From the Guidelines
Subclinical hypothyroidism is characterized by elevated thyroid stimulating hormone (TSH) levels with normal thyroid hormone levels, resulting from mild thyroid gland dysfunction and compensatory mechanisms to maintain normal circulating thyroid hormone levels. The pathophysiology of subclinical hypothyroidism involves the pituitary gland increasing TSH production through negative feedback mechanisms to stimulate the thyroid gland to produce more hormones, as seen in individuals with elevated serum TSH concentrations 1. Common causes of subclinical hypothyroidism include:
- Hashimoto's thyroiditis, an autoimmune condition where antibodies attack thyroid tissue
- Iodine deficiency
- Certain medications, such as lithium or amiodarone
- Previous thyroid surgery or radiation
- Genetic factors Some key points to note about subclinical hypothyroidism include:
- Approximately 2% to 5% of patients with subclinical hypothyroidism progress to overt hypothyroidism annually, with a higher rate of progression in individuals with higher baseline serum TSH concentrations and those with antithyroid antibodies 1
- In some cases, individuals with hypothyroid symptoms and high TSH (>10 mIU/L) with low normal FT4 have been defined as having overt hypothyroidism 1
- The subtle thyroid dysfunction can affect multiple body systems, potentially causing mild symptoms like fatigue, cold intolerance, or mild cognitive changes, though many patients remain asymptomatic.
From the FDA Drug Label
The FDA drug label does not answer the question.
From the Research
Definition and Classification of Subclinical Hypothyroidism
- Subclinical hypothyroidism (SCH) is defined as elevated thyroid stimulating hormone (TSH) with normal levels of free triiodothyronine (FT3) and free thyroxine (FT4) 2, 3, 4, 5.
- SCH is further classified into a milder condition with TSH levels between 4.0 and 10.0 milli-international units (mIU)/l (mild-SCH) and a severe form with TSH >10.0 mIU/l (severe-SCH) 2, 4.
Pathophysiology and Risks Associated with Subclinical Hypothyroidism
- Elevated TSH levels in patients with subclinical hypothyroidism do not reflect pituitary compensation to maintain euthyroidism but probably represent a state of mild tissue hypothyroidism 3.
- SCH is associated with the risk of progression to overt hypothyroidism and with the risk of neuropsychiatric effects 3.
- Subclinical hypothyroidism may be associated with an increased risk of heart failure, coronary artery disease events, and mortality from coronary heart disease 5.
- Middle-aged patients with subclinical hypothyroidism may have cognitive impairment, nonspecific symptoms such as fatigue, and altered mood 5.
Diagnosis and Management of Subclinical Hypothyroidism
- The diagnosis of hypothyroidism is primarily based on clinical signs and symptoms as well as measurement of thyroid-stimulating hormone (TSH) concentration 6.
- Treatment of patients with subclinical hypothyroidism is still a controversial topic, and the decision to treat should be individualized based on factors such as patient age, presence of pregnancy or comorbidities, and serum TSH levels 2, 6, 4, 5.
- Levothyroxine therapy is clearly indicated if the TSH concentration is >10 mU/l, but for lower TSH values, the decision for therapy should be individualized 2, 6, 4, 5.