Hypothyroidism
Author: Shikha Bharaktiya, MD, Clinical Fellow, Department of Internal Medicine, Division of Endocrinology and Metabolism, University of Texas Medical School at Houston
Coauthor(s): Philip R Orlander, MD, Interim Chair of Medicine, Director of Endocrinology and Metabolism Fellowship, Director and Professor, Department of Medicine, Division of Endocrinology, University of Texas Health Science Center at Houston; Walter R Woodhouse, MD, MSA, Associate Clinical Professor, Department of Family Practice, Medical College of Ohio; Anu Bhalla Davis, MD, Assistant Professor, Department of Internal Medicine, Division of Diabetes, Endocrinology, and Metabolism, University of Texas Medical School at Houston
Contributor Information and Disclosures
Updated: Mar 31, 2010
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Introduction
Background
Hypothyroidism is a common endocrine disorder resulting from deficiency of thyroid hormone. It usually is a primary process in which the thyroid gland produces insufficient amounts of thyroid hormone. It can also be secondary—that is, lack of thyroid hormone secretion due to inadequate secretion of either thyrotropin (ie, thyroid-stimulating hormone [TSH]) from the pituitary gland or thyrotropin-releasing hormone (TRH) from the hypothalamus (secondary or tertiary hypothyroidism). The patient's presentation may vary from asymptomatic to, rarely, coma with multisystem organ failure (myxedema coma). The most common cause in the Unites States is autoimmune thyroid disease (Hashimoto thyroiditis).
Cretinism refers to congenital hypothyroidism, which affects 1 per 4000 newborns.
Subclinical hypothyroidism, also referred to as mild hypothyroidism, is defined as normal serum free T4 levels with slightly high serum TSH concentration.
Recent studies
In a 12-year longitudinal study, Stuckey et al investigated the long-term risk of hypothyroidism in women who previously had had postpartum thyroid dysfunction (PPTD). The study involved 409 women, 71 of whom had previously been diagnosed with PPTD. At 12-year follow-up, 27 women in the PPTD group and 14 women in the non-PPTD group (38% and 4%, respectively) were found to have hypothyroidism. Based on an analysis of odds ratios (ORs), the authors concluded that within the PPTD group, women who had been diagnosed with postpartum hypothyroidism were among those at particularly high long-term risk for hypothyroidism (OR = 9.7).1
Pathophysiology
Localized disease of the thyroid gland that results in decreased thyroid hormone production is the most common cause of hypothyroidism. Under normal circumstances, the thyroid releases 100-125 nmol of thyroxine (T4) daily and only small amounts of triiodothyronine (T3). The half-life of T4 is approximately 7-10 days. T4, a prohormone, is converted to T3, the active form of thyroid hormone, in the peripheral tissues by 5’-deiodination. Early in the disease process, compensatory mechanisms maintain T3 levels. Decreased production of T4 causes an increase in the secretion of TSH by the pituitary gland. TSH stimulates hypertrophy and hyperplasia of the thyroid gland and thyroid T4-5'-deiodinase activity. This, in turn, causes the thyroid to release more T3.
Because all metabolically active cells require thyroid hormone, deficiency of the hormone has a wide range of effects. Systemic effects are due to either derangements in metabolic processes or direct effects by myxedematous infiltration (ie, accumulation of glucosaminoglycans in the tissues).
The myxedematous changes in the heart result in decreased contractility, cardiac enlargement, pericardial effusion, decreased pulse, and decreased cardiac output. In the GI tract, achlorhydria and decreased intestinal transit with gastric stasis can occur. Delayed puberty, anovulation, menstrual irregularities, and infertility are common. Decreased thyroid hormone effect can cause increased levels of total cholesterol and low-density lipoprotein (LDL) cholesterol and a possible change in high-density lipoprotein (HDL) cholesterol due to a change in metabolic clearance. In addition, hypothyroidism may result in an increase in insulin resistance.
Frequency
United States
The National Health and Nutrition Examination Survey (NHANES 1999-2002) of 4,392 individuals reflecting the US population reported hypothyroidism (defined as TSH levels >4.5 mIU/L) in 3.7% of the population.2 Hypothyroidism is more common in women with small body size at birth and low body mass index during childhood.3
International
Iodine deficiency as a cause of hypothyroidism is more common internationally. The prevalence is reported as 2-5% depending on the study, increasing to 15% by age 75 years.
Mortality/Morbidity
In developed countries, death caused by hypothyroidism is uncommon.
Race
NHANES 1999-2002 reported that the prevalence of hypothyroidism (including subclinical) was higher in whites (5.1%) and Mexican Americans than in African Americans (1.7%). African Americans tend to have lower TSH values.2
Sex
Community studies use slightly different criteria for determining hypothyroidism; therefore, female-to-male ratios vary. Generally, thyroid disease is much more common in females than in males, with reports of prevalence 2-8 times higher in females.
