Strategies for improved management of hypothyroidism
Management is clear-cut—yet many patients don’t reach treatment goals. To optimize quality of life, master the fine points of T4 replacement and address the impact of comorbidities.
PRACTICE RECOMMENDATIONS
› Prescribe levothyroxine (LT4) to maintain thyroid-stimulating hormone (TSH) at 4 to 7 mIU/L in select patients with primary hypothyroidism for whom that range of the serum TSH level can be considered appropriate (ie, those older than 65 years and those who have underlying coronary artery disease or another debilitating chronic disorder). A
› Counsel all women of childbearing age with primary hypothyroidism that they need to have their dosage of LT4 increased as soon as pregnancy is suspected. A
› Keep in mind that treating hypothyroidism is not always necessary in older patients who have subclinical disease and a serum TSH level < 10 mIU/L. A
Strength of recommendation (SOR)
A Good-quality patient-oriented evidence
B Inconsistent or limited-quality patient-oriented evidence
C Consensus, usual practice, opinion, disease-oriented evidence, case series
Carpal tunnel syndrome, plantar fasciitis, infertility or miscarriage, dyspepsia, and small intestinal bacterial overgrowth can be associated with hypothyroidism; thyroid function should therefore be assessed in patients who have any of these conditions, along with other signs and symptoms of low thyroid function.8,9 A patient with severe hypothyroidism might present with hemodynamic instability, pericardial or pleural effusion, and myxedema coma.10
Clues in the history and from the lab. A history of radiation to the head, neck, or chest area and a history or family history of autoimmune disorders are risk factors for autoimmune thyroid disease.11,12 Laboratory findings can include markers of oxidative stress, such as elevated levels of low-density lipoprotein cholesterol and serum malondialdehyde.13-15
Screening and diagnosis
Screening. The US Preventive Services Task Force has asserted that evidence is insufficient by which to evaluate the benefits and risks of routine screening for thyroid dysfunction in nonpregnant, asymptomatic adults.16 According to the American Thyroid Association and the American Association of Clinical Endocrinologists, screening should be considered in high-risk patients, including those who take medication that affects thyroid function or the results of thyroid hormone assays (TABLE W2, available at mdedge.com/familymedicine).17-20
Screening inpatients is challenging and usually not recommended unless thyroid disease is strongly suspected. This is because changes in the levels of thyroid hormones, binding proteins, and the TSH concentration can occur in severe nonthyroidal illness; in addition, assay interference by antibodies and other substances can affect thyroid hormone measurement.21
Testing strategy. Generally, screening and diagnosis of hypothyroidism are based primarily on laboratory testing, because signs and symptoms are nonspecific (FIGURE 15). A serum TSH level is usually the initial test when screening for thyroid dysfunction. A normal serum TSH value ranges from 0.5-5.0 mIU/L.
When an abnormal serum TSH level is found, further tests can be performed to investigate, including a serum free thyroxine (FT4) test. (Our preference is to order TSH and FT4 assays simultaneously to facilitate and confirm the diagnosis.) An FT4 test measures the amount of unattached, or free, thyroxine in blood by immunoassay. A normal FT4 value usually ranges from 0.7-1.9 ng/dL.
The combination of a high TSH level and a low FT4 level could be an indication of an underactive thyroid gland (ie, clinical or overt hypothyroidism). Milder, subclinical hypothyroidism is characterized by a higher-than-normal TSH level but a normal FT4 level.22 Central (secondary) hypothyroidism is characterized by a low serum FT4 level and a serum TSH level that can be below the reference range, low normal, or even slightly high.4
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