Hypothyroidism is a common endocrine disorder resulting from deficiency of thyroid hormone. In the United States and other areas of adequate iodine intake, autoimmune thyroid disease (Hashimoto disease) is the most common cause of hypothyroidism; worldwide, iodine deficiency remains the foremost cause.
The image below depicts the hypothalamic-pituitary-thyroid axis.
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ICD-10 codes
These include the following:
Signs and symptoms of hypothyroidism
Hypothyroidism commonly manifests as a slowing in physical and mental activity but may be asymptomatic. Symptoms and signs are often subtle and neither sensitive nor specific.
The following are symptoms of hypothyroidism:
The following are symptoms more specific to Hashimoto thyroiditis:
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Physical signs of hypothyroidism include the following:
Myxedema coma is a severe form of hypothyroidism that most commonly occurs in individuals with undiagnosed or untreated hypothyroidism who are subjected to an external stress. Features are as follows:
See Clinical Presentation for more detail.
Diagnosis of hypothyroidism
Third-generation thyroid-stimulating hormone (TSH) assays are generally the most sensitive screening tool for primary hypothyroidism. [3] If TSH levels are above the reference range, the next step is to measure free thyroxine (T4) or the free thyroxine index (FTI), which serves as a surrogate of the free hormone level. Routine measurement of triiodothyronine (T3) is not recommended.
Biotin, a popular health supplement, may interfere with immunoassays of many hormones, resulting in values that are falsely elevated or suppressed, including for thyroid levels. To avoid misleading test results, the American Thyroid Association recommends cessation of biotin consumption at least 2 days prior to thyroid testing. [4]
Results in patients with hypothyroidism are as follows:
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Abnormalities in the complete blood count (CBC) and metabolic profile that may be found in patients with hypothyroidism include the following [5] :
No universal screening recommendations exist for thyroid disease for adults. The American Thyroid Association recommends screening at age 35 years and every 5 years thereafter, with closer attention to patients who are at high risk, such as the following [7] :
The American College of Obstetricians and Gynecologists (ACOG) does not recommend universal screening for thyroid disease in pregnant women. However, those who are at increased risk warrant screening. These include pregnant women with a personal or family history of thyroid disease, type 1 diabetes, or symptoms suggestive of thyroid disease. There is no proven benefit in screening pregnant women with a mildly enlarged thyroid gland, whereas those with a significant goiter or distinct thyroid nodules require screening. [8]
See Workup for more detail.
Management of hypothyroidism
The treatment goals for hypothyroidism are to reverse clinical progression and correct metabolic derangements, as evidenced by normal blood levels of thyroid-stimulating hormone (TSH) and free thyroxine (T4). Thyroid hormone is administered to supplement or replace endogenous production. In general, hypothyroidism can be adequately treated with a constant daily dose of levothyroxine (LT4).
Significant controversy persists regarding the treatment of patients with mild hypothyroidism. [9] Reviews by the US Preventive Services Task Force [10] and an independent expert panel [11] found inconclusive evidence to recommend aggressive treatment of patients with TSH levels of 4.5-10 mIU/L.
In patients with myxedema coma, an effective approach consists of the following:
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