Age
The frequency of hypothyroidism, goiters, and thyroid nodules increases with age. Hypothyroidism is most prevalent in elderly populations, with 2% to as much as 20% of older age groups having some form of hypothyroidism. The Framingham study found hypothyroidism (TSH >10 mIU/L) in 5.9% of women and 2.4% of men older than 60 years.4 In NHANES 1999-2002, the odds of having hypothyroidism were 5 times greater in persons aged 80 years and older than in individuals aged 12-49 years.2
Clinical
History
Hypothyroidism commonly manifests as a slowing in physical and mental activity but may be asymptomatic. Symptoms and signs of this disease are often subtle and neither sensitive nor specific. Classic signs and symptoms, such as cold intolerance, puffiness, decreased sweating, and coarse skin, previously reported in 90-97% of patients, may actually occur in only 50-64% of younger patients. Many of the more common symptoms are nonspecific and difficult to attribute to a specific cause. Individuals can also present with obstructive sleep apnea (secondary to macroglossia) or carpal tunnel syndrome. Women can present with galactorrhea and menstrual disturbances. Consequently, the diagnosis of hypothyroidism is based on clinical suspicion and confirmed by laboratory testing.
Myxedema coma is a severe form of hypothyroidism that results in an altered mental status, hypothermia, bradycardia, hypercarbia, and hyponatremia. Cardiomegaly, pericardial effusion, cardiogenic shock, and ascites may be present. Myxedema coma most commonly occurs in individuals with undiagnosed or untreated hypothyroidism who are subjected to an external stress, such as low temperature, infection, or medical intervention (eg, surgery or hypnotic drugs).
The following are symptoms of hypothyroidism:
* Fatigue, loss of energy, lethargy
* Weight gain
* Decreased appetite
* Cold intolerance
* Dry skin
* Hair loss
* Sleepiness
* Muscle pain, joint pain, weakness in the extremities
* Depression
* Emotional lability, mental impairment
* Forgetfulness, impaired memory, inability to concentrate
* Constipation
* Menstrual disturbances, impaired fertility
* Decreased perspiration
* Paresthesia and nerve entrapment syndromes
* Blurred vision
* Decreased hearing
* Fullness in the throat, hoarseness
The following are symptoms more specific to Hashimoto thyroiditis:
* Feeling of fullness in the throat
* Painless thyroid enlargement
* Exhaustion
* Neck pain, sore throat, or both
* Low-grade fever
Physical
Signs found in hypothyroidism are usually subtle, and their detection requires a careful physical examination. Moreover, they are often dismissed as part of aging; however, clinicians should consider a diagnosis of hypothyroidism when such signs are present.
Physical signs of hypothyroidism include the following:
* Hypothermia
* Weight gain
* Slowed speech and movements
* Dry skin
* Jaundice
* Pallor
* Coarse, brittle, strawlike hair
* Loss of scalp hair, axillary hair, pubic hair, or a combination
* Dull facial expression
* Coarse facial features
* Periorbital puffiness
* Macroglossia
* Goiter
* Hoarseness
* Decreased systolic blood pressure and increased diastolic blood pressure
* Bradycardia
* Pericardial effusion
* Abdominal distension, ascites (uncommon)
* Nonpitting edema (myxedema)
* Pitting edema of lower extremities
* Hyporeflexia with delayed relaxation, ataxia, or both
Additional signs specific to different causes of hypothyroidism, such as diffuse or nodular goiter or pituitary tumor, can occur.
Metabolic abnormalities associated with hypothyroidism include anemia, dilutional hyponatremia, hyperlipidemia, and reversible increase in creatinine.5
Causes
Worldwide, iodine deficiency remains the foremost cause of hypothyroidism. In the United States and other areas of adequate iodine intake, autoimmune thyroid disease is most common. The prevalence of antibodies is higher in women, and increases with age.
Primary hypothyroidism
* Autoimmune: The most frequent cause of acquired hypothyroidism is autoimmune thyroiditis (Hashimoto thyroiditis). The body recognizes the thyroid antigens as foreign, and a chronic immune reaction ensues, resulting in lymphocytic infiltration of the gland and progressive destruction of functional thyroid tissue. Up to 95% of affected individuals have circulating antibodies to thyroid tissue. Antimicrosomal or antithyroid peroxidase (anti-TPO) antibodies are found more commonly than antithyroglobulin antibodies (95% vs 60%). These antibodies may not be present early in the disease process and usually disappear over time.6
* Postpartum thyroiditis: Up to 10% of postpartum women may develop lymphocytic thyroiditis in the 2-10 months after delivery. The frequency may be as high as 25% in women with type 1 diabetes mellitus. The condition is usually transient (2-4 mo) and can require a short course of treatment with levothyroxine (LT4), but postpartum patients with lymphocytic thyroiditis are at increased risk of permanent hypothyroidism. The hypothyroid state can be preceded by a short thyrotoxic state. High titers of anti-TPO antibodies during pregnancy have been reported to be 97% sensitive and 91% specific for postpartum autoimmune thyroid disease.
