Which Product Is Ideal for You?

Summary

Epidemiology: hypothyroidism is more common after age 65 yr and in women; risk is elevated among residents of skilled nursing facilities; risk factors include previous irradiation or surgery involving the thyroid, family history of thyroid disease, recent pregnancy, Turner syndrome, and presence of other autoimmune conditions

Signs and symptoms: generally nonspecific, with few pathognomonic signs; common symptoms — include fatigue, difficulty concentrating, weight gain, dry skin, depression, intolerance of cold, and hair loss, especially in the outer third of the eyebrows (pathognomonic for hypothyroidism); women may experience menorrhagia, amenorrhea, or irregular periods; patients with thyroiditis may have discomfort or pain over the lower neck and a diffusely enlarged thyroid; goiter is more common with severe disease and in longstanding hypothyroidism; goiter is also common in patients with Riedel struma, most of whom are euthyroid; common physical findings — include bradycardia and low blood pressure (BP); general hair loss and nonpitting peripheral edema are possible; physical examination is typically normal, other than vital signs

Evaluation: levels of thyrotropin (TSH), free triiodothyronine (T3), and thyroxine (T4) levels are key; an elevated TSH level with low T4 or T3 level is overt hypothyroidism; mildly elevated TSH with normal T4 and T3 is subclinical hypothyroidism; TSH is elevated in patients with primary hypothyroidism but low in secondary hypothyroidism; peroxidase antibody titers may help identify Hashimoto thyroiditis but have little or no value in treatment or prognosis; there is no role for imaging unless nodules are present; in cases of secondary hypothyroidism, assess for other pituitary abnormalities

Hashimoto thyroiditis: the most common type of thyroiditis that leads to permanent, overt long-term hypothyroidism; autoimmune thyroiditis that progresses slowly over time; symptoms manifest when patients are in their late 30s or 40s; typically, patients do not seek care until thyroid function is significantly impaired; exacerbated by iodine supplements and foods high in iodine

Hypothyroidism secondary to acute thyroiditis: eg, DeQuervain thyroiditis; patients may become transiently hyperthyroid due to the release of existing thyroid hormone stored in the gland; subsequently, levels usually decrease to a euthyroid or hypothyroid state lasting a few weeks to months (permanent in 10% patients)

Iatrogenic disease: secondary to irradiation or surgery for Graves disease, Riedel struma, or chronic fibrocytic thyroiditis (associated with large, nontender goiter)

Other causes: include medications (eg, amiodarone, lithium, interferon alpha), infiltrative disorders (amyloidosis or sarcoidosis), or iodine insufficiency

Congenital hypothyroidism (CH): usually caused by agenesis or hypoplasia of the thyroid gland; also caused by ingestion of antithyroid medications by mothers early in pregnancy, particularly methimazole; propylthiouracil does not cross the blood-placenta barrier; signs in infants include large, thick tongues, abnormally enlarged fontanelles, delayed closure of the posterior fontanelle, hoarse cry, abdominal distention, difficulty feeding, constipation, poor muscle tone, and persistent newborn jaundice; infants may be deficient in several pituitary hormones; hypopituitarism should be suspected in infants with issues maintaining blood glucose, persistent hyperbilirubinemia, or micropenis

Treatment: L-thyroxine is used for replacement; the typical daily requirement for a patient with complete absence of thyroid function is between 113 and 137 µg; for older patients or those at risk for or having existing heart disease, start with 25 to 50 µg, then increase by 25 µg every 4 to 6 wk, based on TSH levels; patients with mild thyroid dysfunction typically require 50 to 100 µg and annual surveillance; a study by Dong BJ et al (1997) showed similar efficacy of generic and brand-name formulations

Desiccated thyroid (Armour Thyroid) vs purified thyroid: desiccated thyroid is ground and dried animal thyroid tissue; contains all thyroid components; safe to prescribe but has no advantage over L-thyroxine for most patients

Missed doses: in a study of ≈50 patients, the investigators compared daily dosing vs 7 times the daily dose once weekly; daily measurements of metabolic indicators of thyroid function showed no differences between groups; findings suggest catch-up doses are not harmful

Treatment using T3: some studies have shown that, among patients >65 yr of age exhibiting neurocognitive deficits despite euthyroid replacement of thyroid hormone, 12.5 µg of T3 with a concomitant 50-µg reduction in the T4 dose may be beneficial; in studies of patients <45 yr of age, supplemental T3 was not associated with cognitive benefits

Monitoring thyroid hormone levels: 97% of T4 and 99.7% of T3 is protein bound; changes in serum protein levels require changes in dosage to maintain free T4 and T3 levels; starvation for weight loss or related to chemotherapy, malnutrition, or nephrotic syndrome require reduced doses; patients who are pregnant or initiate estrogen therapy may require increased doses; pregnant women — need close monitoring throughout gestation; replacement requirements may increase 25% to 50%; L-thyroxine should not be taken within ≈4 hr of taking iron or prenatal vitamins because iron and calcium decrease absorption

Treatment of CH: L-thyroxine is crushed and mixed with formula or breast milk at a dose of 10 to 15 µg/kg per day; thyroid medication should not be mixed with soy-based formula because soy proteins combine with thyroxine and reduce absorption levels

Subacute hypothyroidism: common in older adults, women, and persons of European ancestry; over time, there is a low risk for progression to overt hypothyroidism (≈5% over a 3-yr period); patients with TSH levels >10 mIU/mL and those with positive antithyroid antibodies are at higher risk; treatment is not recommended unless patients become symptomatic; follow up annually with TSH and T4 levels to monitor for progression; Leiden 85-plus Study — compared euthyroid individuals with patients who had subclinical hypothyroidism; no differences were found in decline in cognitive function, need for support in activities of daily living, or development of other clinical problems; patients with subclinical hypothyroidism had a lower mortality rate over the next 5 yr

Complications of hypothyroidism: associated with elevated lipid levels, including the low-density lipoproteins, which increase risk for heart disease; severe hypothyroidism can lead to myxedema, myxedema coma, and neuropsychiatric problems, such as depression and confusion; CH can result in severe and irreversible intellectual disability if not recognized early in life; however, because of universal screening in most developed countries, this is now uncommon

Recommendations for screening: in 2015, the US Preventive Services Task Force reaffirmed their previous recommendation against routine screening for thyroid disease in healthy adults; this is consistent with the 2004 jointly issued guidelines from the American Thyroid Association, the American Association of Clinical Endocrinologists, and the Endocrine Society