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Hypothyroidism

Definition
Hypothyroidism is a chronic endocrine disease associated with the deficiency of thyroxine and T3 thyroid hormones.
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Pathophysiology
Hypothyroidism is most frequently caused by a failure of the thyroid gland to produce thyroid hormones (99%). Other causes include the underproduction of TSH by the pituitary gland and deficiency of the thyrotropin-releasing hormone.
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Epidemiology
The prevalence of overt and subclinical hypothyroidism in the US is estimated at 300 per 100,000 population and 4,300 per 100,000 population, respectively. Hypothyroidism is 2-8 times more prevalent in women than men, and it's prevalence increases with age.
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Disease course
Clinical manifestations include weight gain, fatigue, proximal weakness, decreased concentration, depression, diffuse muscle pain, menstrual irregularities, constipation, dry skin, hair loss, and sensory neuropathy. A severe form of hypothyroidism-myxedema coma- presents with altered mental status, hypothermia, hyponatremia and bradycardia. The disease decreases productivity and QoL.
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Prognosis and risk of recurrence
Hypothyroidism is not associated with an increase in mortality. Treatment is well tolerated and results in improved QoL in most patients. However, untreated hypothyroidism leads to disease progression and ultimately, coma and death.
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Key sources
The following summarized guidelines for the evaluation and management of hypothyroidism are prepared by our editorial team based on guidelines from the Endocrine Society (ES 2020), the American College of Obstetricians and Gynecologists (ACOG 2020), the American Heart Association (AHA/HRS/ACC 2019), the American Thyroid Association (ATA 2017), and the American Thyroid Association (ATA/AACE 2012).
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Guidelines

1.Screening and diagnosis

Clinical scoring systems: avoid using clinical scoring systems to diagnose hypothyroidism.
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  • Indications for screening

  • Indications for testing (dyslipidemia)

  • Indications for testing (infertility)

2.Diagnostic investigations

Anti-TPO antibodies: measure anti-TPO antibodies in the evaluation of patients with subclinical hypothyroidism.
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  • Thyroid hormone tests

  • Other diagnostic tests

3.Medical management

Indications for L-thyroxine, abnormal thyroid-stimulating hormone
Consider initiating levothyroxine in patients with serum TSH levels > 10 mIU/L, as these patients are at increased risk for HF and cardiovascular mortality.
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Consider initiating treatment based on individual factors in patients with TSH levels between the upper limit of a given laboratory's reference range and 10 mIU/L, particularly if patients have symptoms suggestive of hypothyroidism, positive anti-TPO antibodies, or evidence of ASCVD, HF, or associated risk factors for these diseases.
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  • Indications for L-thyroxine (normal TSH)

  • Choice of agent

  • Initial L-thyroxine dose

  • Treatment targets

  • Management of dyslipidemia

4.Nonpharmacologic interventions

Iodine supplementation: do not use iodine supplementation, including kelp or other iodine-containing functional foods, in the management of hypothyroidism in iodine-sufficient areas.
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  • Selenium supplementation

5.Specific circumstances

Pregnant patients, screening
Do not obtain universal screening for thyroid disease in pregnancy because identification and treatment of maternal subclinical hypothyroidism has not been shown to result in improved pregnancy outcomes and neurocognitive function in offspring.
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Obtain TSH as a first-line screening test to assess thyroid status if indicated.
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  • Pregnant patients (testing)

  • Pregnant patients (management)

  • Pregnant patients (monitoring)

  • Patients with combined adrenal insufficiency

  • Patients with conduction disorders

6.Patient education

Timing of L-thyroxine doses: advise levothyroxine to be taken with water consistently 30-60 minutes before breakfast, or at bedtime, 4 hours after the last meal.
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  • Nutraceuticals for hypothyroidism

7.Follow-up and surveillance

Indications for specialist referral: manage most patients with primary hypothyroidism by non-endocrinologist physicians familiar with the diagnosis and treatment of hypothyroidism. Refer patients with hypothyroidism meeting any of the following criteria for a consultation with an endocrinologist:
infant and pediatric patients
female patient planning conception
pregnant patients
patients difficult to render and maintain in a euthyroid state
cardiac disease
presence of goiter, nodule, or other structural changes in the thyroid gland
presence of other endocrine diseases, such as adrenal or pituitary disorders
unusual constellation of thyroid function test results
unusual causes of hypothyroidism, such as induced by agents interfering with the absorption of levothyroxine, impacting thyroid gland hormone production or secretion, affecting the hypothalamic-pituitary-thyroid axis (directly or indirectly), increasing clearance, or peripherally impacting metabolism
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