* Subacute granulomatous thyroiditis: Inflammatory conditions or viral syndromes may be associated with transient hyperthyroidism followed by transient hypothyroidism (de Quervain or painful thyroiditis, subacute thyroiditis). These are often associated with fever, malaise, and a painful and tender gland.
* Drugs: Medications such as amiodarone, interferon alpha, thalidomide, lithium, and stavudine have also been associated with primary hypothyroidism.
* Iatrogenic
o Use of radioactive iodine for treatment of Graves disease generally results in permanent hypothyroidism within 1 year after therapy. The frequency is much lower in patients with toxic nodular goiters and those with autonomously functioning thyroid nodules. Patients treated with radioiodine should be monitored for clinical and biochemical evidence of hypothyroidism.
o Thyroidectomy
o External neck irradiation (for head and neck neoplasms, breast cancer, or Hodgkin disease) may result in hypothyroidism; patients who have received these treatments require monitoring of thyroid function.
* Rare: Rare causes include inborn errors of thyroid hormone synthesis.
* Iodine deficiency or excess: Worldwide, iodine deficiency is the most common cause of hypothyroidism. Excess iodine, as in radiocontrast dyes, amiodarone, health tonics, and seaweed, inhibits iodide organification and thyroid hormone synthesis. Most healthy individuals have a physiologic escape from this effect; however those with abnormal thyroid glands may not. These include patients with autoimmune thyroiditis, surgically treated Graves hyperthyroidism (subtotal thyroidectomy) and prior radioiodine therapy.7
Central hypothyroidism
Central hypothyroidism (secondary or tertiary) results when the hypothalamic-pituitary axis is damaged. Various causes should be considered8,9 :
* Pituitary adenoma
* Tumors impinging on the hypothalamus
* History of brain irradiation
* Drugs (eg, dopamine, lithium)
* Sheehan syndrome
* Genetic disordersDifferential Diagnoses
Addison Disease
Infectious Mononucleosis
Anovulation
Infertility
Apnea, Sleep
Infertility, Male
Autoimmune Thyroid Disease and Pregnancy
Iodine Deficiency
Cardiac Tamponade
Lithium Nephropathy
Chronic Fatigue Syndrome
Lymphomas, Endocrine, Mesenchymal, and Other Rare Tumors of the Mediastinum
Constipation
Megacolon, Chronic
Craniopharyngiomas
Menopause
De Quervain Thyroiditis
Myxedema Coma or Crisis
Depression
Obesity
Dysmenorrhea
Ovarian Insufficiency
Eosinophilia
Pericardial Effusion
Eosinophilia-Myalgia Syndrome
Pituitary Macroadenomas
Erectile Dysfunction
Polyglandular Autoimmune Syndrome, Type I
Euthyroid Sick Syndrome
Polyglandular Autoimmune Syndrome, Type II
Fibromyalgia
Polyglandular Autoimmune Syndrome, Type III
Goiter
Prolactin Deficiency
Goiter, Lithium-Induced
Riedel Thyroiditis
Goiter, Nontoxic
Sleep Disorder, Geriatric
Hypercholesterolemia, Familial
Sleep Disorders
Hypercholesterolemia, Polygenic
Syndrome of Inappropriate Secretion of Antidiuretic Hormone
Hypoalbuminemia
Thyroid Lymphoma
Hypochondriasis
Thyroiditis, Subacute
Hypopituitarism (Panhypopituitarism)
Thyroxine-Binding Globulin Deficiency
Hypothermia
Ileus
Other Problems to Be Considered
The list of differential diagnoses for hypothyroidism is long because the most frequent presenting symptoms are nonspecific.
Workup
Laboratory Studies
Third-generation TSH assays are readily available and are generally the most sensitive screening tool for primary hypothyroidism.
The generally accepted reference range for normal serum TSH is 0.40-4.2 mIU/L. In NHANES III (1988-1994), of 17,353 people evaluated, 80.8% had a serum TSH below 2.5 mIU/L; TSH concentrations rose with advancing age.10
TSH levels peak in the evening and are lowest in the afternoon, with marked variations due to physiologic conditions such as illness, psychiatric disorders, and low energy intake.
