Overview
This podcast episode provides an expert review of hyperthyroidism, including definitions, etiologies, diagnostic approaches, management strategies, treatment risks, and considerations for special populations such as pregnant women.
Definitions and Terminology
- Thyrotoxicosis refers to excess circulating thyroid hormone, while hyperthyroidism specifically means increased thyroid hormone synthesis and secretion.
- Overt hyperthyroidism is defined biochemically by low TSH and elevated T3 and/or T4.
- Subclinical hyperthyroidism presents as low TSH with normal peripheral thyroid hormones.
Common Causes and Epidemiology
- Graves disease is the most common cause of hyperthyroidism globally, affecting up to 2% of women and 1% of men.
- Toxic nodules and thyroiditis are also common; toxic nodules are more prevalent in regions with iodine deficiency.
- Medications such as amiodarone and immune checkpoint inhibitors can cause distinct patterns of thyrotoxicosis.
Diagnostic Approach
- Initial screening is always with serum TSH; if low, follow with measurements of T3 and T4.
- Free T4 and total T3 are recommended for further hormone evaluation; avoid free T3 assays.
- Measure TSH receptor antibodies (TRAb or TSI) to diagnose Graves disease; TPO antibodies may help identify thyroiditis.
- Radioactive iodine uptake or scan aids in distinguishing Graves disease, toxic nodules, and thyroiditis.
Clinical Presentation
- Classic symptoms include palpitations, tremor, heat intolerance, weight loss, sleep disruption, anxiety, and fatigue.
- Older adults may exhibit "apathetic hyperthyroidism" with subtler symptoms.
Treatment Strategies
- Thyroiditis often resolves spontaneously; beta blockers are used for symptom relief.
- Graves disease and toxic nodules require anti-thyroid drugs (methimazole is first-line, PTU reserved for specific cases), radioactive iodine, or surgery.
- Definitive therapies (surgery or radioactive iodine) are considered if remission is unlikely or not achieved.
Management of Subclinical Hyperthyroidism
- Monitor for progression to overt disease, especially in asymptomatic patients.
- Consider treatment if TSH is consistently below 0.1 in patients over 65, or those with osteoporosis or cardiovascular risk.
- Most patients are asymptomatic; medication risks may outweigh benefits unless symptoms are significant.
Risks and Adverse Effects of Treatment
- Anti-thyroid drugs can cause rare agranulocytosis, teratogenicity (methimazole > PTU), and liver dysfunction (severe with PTU).
- Radioactive iodine requires post-treatment precautions due to radiation emission and has a potential, but low, long-term cancer risk.
- Surgery carries risks of nerve and parathyroid gland injury; experienced surgeons are preferred.
Remission in Graves Disease
- Approximately 50% of Graves patients may achieve remission with anti-thyroid drugs after 12-18 months.
- Severe baseline disease, large goiters, and high antibody titers reduce remission likelihood.
- Long-term drug therapy or definitive therapies are options if remission is not achieved.
Special Considerations: Pregnancy
- Preconception counseling is critical for women of childbearing age with hyperthyroidism, requiring individualized, patient-centered discussions.
Recommendations / Advice
- Measure TSH first, then proceed with free T4 and total T3 for abnormal findings.
- Use TRAb/TSI for Graves disease diagnosis; reserve TPO antibodies for suspected thyroiditis.
- Counsel all patients about treatment risks and ensure preconception planning for women.