From the Guidelines
Subclinical hypothyroidism is primarily caused by autoimmune thyroiditis (Hashimoto's disease), but can also result from iodine deficiency, certain medications (like lithium or amiodarone), previous thyroid surgery or radiation, and congenital thyroid disorders. The most common cause of hypothyroidism in the United States is chronic autoimmune (Hashimoto) thyroiditis, as stated in the study by 1. Treatment depends on TSH levels, symptoms, and individual risk factors. For patients with TSH levels above 10 mIU/L, levothyroxine replacement therapy is generally recommended, starting at 25-50 mcg daily for most adults (lower doses of 12.5-25 mcg for elderly or those with heart disease) 1.
Causes of Subclinical Hypothyroidism
- Autoimmune thyroiditis (Hashimoto's disease)
- Iodine deficiency
- Certain medications (like lithium or amiodarone)
- Previous thyroid surgery or radiation
- Congenital thyroid disorders
Treatment Options
For TSH levels between 4.5-10 mIU/L, treatment is considered if symptoms are present, if the patient has positive thyroid antibodies, or has cardiovascular risk factors or is pregnant. The goal is to maintain TSH within normal range (0.4-4.0 mIU/L). Dosage adjustments should be made gradually, checking TSH levels every 6-8 weeks until stabilized, then annually. Once started, treatment is typically lifelong, though some patients may be able to discontinue therapy if the underlying cause resolves. Regular monitoring is essential as both under-treatment and over-treatment can lead to complications, including cardiovascular issues and bone density loss. According to the study by 1, one retrospective cohort study found that levothyroxine use in persons with subclinical hypothyroidism was associated with lower risk for ischemic heart disease events and overall mortality.
Key Considerations
- TSH levels above 10 mIU/L require levothyroxine replacement therapy
- TSH levels between 4.5-10 mIU/L require treatment if symptoms are present or if the patient has positive thyroid antibodies or cardiovascular risk factors
- Regular monitoring is essential to avoid complications
- Treatment is typically lifelong, but may be discontinued if the underlying cause resolves, as noted in the study by 1.
From the FDA Drug Label
Maternal hypothyroidism during pregnancy is associated with a higher rate of complications, including spontaneous abortion, gestational hypertension, pre‑eclampsia, stillbirth, and premature delivery. Untreated maternal hypothyroidism may have an adverse effect on fetal neurocognitive development
The causes of subclinical hypothyroidism are not directly stated in the provided drug label. However, it mentions that maternal hypothyroidism can have adverse effects on fetal development and pregnancy outcomes.
- Hypothyroidism can be caused by various factors, but the label does not explicitly state the causes of subclinical hypothyroidism. As for treatment options, the label mentions levothyroxine sodium as a replacement therapy for hypothyroidism, including primary, secondary, and tertiary congenital or acquired hypothyroidism 2.
- The label recommends monitoring TSH levels and adjusting the levothyroxine sodium dosage during pregnancy and the postpartum period.
- It also states that levothyroxine sodium should not be discontinued during pregnancy and that hypothyroidism diagnosed during pregnancy should be promptly treated.
From the Research
Causes of Subclinical Hypothyroidism
- Subclinical hypothyroidism is most often caused by autoimmune (Hashimoto) thyroiditis 3
- Serum thyrotropin levels rise as people without thyroid disease age, which may lead to an overestimation of the true prevalence of subclinical hypothyroidism in persons older than 70 years 3
- Iodine deficiency is also a common cause of hypothyroidism worldwide, although this is more relevant to overt hypothyroidism 4
- Other causes of hypothyroidism, such as chronic autoimmune thyroiditis, drugs (e.g. amiodarone, lithium, and immune checkpoint inhibitors), radioactive-iodine treatment, and thyroid surgery, may also contribute to subclinical hypothyroidism 5
- Small amounts of supplementary iodine can cause slight but significant changes in thyroid hormone function in predisposed individuals, potentially leading to subclinical hypothyroidism 6
Treatment Options for Subclinical Hypothyroidism
- Levothyroxine therapy may be indicated for patients with subclinical hypothyroidism and serum thyrotropin levels of 10 mU/L or higher, or for young and middle-aged individuals with subclinical hypothyroidism and symptoms consistent with mild hypothyroidism 3
- However, levothyroxine therapy may be associated with iatrogenic thyrotoxicosis, especially in elderly patients, and there is no evidence that it is beneficial in persons aged 65 years or older 3
- The rationale for treatment is based on the potential for decreasing the risk of adverse cardiovascular events and the possibility of preventing progression to overt hypothyroidism 3
- In patients with grade 1 subclinical hypothyroidism, it is reasonable to refrain from immediate levothyroxine treatment if they are closely monitored, except in women who are pregnant or in progressive cases 7