If TSH levels are above the reference range, the next step would be to measure total T4 with a measure of binding proteins. Thyroxine is highly protein bound (99.97%) with approximately 85% bound to thyroid-binding globulin (TBG), approximately 10% bound to transthyretin or thyroid-binding prealbumin, and the remainder bound loosely to albumin.
The levels of these binding proteins can vary by hormonal status, inheritance, and in various disease states. Hence, free T4 assays are becoming popular as they measure unbound (ie, free hormone). However, free T4 assays can be unreliable in the setting of severe illness. No currently available kit actually measures unbound T4 directly. Free thyroid hormone levels can be estimated by calculating the percentage of available thyroid hormone-binding sites (T3 resin uptake) or by measuring the concentration of TBG. A free thyroxine index (FTI) serves as a surrogate of the free hormone level. The FTI is the product of the T3 resin uptake and total T4 levels.
Patients with primary hypothyroidism have elevated TSH levels and decreased free hormone levels. Patients with elevated TSH levels but normal free hormone levels or estimates are considered to have mild or subclinical hypothyroidism.
Primary hypothyroidism is virtually the only disease that is characterized by sustained, rising TSH levels. As the TSH level increases early in the disease, an increased conversion of T4 to T3 occur, this maintains T3 levels. In early hypothyroidism, TSH levels are increased, T4 levels are normal to low, and T3 levels are normal.
Evaluation of the presence of thyroid autoantibodies (antimicrosomal or anti-TPO antibodies) and antithyroglobulin (anti-Tg) may be helpful in determining the etiology of hypothyroidism or in predicting future hypothyroidism. In addition, anti-TPO antibodies have been associated with a higher risk of infertility and miscarriage.
In patients with nonthyroid disease who are severely ill, TSH secretion is normal or decreased, total T4 levels are decreased, and total T3 levels are markedly decreased. This can be confused with secondary hypothyroidism. In these patients, the primary abnormality is the decreased peripheral production of T3 from T4. They have an increased reverse T3, which can be measured. Other abnormalities seen in patients who are critically ill include decreased TBG levels and abnormalities in the hypothalamic-pituitary axis. During recovery, some patients have transient elevations in serum TSH concentrations (up to 20 mIU/L). Hence, thyroid function should not be evaluated in a critically ill person unless thyroid dysfunction is strongly suspected, and, if so, screening with TSH alone is insufficient.
In patients with hypothalamic or pituitary dysfunction, TSH levels do not increase in appropriate relation to the low free T4 levels. The absolute levels may be in the normal or even slightly elevated range but inappropriately low for the severity of the hypothyroid state. Hence, when secondary or tertiary hypothyroidism is suspected, a serum TSH measurement alone is inadequate; a free T4 should be measured.
The TRH stimulation test is rarely needed currently because of improved TSH assays.
Imaging Studies
Ultrasonographic scanning of the neck and thyroid can be used to detect nodules and infiltrative disease. It has little use in hypothyroidism per se unless a secondary anatomic lesion in the gland is of clinical concern. Hashimoto thyroiditis is usually associated with a heterogeneous ultrasonographic image. It can be rarely associated with lymphoma of the thyroid. Serial images with fine-needle aspiration of suspicious nodules may be useful.
Radioactive iodine uptake (RAIU) and thyroid scanning are not useful in hypothyroidism because these tests require some level of endogenous function in the hypofunctioning gland to provide information. Patients with Hashimoto thyroiditis may have relatively high early uptake (after 4 h) but do not have the usual doubling of uptake at 24 hours consistent with an organification defect.
Patients undergoing whole-body F18-fluorodeoxyglucose positron emission tomography (FDG-PET) for nonthyroid disease often show significant thyroid uptake as an incidental finding.11 In general, diffuse uptake by the thyroid on FDG-PET is considered a benign finding and is typical of thyroiditis and/or hypothyroidism.
Procedures
Fine-needle aspiration biopsy
Thyroid nodules are often found incidentally during physical examination, chest radiograph, CT scan, or MRI. Thyroid nodules can be found in patients who are hypothyroid, euthyroid, or hyperthyroid. Fine-needle aspiration (FNA) biopsy is the procedure of choice to evaluate suspicious nodules.
About 5-6% of solitary nodules are malignant. Suspicious nodules are those that are larger than 1 cm in diameter or those with suspicious features found on a sonogram (eg, irregular margins, intranodular vascular spots, microcalcifications).
Risk factors for thyroid nodules include age greater than 60 years, history of head or neck irradiation, or family history of thyroid cancer.
