Thyroid Ultrasound in Suspected Hypothyroidism
There is no role for thyroid ultrasound in the initial workup of hypothyroidism in adults. 1 Imaging for thyroid morphology does not help differentiate among causes of hypothyroidism, and all causes of hypothyroidism will have decreased radioiodine uptake.
Diagnostic Approach for Suspected Hypothyroidism
Initial Laboratory Evaluation
- Thyroid function tests (TSH and free T4) are the cornerstone for evaluating thyroid function
- TSH is the most sensitive indicator, with Free T4 helping distinguish between primary and central hypothyroidism
- Thyroid autoantibody testing (TPOAb and TgAb) may be helpful in suspected Hashimoto's thyroiditis 2
When Ultrasound Is NOT Indicated
- Patients with normal neck examination and laboratory-confirmed hypothyroidism
- Patients with subclinical hypothyroidism (mildly elevated TSH with normal free T4) 3
- Routine monitoring of known hypothyroidism
Specific Scenarios When Ultrasound IS Indicated
- Palpable thyroid nodule or goiter - Ultrasound should be performed if a nodule or goiter is detected on physical examination 1
- History of head and neck radiation - Patients with prior radiation exposure have increased risk of thyroid malignancy 4
- Suspicious clinical features suggesting possible thyroid cancer:
- Very firm nodule
- Fixed to adjacent structures
- Rapidly growing nodule
- Enlarged regional lymph nodes
- Vocal cord paralysis
- Family history of thyroid cancer 5
Consequences of Inappropriate Ultrasound Use
Research has shown that approximately 7% of thyroid ultrasounds are inappropriately ordered in patients with hypothyroidism 6. This leads to:
- Unnecessary medical encounters
- Financial burden (average charge of $851 per patient)
- Potential detection of incidental nodules (thyroid incidentalomas) that may lead to unnecessary additional testing and procedures
- Patients younger than 50 years are at higher risk of receiving inappropriate ultrasound (odds ratio: 2.37) 6
Management of Hypothyroidism
- Levothyroxine replacement therapy is the standard treatment, started at 1.5 to 1.8 mcg per kg per day
- Lower starting doses (12.5 to 50 mcg per day) for patients older than 60 years or with known/suspected heart disease
- Pregnant women require dose increases (approximately 30% higher weekly dosage) 7
- TSH monitoring every 4-6 weeks until stable, then every 3-6 months 2
Special Considerations in Pediatric Patients
In pediatric patients, ultrasound may be more appropriate in the evaluation of congenital hypothyroidism to assess for:
- Thyroid dysgenesis
- Thyroid ectopia
- Thyroid agenesis
- Dyshormonogenesis 8
Key Pitfalls to Avoid
- Ordering thyroid ultrasound based solely on abnormal thyroid function tests
- Using ultrasound as a screening tool in asymptomatic patients with hypothyroidism
- Failure to recognize that the American College of Radiology Appropriateness Criteria explicitly states there is no role for imaging in the workup of hypothyroidism in adults 1
- Ordering ultrasound in patients with subclinical hypothyroidism without other risk factors for malignancy
Remember that the Endocrine Society, through the Choosing Wisely® initiative, specifically recommends against ordering thyroid ultrasounds in individuals with subclinical or overt hypothyroidism who have a normal neck examination 6.