Hypothyroidism

Q-Notes for Adult Medicine TOC | ENDO

HYPOTHYROIDISM

HYPOTHYROIDISM

DX   | SX | LAB | Diff-Dx | RX REF: ACP PIER 2006

Diagnosis of Hypothyroidism - elevated TSH with low or normal FT4
Serum TSH is the test of choice to detect the presence of primary hypothyroidism.

In the earliest stage of primary hypothyroidism, an increased serum TSH often is the only detectable laboratory abnormality.
Patients with elevated serum TSH levels progress to more severe degrees of thyroid failure at a rate of 5% to 18% per year.
Serum TSH levels may be transiently elevated in euthyroid persons recovering from a non-thyroidal illness.
Serum TSH levels may be transiently decreased by the administration of medications such as glucocorticoids, dopamine, and octreotide.

Diagnosis

Use a complete history, physical exam, and basic lab evaluation to allow for accurate assessment.
Measure serum TSH and T4 to evaluate the site of the disorder causing hypothyroidism and to evaluate severity of hypothyroidism.
Measure serum antithyroid antibodies to help determine the cause of primary hypothyroidism and predict the progression of subclinical to overt hypothyroidism.

Thyroid Blood tests

Thyroid-stimulating hormone (TSH): In most cases, this is the single most useful lab test in diagnosing thyroid disease. When there is an excess of thyroid hormone in the blood, as in hyperthyroidism, the TSH is low. When there is too little thyroid hormone, as in hypothyroidism, the TSH is high.
Free (T4): T4 is one of the thyroid hormones. High T4 may indicate hyperthyroidism. Low T4 may indicate hypothyroidism.
Triiodothyronine (T3): T3 is another one of the thyroid hormones. High T3 may indicate hyperthyroidism. Low T3 may indicate hypothyroidism.
TSH receptor antibody (TSI): This antibody is present in Grave's disease.
Antithyroid antibody: This antibody is present in Hashimoto and Grave's disease.

Thyroid scan:

For this test, a small amount of radioactive iodine is injected into the blood, and then an x-ray image of the thyroid is taken. Increased uptake of the radioactive material in the thyroid gland indicates hyperthyroidism, while decreased uptake is present in hypothyroidism. This test should not be done on pregnant women.

Thyroid ultrasound:

This exam helps to differentiate between different types of nodules of the thyroid gland.

Thyroid Fine-needle aspiration:

For this test, a small needle is inserted into the thyroid gland in order to get a sample of thyroid tissue, usually from a nodule. The tissue is then observed under a microscope by a pathologist to look for any signs of cancer.

DX   | SX | LAB | Diff-Dx | RX

History & Physical Examination Elements of Hypothyroidism
HISTORY

Weakness 99% of cases, Lethargy 91% of cases, Fatigue 84%-90%, Cold intolerance 59%-89%, Impaired memory 66%, Diminished sweating 34%-89%, Weight gain 49-63%, Menstrual problems 58%, Paresthesias 52%, Constipation 40%-61%, Anorexia 19%-45%, Hair loss 44%-45%, Sleepiness 40%, Impaired learning 22% of cases .

PHYSICAL EXAM

Dry skin 62%-97% of cases, Coarse skin 60%-97%, Periorbital puffiness 60%-90%, Bradycardia 50%-60%, Cold skin 50%, Coarse hair 40%-66%, Slow movements 36%-70%, Slow speech 48%-65%, Hoarseness 34%-66%, Hypertension, diastolic 20%-40%, Goiter 15%-40% of cases.

DX   | SX | LAB | Diff-Dx | RX

Laboratory and Other Studies for Hypothyroidism

TSH, Free T4, Total T4, T3, ESR
Serum Anti-TPO antibodies (anti-thyroid peroxidase) or anti-thyroglobulin antibodies

Hormone Changes Occurring During the Development of Primary Hypothyrodism

In mild thyroid failure, the only detectable abnormality is a mildly elevated serum TSH level, and normal serum T4.
In moderate hypothyroidism, there is further elevation of serum TSH and a reduction in serum T4, but the T3 level is relatively preserved by enhanced T4 to T3 conversion.
In severe hypothyroidism, the TSH level is very high, the T4 level is further reduced, and the serum T3 level becomes low.