Histologic Findings
Autoimmune thyroiditis causes a decrease in intrathyroidal iodine stores, an increased iodine turnover, and defective organification. Chronic inflammation of the gland causes progressive destruction of the functional tissue with widespread infiltration by lymphocytes and plasma cells with epithelial cell abnormalities. In time, dense fibrosis and atrophic thyroid follicles replace the initial lymphocytic hyperplasia and vacuoles. Functional tissue destruction and infiltration may also be caused by previous administration of radioiodine, surgical fibrosis, metastasis, lymphomatous changes, sarcoidosis, tuberculosis, amyloidosis, cystinosis, thalassemia, and Riedel thyroiditis.Treatment
Medical Care
The treatment goals for hypothyroidism are the reversal of clinical progression and the corrections of metabolic derangements as evidenced by normal blood levels of TSH and free 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).
Clinical benefits begin in 3-5 days and level off after 4-6 weeks. Anticipated full replacement doses may be initiated in individuals who are otherwise young and healthy. In elderly patients or those with known ischemic heart disease, treatment should begin with one fourth to one half the expected dose, and the dose should be adjusted in small increments no sooner than 4-6 weeks.
Achieving a TSH level within the reference range may be slowed because of delay of hypothalamic-pituitary axis readaptation and may take several months. After dose stabilization, patients can be monitored with annual clinical evaluations and TSH monitoring. Patients should be monitored for symptoms and signs of overtreatment, which include tachycardia, palpitations, nervousness, tiredness, headache, increased excitability, sleeplessness, tremors, and possible angina.
A meta-analysis of randomized controlled trials of thyroxine-triiodothyronine combination therapy (T4 + T3) versus thyroxine monotherapy (T4) for treatment of clinical hypothyroidism found no difference in the effectiveness of the combination vs monotherapy in bodily pain, depression, fatigue, body weight, anxiety, quality of life, total cholesterol, LDL-C, HDL-C and triglyceride levels. Hence, T4 monotherapy remains the treatment of choice.12
Pregnancy
Hypothyroidism in pregnancy is associated with preeclampsia, anemia, postpartum hemorrhage, cardiac ventricular dysfunction, spontaneous abortion, low birth weight, impaired cognitive development, and fetal mortality. Even mild disease may be associated with adverse affects for offspring.
Increased dosage requirements should be anticipated during pregnancy, especially in the first and second trimesters. Studies have suggested that patients with hypothyroidism should augment the LT4 dose by 30% at the confirmation of pregnancy, followed by adjustments according to TSH levels. For previously diagnosed women, serum TSH should be measured every 3-4 weeks during the first half of pregnancy and every 6 weeks thereafter. LT4 dose should be adjusted to maintain a serum TSH less than 2.5 mIU/L. TSH and free T4 levels should be measured every 3-4 weeks after every dosage adjustment.13
Autoimmune thyroid disease without overt hypothyroidism has been associated with a higher miscarriage rate. Negro et al showed that euthyroid Caucasian women with positive anti-TPO antibodies treated with levothyroxine during the first trimester had lower miscarriage rates when compared with those who were not treated. They also had lower incidence of premature delivery, comparable to women without thyroid antibodies.14 This will need to be confirmed by other studies, and, if confirmed, there will be an indication to treat euthyroid pregnant women who have thyroid antibodies.
LT4 should not be taken with prenatal vitamin preparations containing iron and calcium. After delivery, the LT4 dose can be reduced to the prepregnancy level and TSH should be checked in 6 weeks.
Subclinical hypothyroidism
Significant controversy persists regarding the treatment of patients with mild hypothyroidism. Some have argued that treatment of these patients improves symptoms, prevents progression to overt hypothyroidism, and may have cardioprotective benefits. Reviews by the US Preventive Services Task Force15 and an independent expert panel16 found inconclusive evidence to recommend aggressive treatment of patients with TSH levels of 4.5-10 mIU/L. The Endocrine Society recommends thyroxine replacement in pregnant women with subclinical hypothyroidism17 ; the American College of Obstetricians and Gynecologists does not recommend it as a routine measure.18
Ultrasonography may have prognostic value in subclinical hypothyroidism. In an Italian study, progression to overt hypothyroidism occurred more often in patients whose ultrasonographic thyroid scan showed diffuse hypoechogenicity (an indication of chronic thyroiditis).19
Following subclinical hypothyroidism and treating on a case-by-case basis is reasonable. Treatment of subclinical hypothyroidism has been shown to reduce total cholesterol, non-HDL cholesterol, and apolipoprotein B,20 and to decrease arterial stiffness and systolic blood pressure.21 In patients with concomitant subclinical hypothyroidism and iron deficiency anemia, iron supplementation may be ineffective if LT4 is not given.22
The American Association of Clinical Endocrinologists (AACE) guidelines state that treatment is indicated in patients with TSH levels above 10 mIU/mL or in patients with TSH levels between 5 and 10 mIU/mL in conjunction with goiter and/or positive antithyroid peroxidase antibodies, as these patients have the highest rates of progression to overt hypothyroidism. An initial dose of 25-50 mcg/d of LT4 can be used and can be titrated every 6-8 weeks, to achieve a target TSH of between 0.3 and 3 mIU/mL.23
Myxedema coma
An effective approach is to use intravenous LT4 at a dose of 4 mcg/kg of lean body weight, or approximately 200-250 mcg as a bolus in a single or divided dose, depending on the patient's risk of cardiac disease followed by 100 mcg 24 hours later and then 50 mcg daily IV or PO along with stress doses of intravenous glucocorticoids. Adjustment of the dose can then be made based on clinical and laboratory along with stress doses of intravenous glucocorticoids. Use of intravenous triiodothyronine is controversial and based on expert opinion. It has a higher frequency of adverse cardiac events and is generally reserved for patients who are not improving clinically on LT4. LT3 can be given initially as a 10 mcg IV bolus and repeated every 8-12 hours until the patient can take maintenance oral doses of T4. Advanced age, high dose T4 therapy, and cardiac complications had the highest associations with mortality.24
Surgical Care
Surgery is indicated for large goiters that compromise tracheoesophageal function; surgery is rarely needed in patients with hypothyroidism and is more common in the treatment of hyperthyroidism.
