 3. Propylthiouracil (PTU) is reserved for specific situations 4, 5, 3.

Methimazole Dosing and Monitoring

• Start methimazole at an appropriate dose based on disease severity - typical initial doses range from 10-40 mg daily depending on the degree of thyroid hormone elevation 4, 3
• Monitor thyroid function tests (TSH, free T4, free T3) periodically during therapy to assess response and adjust dosing 4
• Once clinical hyperthyroidism resolves and TSH begins rising, reduce the methimazole dose to a lower maintenance level 4
• Continue treatment for 12-18 months, then measure TSH-R-Ab - if persistently elevated, consider continuing MMI for another 12 months, or opt for definitive therapy with radioactive iodine or thyroidectomy 3

When to Use Propylthiouracil Instead

• If you are pregnant or planning pregnancy - switch to PTU during the first trimester due to rare congenital malformations associated with methimazole, then consider switching back to methimazole for the second and third trimesters 4, 5, 3
• PTU has the additional benefit of inhibiting peripheral conversion of T4 to T3, which may provide faster symptom relief in severe cases 6

Alternative Definitive Treatments

Radioactive Iodine (RAI)

• RAI is the preferred definitive treatment for toxic nodular goitre and is an option for Graves' disease after failed medical therapy 1, 3
• RAI is contraindicated if you have active or severe thyroid eye disease (Graves' orbitopathy), and steroid prophylaxis is required if you have mild/active orbitopathy 3

Thyroidectomy

• Total thyroidectomy should be performed by an experienced high-volume thyroid surgeon if you choose surgical management 3
• Surgery is preferred if you have large goiters causing compressive symptoms (dysphagia, orthopnea, voice changes) or if RAI is contraindicated 2

Critical Monitoring and Safety Considerations

Immediate Reporting Requirements

• Report immediately if you develop sore throat, skin eruptions, fever, headache, or general malaise - these may indicate agranulocytosis, a serious side effect requiring white blood cell count assessment 4, 5
• Report symptoms of vasculitis including new rash, hematuria, decreased urine output, dyspnea, or hemoptysis - severe complications and death have occurred with both antithyroid drugs 4, 5
• If taking methimazole, report symptoms of hepatic dysfunction (anorexia, pruritus, jaundice, light-colored stools, dark urine, right upper quadrant pain), particularly in the first 6 months 5

Drug Interactions to Monitor

• If you take warfarin or other oral anticoagulants, additional PT/INR monitoring is needed as antithyroid drugs may increase anticoagulant activity 4, 5
• If you take beta-blockers, digoxin, or theophylline, dose reductions may be needed as you become euthyroid, since hyperthyroidism increases clearance of these medications 4, 5

Expected Outcomes and Long-Term Management

• Approximately 50% of patients relapse after completing a 12-18 month course of antithyroid drugs 1
• Risk factors for recurrence include age <40 years, FT4 ≥40 pmol/L, TSH-binding inhibitory immunoglobulins >6 U/L, and goiter size ≥WHO grade 2 1
• Long-term treatment with antithyroid drugs (5-10 years) is associated with fewer recurrences (15%) compared to short-term treatment and is a feasible option 1
• If you relapse after completing antithyroid drug therapy, definitive treatment with RAI or thyroidectomy is recommended, though continued long-term low-dose methimazole can be considered 3

Common Pitfalls to Avoid

• Do not delay treatment - untreated hyperthyroidism causes cardiac arrhythmias, heart failure, unintentional weight loss, and is associated with increased mortality 2
• Do not assume all hyperthyroidism requires the same treatment - thyroiditis-induced thyrotoxicosis is usually mild and transient, requiring only supportive care or steroids in severe cases, not antithyroid drugs 1
• Do not continue methimazole if you become pregnant - switch to PTU immediately for the first trimester 4, 3