What is the appropriate management for a patient presenting with symptoms suggestive of hypothyroidism, such as fatigue, weight gain, and cold intolerance, along with mild thyromegaly on physical examination?

Management of Suspected Primary Hypothyroidism with Thyromegaly

The planned thyroid ultrasound should be removed from the workup, as imaging has no role in the diagnosis or management of primary hypothyroidism in adults. 1

Initial Laboratory Workup

Your planned laboratory evaluation is appropriate and should proceed as outlined:

• TSH and Free T4 are the essential tests to confirm primary hypothyroidism, where TSH will be elevated with low or normal free T4 1, 2
• TPO antibodies help identify Hashimoto thyroiditis (chronic autoimmune thyroiditis), the most common cause of hypothyroidism in iodine-sufficient areas, accounting for up to 85% of cases 3
• Morning cortisol and ACTH should be added if there is any suspicion of central hypothyroidism (though unlikely given the clinical presentation), as adrenal insufficiency must be ruled out before starting thyroid hormone replacement 2, 4

Imaging Considerations

The ACR Appropriateness Criteria explicitly state there is no role for thyroid ultrasound in the workup of primary hypothyroidism in adults. 1 Imaging does not help differentiate among causes of hypothyroidism, and all causes will show decreased radioiodine uptake. 1

However, thyroid ultrasound should be performed only if:

• Discrete thyroid nodules are palpated (your exam notes "no nodules palpated," so this does not apply) 3
• Nodules develop during follow-up to evaluate malignancy risk 3

The mild thyromegaly noted on exam is consistent with Hashimoto thyroiditis and does not require imaging evaluation. 3

Treatment Initiation Algorithm

If TSH is elevated and free T4 is low (overt hypothyroidism):

• Start levothyroxine 1.6 mcg/kg/day (approximately 100 mcg daily for this 147-lb patient) 1, 5
• For this 32-year-old patient without cardiac disease or multiple comorbidities, full replacement dosing can be started immediately 1
• Recheck TSH and free T4 in 6-8 weeks after starting treatment 1, 3

If TSH is 4.5-10 mIU/L with normal free T4 (subclinical hypothyroidism):

• If asymptomatic: Monitor TSH every 4-6 weeks; approximately 40% may normalize spontaneously 6
• If symptomatic (as this patient is): Consider treatment, especially given positive family history suggesting autoimmune predisposition 4, 6

If TSH is persistently >10 mIU/L (even with normal free T4):

• Initiate levothyroxine replacement therapy 1, 4
• This threshold indicates higher risk of progression to overt hypothyroidism (2-5% annually) and cardiovascular complications 4, 6

Critical Pitfalls to Avoid

Do not start thyroid hormone replacement before ruling out adrenal insufficiency if central hypothyroidism is suspected (low/normal TSH with low free T4), as this can precipitate adrenal crisis. 1, 2 However, this patient's presentation strongly suggests primary hypothyroidism.

Avoid ordering unnecessary imaging. The thyromegaly in this clinical context (young woman with hypothyroid symptoms and family history) is almost certainly Hashimoto thyroiditis and requires no imaging unless discrete nodules are palpated. 1

Monitor for overtreatment. Target TSH should be 0.5-2.0 mIU/L; over-replacement increases risk of atrial fibrillation and osteoporosis. 4

Follow-Up Management

• Recheck TSH (and optionally free T4) every 6-8 weeks while titrating levothyroxine to achieve TSH within reference range 1
• Once stable, repeat testing every 6-12 months or with symptom changes 1
• Levothyroxine should be taken on an empty stomach, 30-60 minutes before breakfast, avoiding iron, calcium supplements, and antacids within 4 hours 7
• Inform the patient that symptom improvement may take several weeks and that replacement therapy is typically lifelong 7, 5