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
Causes of subclinical hypothyroidism are the same as those of overt hypothyroidism, and include Hashimoto disease. The combination of an elevated TSH level and a normal FT4 level is associated with disorders characterized by protein-binding variations (eg, pregnancy, genetic disorders, drugs), TSH-secreting pituitary adenoma, class II and III obesity (respectively, body mass index, ≥ 35 but < 40 and ≥ 40), and assay variability.49,51
Lab diagnosis: Fraught with difficulty
The serum TSH level and either the total T4 level or the FT4 level should be measured to make a diagnosis of subclinical hypothyroidism. Most laboratories use a 1-step analogue immunoassay to determine free thyroid hormones; protein-binding variations can thus affect measurement of FT4.
Several scenarios that can result in inaccurate measurement of FT4 by radioimmunoassay include genetic disorders that affect binding proteins; pregnancy; use of certain drugs, including heparin, furosemide, antiepileptic agents, salicylate, ferrous sulfate, and cholesterol-binding resins; and some medical conditions, including cardiac surgery, critical illness, and renal failure. Variables that inhibit proper production of thyroid hormones—stress, infection, fluoride (an iodine antagonist), toxins (pesticides, mercury, cadmium, lead) and autoimmune conditions, such as celiac disease—should be considered when attempting to determine the cause of subclinical hypothyroidism.
Liquid chromatography–mass spectrometry measurement of thyroid hormones might be more accurate than immunoassay.53 Measuring serum total T4 and FT4 by dialysis, free from interfering proteins, might also be useful when measurement of FT4 by immunoassay is affected by binding-protein variations.
Features of subclinical hypothyroidism
Most patients who have subclinical hypothyroidism and a serum TSH level < 10 mIU/L are asymptomatic. Some might have nonspecific symptoms of hypothyroidism, however, such as reduced quality of life, poor cognitive function, and poor memory—symptoms that do not typically correlate with the serum TSH level.
It has been suggested that some elderly people normally have a higher level of serum TSH, and that they might have even a prolonged lifespan.51 Additionally, it has been shown that, in nonpregnant adult patients with subclinical hypothyroidism and a serum TSH level of 4.5 to 10 mIU/L, treatment with LT4 was not associated with improvement in thyroid-related symptoms or general quality of life.52
Treat, or don't treat, subclinical hypothyroidism?
It is well accepted that the goal of therapy in hypothyroid patients is to normalize the serum TSH level; however, the American Thyroid Association and the American Association of Clinical Endocrinology recommend starting LT4 in patients with a serum TSH level ≥ 10 mIU/L (TABLE 5).59-62 The principal reason for not treating subclinical hypothyroidism is the lack of benefit in reducing the risk of cardiovascular morbidity and mortality when the TSH level is between 7.5 and 10 mIU/L.62
Continue to: Routine treatment