Consultations
Patients with a nodular thyroid, suspicious thyroid nodules, or compressive symptoms such as dysphagia; pregnant women; patients with underlying cardiac disorders or other endocrine disorders; persons younger than 18 years; and those unresponsive to treatment should be referred to an endocrinologist.
Some patients with thyroiditis can develop hyperthyroidism (or symptoms consistent with hyperthyroidism) before developing hypothyroidism and may benefit from consultation with an endocrinologist.
Suspected myxedema coma is a medical emergency with a high risk of mortality that requires initiation of parenteral (intravenous) LT4 and glucocorticoids prior to laboratory confirmation. An urgent endocrinology consultation should be obtained.
Rarely an increase in size of a goiter in a patient with autoimmune thyroid disease could be a lymphoma and should be evaluated by an endocrinologist.
Diet
No specific diets are required for hypothyroidism.
Subclinical hypothyroidism has been seen in increased frequency in patients with greater iodine intake. The World Health Organization recommends a daily dietary iodine intake of 150 mcg for adults, 200 mcg for pregnant and lactating women, and 50-120 mcg for children.
Activity
Patients who have hypothyroidism have generalized hypotonia and may be at risk for ligamental injury, particularly from excessive force across joints. Thus, patients should exercise caution with certain activities, such as contact sports or heavy physical labor.
Patients with uncontrolled hypothyroidism may have difficulty maintaining concentration in low-stimulus activities and may have slowed reaction times. Patients should use caution if an activity has a risk of injury (eg, operating presses or heavy equipment, driving).
Medication
The goals of pharmacotherapy are to reduce morbidity and to prevent complications.
Thyroid hormone replacement
Levothyroxine is generally considered to be the treatment of choice for patients with hypothyroidism.
Levothyroxine (Synthroid, Levoxyl, Levothroid, Unithroid)
In active form, influences growth and maturation of tissues. Involved in normal growth, metabolism, and development. Produces stable levels of T3 and T4. Administered as a single dose in the morning on an empty stomach. May be administered PO/IV/IM. Has long half-life (7-10 d), and parenteral dosing is rarely needed (except when PO is unavailable, patient is on continuous enteral feeds, or in emergency, such as myxedema coma). Initial subtherapeutic doses are recommended to avoid the stress of rapid metabolic change in elderly patients and in those with coronary artery disease or severe COPD.
