What is the initial workup and treatment approach for a patient suspected of having hyperthyroidism?

Initial Workup and Treatment Approach for Suspected Hyperthyroidism

The initial workup for suspected hyperthyroidism should include thyroid function tests (TSH, free T4, and total T3), followed by determination of etiology through TSH-receptor antibody testing and thyroid imaging, with treatment selection based on the underlying cause. 1, 2

Diagnostic Workup

Step 1: Laboratory Assessment

• Measure thyroid function tests:
  • TSH (typically suppressed in hyperthyroidism)
  • Free T4 (elevated in overt hyperthyroidism, normal in subclinical hyperthyroidism)
  • Total or free T3 (often elevated, especially in Graves' disease) 1, 3
• Repeat testing in 4-6 weeks to confirm diagnosis if initial results are borderline 4

Step 2: Determine Etiology

• Measure TSH-receptor antibodies (TRAb) to diagnose Graves' disease 2
• Consider thyroid peroxidase (TPO) antibodies to help identify autoimmune thyroiditis 2
• Perform thyroid ultrasonography to evaluate for nodules, goiter, or thyroiditis 2
• Consider thyroid scintigraphy (radioiodine uptake scan) if:
  • Thyroid nodules are present
  • Etiology remains unclear after initial testing
  • Need to differentiate between causes of hyperthyroidism (e.g., Graves' disease vs. thyroiditis) 1, 3

Treatment Approach

For Graves' Disease (most common cause, ~70% of cases)

1. First-line treatment: Antithyroid drugs (ATDs)

   • Methimazole (preferred in most cases)
     • Starting dose: 1.6 mcg/kg/day for patients <70 years without cardiac disease
     • Lower starting dose (25-50 mcg/day) for elderly or those with cardiac conditions 4
   • Propylthiouracil (preferred in first trimester of pregnancy due to lower risk of congenital malformations) 5, 6
   • Standard course: 12-18 months (recurrence rate ~50%) 2
   • Long-term treatment (5-10 years) may be considered (recurrence rate ~15%) 2

2. Alternative treatments:

   • Radioactive iodine ablation (most widely used in US)
   • Surgical thyroidectomy 7

For Toxic Nodular Goiter (~16% of cases)

• Radioactive iodine ablation (preferred)
• Surgical thyroidectomy
• Rarely, radiofrequency ablation 2

For Thyroiditis (~3% of cases)

• Observation if mild and asymptomatic
• Supportive care for symptom management
• Glucocorticoids for severe cases 3

Monitoring and Follow-up

• Monitor thyroid function tests every 4-6 weeks until stable, then every 6-12 months 4
• Adjust ATD dose in increments of 12.5-25 mcg until optimal replacement is achieved 4
• Target TSH range:
  • 0.5-2.0 mIU/L for patients under 70 years without cardiac disease
  • 1.0-4.0 mIU/L for elderly patients or those with cardiac conditions 4

Important Precautions

For Methimazole

• Monitor for signs of agranulocytosis (sore throat, fever, general malaise)
• Perform white blood cell counts if concerning symptoms develop
• Watch for vasculitis (rash, hematuria, decreased urine output, dyspnea)
• Monitor prothrombin time before surgical procedures 5

For Propylthiouracil

• Monitor for hepatotoxicity (anorexia, pruritus, jaundice, right upper quadrant pain)
• Check liver function tests (bilirubin, alkaline phosphatase, ALT/AST) if symptoms develop
• Watch for agranulocytosis and vasculitis
• Consider switching to methimazole after first trimester in pregnant women 6

Special Considerations

• For pregnant women: Propylthiouracil preferred in first trimester, then switch to methimazole for second and third trimesters 5, 6
• For elderly patients: Start with lower doses of ATDs and target higher TSH range (1.0-4.0 mIU/L) 4
• For subclinical hyperthyroidism: Treatment recommended for patients >65 years or with persistent TSH <0.1 mIU/L 1
• For patients with cardiac conditions: Consider beta-blockers for symptomatic relief during initial treatment 4