From the Guidelines
Subclinical hyperthyroidism has significant implications, including an increased risk of bone loss and atrial fibrillation, particularly in the elderly.
Key Implications
- Bone Loss: Prolonged subclinical hyperthyroidism can lead to a decline in bone mineral density (BMD), especially in postmenopausal women 1.
- Atrial Fibrillation: There is a concern about the risk of atrial fibrillation, particularly in older adults 1.
- Treatment Considerations: Treatment should be considered for patients with subclinical hyperthyroidism who are older than 60 years, have a history of heart disease, osteopenia, or osteoporosis, or have symptoms suggestive of hyperthyroidism 1.
Management
- Threshold for Treatment: A TSH level lower than 0.1 mIU/L is considered a threshold for treatment, especially in older adults or those with underlying health conditions 1.
- Monitoring: Younger individuals with subclinical hyperthyroidism and serum TSH persistently lower than 0.1 mIU/L may be offered therapy or follow-up depending on individual considerations 1.
Clinical Considerations
- Progression to Overt Hyperthyroidism: An estimated 1% to 2% of persons with TSH levels less than 0.1 mIU/L develop overt hyperthyroidism 1.
- Reversion to Euthyroid State: One quarter of persons with subclinical hyperthyroidism revert to a euthyroid state without medical intervention over time 1.
From the Research
Implications of Subclinical Hyperthyroidism
The implications of subclinical hyperthyroidism are varied and can have significant effects on the cardiovascular system and bone health. Some of the key implications include:
- Increased risk of atrial fibrillation, particularly in older individuals with TSH levels <0.1 mU/L 2, 3
- Potential increase in all-cause and cardiovascular mortality, with the risk increasing with age and associated with the lowest TSH levels 2
- Association with bone loss and osteoporosis, particularly in older adults 4, 5, 6
- Potential cognitive decline in some individuals 5
- Increased risk of cardiovascular-related adverse outcomes, such as heart failure and stroke 3
Treatment Considerations
Treatment for subclinical hyperthyroidism is recommended for patients at highest risk of osteoporosis and cardiovascular disease, such as those older than 65 years or with persistent serum thyrotropin level less than 0.1 mIU/L 4. The decision to treat subclinical hyperthyroidism is made on a case-by-case basis, taking into account the patient's age, the degree of TSH suppression, symptoms consistent with hyperthyroidism, and overall cardiovascular and osteoporotic fracture risks 2, 5, 6. Treatment options may include observation without therapy, initiation of antithyroid medications, or pursuit of radioiodine therapy or thyroid surgery 5.
Risk Factors and Evaluation
Subclinical hyperthyroidism may be associated with increased risks of cardiovascular-related adverse outcomes, bone loss, and cognitive decline 5, 3. Appropriate evaluation includes an investigation of the underlying cause and assessment of an individual's risk factors to determine the necessity and type of treatment that may be recommended 5. Proposed grading systems distinguish between mild and severe subclinical hyperthyroidism and are used alongside patients' age and the presence of risk factors and symptoms to guide treatment 5.