* Dosing
* Interactions
* Contraindications
* Precautions
Adult
1.6 mcg/kg/d PO; higher doses may be required in pregnancy; in elderly and those with coronary disease or severe COPD, start at 25-50 mcg/d PO, increase by 25-50 mcg/d q4-8wk until desired response achieved
Maintenance: 50-200 mcg PO qam
Subclinical hypothyroidism: If treated an initial dose of LT4 25-50 mcg/d can be used and titrated q6-8wk to achieve a target TSH between 0.3 and 3 mIU/mL
Myxedema coma: 200-250 mcg IV bolus, followed by 100 mcg the next day and then 50 mcg/d PO or IV along with T3; use smaller doses in patients with cardiovascular disease; patients should first receive stress dose steroids in case they have concomitant primary or secondary adrenal insufficiency (see above)
Pediatric
Neonate to 6 months: 25-50 mcg/d PO
6-12 months: 50-75 mcg/d PO
1-6 years: 75-100 mcg/d PO
6-12 years: 100-150 mcg/d PO
>12 years: 150 mcg/d PO
* Dosing
* Interactions
* Contraindications
* Precautions
Hepatic enzyme inducers (phenytoin) may increase degradation of, antidiabetic agents, theophylline, adrenocorticoids, digoxin, and anticoagulants, which may need dose adjustments; IV phenytoin may release thyroid hormone from thyroglobulin; effects of TCAs and sympathomimetics may be increased; cholestyramine, sucralfate, iron may decrease absorption; estrogens may decrease response to thyroid hormone therapy in patients with nonfunctioning thyroid glands; activity of some beta-blockers may decrease when patient with hypothyroidism is converted to a euthyroid state; beta-blockers may decrease conversion of T3 to T4
* Dosing
* Interactions
* Contraindications
* Precautions
Documented hypersensitivity, uncorrected adrenal insufficiency; acute MI uncomplicated by hypothyroidism; untreated thyrotoxicosis
* Dosing
* Interactions
* Contraindications
* Precautions
Pregnancy
A - Fetal risk not revealed in controlled studies in humans
Precautions
Caution in elderly patients and patients with renal insufficiency, hypertension, ischemia, angina, and other cardiovascular diseases; periodically monitor thyroid status; because of the risk of adrenal crisis, T4 should not be administered without corticosteroids in any patient with suspected adrenal insufficiency, either primary or secondary
Liothyronine (Cytomel, Triostat)
Synthetic form of the natural thyroid hormone T3 converted from T4. Used when a rapid effect is desired perioperatively or for nuclear medicine studies. Not intended as sole maintenance therapy. Can be used in combination with levothyroxine in small doses (5-15 mcg/d). Duration of activity is short (half-life is 12-24 h) and allows for quick dosage adjustments in event of overdosage. May be preferred when GI absorption is impaired (95% absorbed compared to 50-80% of T4) or if peripheral conversion is impaired.
Dosage recommendations are for short-term use in special circumstances (see above) with the guidance of an endocrinologist.
* Dosing
* Interactions
* Contraindications
* Precautions
Adult
Initial: 25 mcg/d PO in divided bid; increase by 12.5-25 mcg/d PO q1-2wk until desired response achieved
Maintenance: 50-100 mcg/d PO
Myxedema coma: 10 mcg IV and repeated q8 -12h until patient can take PO maintenance oral dose of T4 (see above)
Elderly patients or patients with suspected or known coronary disease: Avoid because of high risk of cardiovascular manifestations
Pediatric
5 mcg/d PO; increase by 5 mcg q3d until desired response achieved
* Dosing
* Interactions
* Contraindications
* Precautions
Hepatic enzyme inducers (phenytoin) may increase degradation; of antidiabetic agents, theophylline, adrenocorticoids, digoxin, and anticoagulants, these may need dose adjustments; IV phenytoin may release thyroid hormone from thyroglobulin; effects of TCAs and sympathomimetics may be increased; cholestyramine may decrease absorption; estrogens may decrease response to thyroid hormone therapy in patients with nonfunctioning thyroid glands; activity of some beta-blockers may decrease when hypothyroid patient converted to euthyroid state; beta-blockers may decrease conversion of T3 to T4
* Dosing
* Interactions
* Contraindications
* Precautions
Documented hypersensitivity; uncorrected adrenal insufficiency; acute MI uncomplicated by hypothyroidism; untreated thyrotoxicosis; cardiac arrhythmias; suspected or known coronary disease
* Dosing
* Interactions
* Contraindications
* Precautions
Pregnancy
A - Fetal risk not revealed in controlled studies in humans
Precautions
Caution in elderly patients and patients with renal insufficiency, hypertension, ischemia, angina, and other cardiovascular diseases; periodically monitor thyroid status; because of risk of adrenal crisis, liothyronine should not be administered without corticosteroids in any patient with suspected adrenal insufficiency, either primary or secondary
Desiccated thyroid (Armour Thyroid)
Derived from extract of bovine or porcine thyroid glands. Some manufacturers standardize based on bioassays; others use iodine content. Desiccated thyroid is referred to as natural thyroid and generally contains T3 and T4 in a 1:4 ratio. It is made in the following strengths 1/8, 1/4, 1/2, 1, 2, and 3 grain as well as 4 and 5 grain tabs. One grain (60 mg) contains about 38 mcg of T4 and 9 mcg of T3. Because these preparations contain variable quantities of T3, they should not be prescribed for patients with known or suspected cardiac disease (see above).
* Dosing
* Interactions
* Contraindications
* Precautions
Adult
Initial: 30 mg/d PO; increase by 15-30 mg/d PO q4wk until desired response achieved
Maintenance: 60-180 mg/d PO
Pediatric
Neonate to 6 months: 15-30 mg/d PO
6-12 months: 30-45 mg/d PO
1-6 years: 45-60 mg/d PO
6-12 years: 60-90 mg/d POFollow-up
Further Inpatient Care
* Most patients can be treated in an ambulatory care setting.
