How to diagnose toxic multinodular goiter?

Diagnosis of Toxic Multinodular Goiter

The diagnosis of toxic multinodular goiter requires a combination of thyroid function tests (particularly TSH and free T4), thyroid ultrasound, and thyroid scintigraphy, with the latter being essential to confirm autonomous functioning nodules. 1

Initial Diagnostic Steps

1. Thyroid Function Tests:

   • Measure TSH (will be suppressed or undetectable)
   • Measure free T4 (may be elevated or normal)
   • Measure free T3 (may be elevated, especially in T3 toxicosis cases)

2. Thyroid Ultrasound:

   • Confirms presence of multiple nodules
   • Evaluates nodule characteristics: size, echogenicity, borders
   • Shows heterogeneous echotexture with multiple solid nodules, often with ill-defined borders 2
   • Helps determine overall gland size and extent

3. Thyroid Scintigraphy (Radionuclide Scan):

   • Critical for diagnosis of toxic multinodular goiter
   • Shows uneven distribution of radiotracer with multiple hyperfunctioning ("hot") nodules 2
   • Differentiates from other causes of hyperthyroidism (e.g., Graves' disease)
   • The American College of Radiology specifically recommends thyroid scintigraphy in cases of hyperthyroidism to differentiate between Graves' disease, toxic adenoma, or toxic multinodular goiter 1

Clinical Presentation to Consider

• Cardiac manifestations are often predominant (especially in elderly patients):
  • Atrial fibrillation
  • Other arrhythmias
  • Tachycardia
• Subclinical phase often precedes overt symptoms (normal thyroid hormones with suppressed TSH) 2
• Absence of ophthalmopathy (unlike Graves' disease) 1
• Compressive symptoms may be present:
  • Dysphagia
  • Dyspnea
  • Voice changes
  • Sensation of neck pressure

Additional Imaging When Needed

• CT or MRI of the neck is recommended when:
  • Substernal extension is suspected
  • Retropharyngeal extension is suspected
  • Tracheal compression is suspected 1, 3
  • CT is preferred over MRI due to less respiratory motion artifact 3

Common Pitfalls and Caveats

1. Don't miss subclinical hyperthyroidism: Many patients with toxic multinodular goiter have a prolonged subclinical phase before developing overt symptoms 2

2. Don't confuse with Graves' disease: Unlike Graves' disease, toxic multinodular goiter lacks ophthalmopathy and has a different scintigraphy pattern 1

3. Don't rely solely on ultrasound: While ultrasound confirms nodularity, it cannot determine functionality of nodules - scintigraphy is essential 3, 1

4. Consider age-related presentation: In elderly patients, cardiac symptoms may be the predominant or only manifestation 2

5. Don't forget to evaluate for malignancy: Although functioning nodules have lower risk of malignancy, suspicious nodules should still undergo fine needle aspiration biopsy 1

By following this diagnostic approach, toxic multinodular goiter can be accurately identified and distinguished from other causes of hyperthyroidism, allowing for appropriate treatment planning.