* Patients with severe hypothyroidism, myxedema, require aggressive management in an inpatient setting.
* Overreplacement with LT4 may precipitate tachyarrhythmias or, rarely, thyroid storm, which may require hospitalization. Risk is higher with T3.
* Patients who require long-term continuous tube feeding require IV LT4 replacement, as the absorption of oral agents is impaired by contents of tube feeds.
Further Outpatient Care
* Once appropriate therapeutic dose is obtained, patients can be monitored annually or semiannually with laboratory evaluation and physical examination.
* Patients should take thyroid hormone as a single dose in the morning to avoid insomnia. Thyroid hormone is better absorbed in the small bowel; therefore, absorption can be affected by malabsorptive states, small bowel disease, and the patient's age. Many drugs (eg, iron, calcium carbonate, aluminum hydroxide, sucralfate [Carafate]) can interfere with absorption. Emphasize proper compliance at each visit.
* In addition, monitor patients for signs of excess dosing (eg, nervousness, palpitations, diarrhea, excessive sweating, heat intolerance, chest pain). Monitor pulse rate, blood pressure, and vital signs. In children, sleeping pulse rate and basal temperature can be used as guides to adequate clinical response to treatment.
Deterrence/Prevention
No universal screening recommendations exist for thyroid disease for adults. All neonates should be screened for thyroid disease.
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 (eg, pregnant women, women >60 y, patients with type 1 diabetes or other autoimmune disease, patients with history of neck irradiation).25
The American College of Physicians recommends screening all women older than 50 years who have one or more clinical features of disease.26,27
The American Association of Clinical Endocrinologists recommends TSH measurements of all women of childbearing age before pregnancy or during the first trimester.23
TheUS Preventive Task Force concludes that the evidence is insufficient to recommend for or against routine screening for thyroid disease in adults (grade I recommendation).15
Because screening prevents a delay in recognition and treatment of cretinism, governmental bodies frequently mandate screening of neonates.
Complications
* Thyroid hormone replacement can precipitate adrenal crises in patients with untreated adrenal insufficiency. If suspected, the presence of adrenal insufficiency should be confirmed or ruled out and should be treated prior to treatment of hypothyroidism.
* Aggressive replacement of thyroid hormone may compromise cardiac function in patients with existing cardiac disease. In these patients, administer smaller initial doses of LT4 with small incremental increases.
* Subclinical hyperthyroidism, which can result from treatment with L-thyroxine, is more common, but its relationship to osteoporosis and fracture is unclear. Previously, osteoporosis was thought to be a risk of TSH suppression below the normal range; however, later studies did not consistently confirm this hypothesis except in postmenopausal women.28 Nonetheless, patients at risk for osteoporosis (eg, women who are estrogen deficient) and individuals receiving a long-term suppressive of LT4 (eg, patients with differentiated thyroid cancer) should be closely monitored. Note that patients with thyroid cancer are usually on a higher dose of LT4. Desired TSH depends on the staging of their thyroid cancer. In patients with stage IV thyroid cancer, it is desirable to keep their TSH below 0.1 mIU/L.
* Advise patients that vision may temporarily worsen when starting hormone therapy. Rarely, pseudotumor cerebri occurs.
* Patients with depression may develop mania, and psychosis may be exacerbated in patients with severe psychological illness.
* Because most brain growth occurs in the first 2 years of life, untreated hypothyroidism in infants can cause irreversible mental retardation. Older infants are spared nervous system damage but continue to have slowed physical and linear bone growth. They also have delayed dental development.
Prognosis
* Undertreatment leads to disease progression with gradual worsening of symptoms and further metabolic derangements.
* Fortunately, in most patients older than 3 years, the signs and symptoms of hypothyroidism are reversed with thyroid hormone treatment.
* With treatment, circulating lipid levels should improve to a mild degree. This may result in a decrease of coronary artery disease (CAD).
Patient Education
* Clearly discuss the life-long nature of hypothyroidism, the need for life-long therapy, the proper way to take medicine, and the minimum need for annual TSH testing.
* For excellent patient education resources, visit eMedicine's Endocrine System Center and Muscle Disorders Center. Also, see eMedicine's patient education articles Thyroid Problems and Chronic Fatigue Syndrome.
Miscellaneous
Medicolegal Pitfalls
* Aggressive treatment in the presence or suggestion of cardiac disease may raise the risk of mortality.
* A delay in the diagnosis and treatment of hypothyroidism in an infant with cretinism may lead to irreversible CNS damage. Legally mandated screening of neonates confers additional legal requirements on institutions, laboratories, and other nonphysician entities for compliance with, quality of, and follow-up for abnormal screening.