Hormone Changes Occurring During the Development of Central Hypothyroidism

Because this disorder is due to impaired pituitary TSH secretion, the serum TSH level does not rise and thus there is no signal of mild thyroid failure.
When central hypothyroidism is moderate, the serum T4 level becomes low, the serum T3 level remains normal and the serum TSH is low or low-normal.
Severe central hypothyroidism is characterized by very low serum T4 level, low serum T3 level, and a low or low-normal serum TSH level.

DX   | SX | LAB | Diff-Dx | RX

Differential Diagnosis of Hypothyroidism

Hashimoto's thyroiditis : TSH high; TPO antibodies. Slowly progressive

Thyroidectomy: TSH high; history of surgery. Surgical scar

Radioiodine therapy: TSH high; history of 131-I treatment. History of thyrotoxicosis

External radiation therapy: TSH high; history of radiation therapy. History of cancer

Iodine deficiency: TSH high; urine iodine low. Iodine deficient area

Painless postpartum thyroiditis : TSH high; TPO antibodies. Recent pregnancy

Silent thyroiditis: TSH high; TPO antibodies. Recent thyrotoxicosis

Painful Subacute thyroiditis TSH high; painful; ESR elevated. Recent thyrotoxicosis

Drug induced TSH high; use of amiodarone, lithium, interferon, iodine, or thionamides. Medication history

Pituitary/hypothalamic mass: TSH low or normal; FT4 low; Abnormal MRI/CT scan. Headaches, visual field cuts, ophthalmoplegia

Pituitary/hypothalamic surgery: TSH low or normal; FT4 low. History of surgery

Pituitary/hypothalamicRadiation therapy: TSH low or normal; free T4 low. History of radiation therapy

Pituitary/hypothalamic infiltration/infection: TSH low or normal; free T4 low; Abnormal MRI/CT scan. Headaches, visual field cuts, ophthalmoplegia

DX   | SX | LAB | Diff-Dx | RX

Drug Therapy of Hypothyroidism

In most cases, use LT4 (the agent of choice) rather than LT3, a combination of the two, or dessicated thyroid in treating patients with hypothyroidism.

Note that name-brand LT4 products are preferred over generic preparations.
Generic and brand-name LT4 preparations differ significantly in potency from brand to brand.
Most experts currently recommend using brand-name LT4 products and advise against switching between preparations. .

Treat overt hypothyroidism with LT4 based on the patient's age, body weight, and underlying health..

Treat overt hypothyroidism in a patient over 60 with an initial LT4 dose of 25 to 50 µg/d and increase in 25 µg increments every 6 to 8 weeks until the desired dose is reached..

Treat overt hypothyroidism in a patient with known or suspected heart disease with an initial LT4 dose of 12.5 to 25 µg/d and increase in 12.5 to 25 µg increments every 6 weeks until the desired dose is reached..

Treat myxedema coma with LT4, LT3, or a combination of the two; add hydrocortisone, 100 mg iv every 8 hours for 2 days; and target appropriate therapy to possible precipitating illness, such as sepsis..

Treat subclinical hypothyroidism (mild thyroid failure) with LT4 under certain circumstances..

Treat most subclinical hypothyroidism patients who have a serum TSH level of >10 mU/L, particularly if they have symptoms of thyroid hormone deficiency, when their serum LDL cholesterol is elevated, or when they have positive serum antithyroid antibodies..

Consider treating patients who have a serum TSH level of 5 to 10 mU/L if they have symptoms suggestive of thyroid hormone deficiency, an elevated serum LDL cholesterol level, a goiter, or high levels of antithyroid antibodies..

Treat subclinical hypothyroidism with either an initial full replacement dose of 1.6 µg/kg·d or with a lower dose of 25 to 50 µg/d and increase the dose in 25 µg increments until the desired dose is reached.

Drug Treatment for Hypothyroidism

Synthroid or Levoxyl (levothyroxine (LT4)) PO 1.6 µg/kg/d Effective, reliable, inexpensive. Consistent potency, first-line agent

Thyrolar (liotrix) (T4/T3 combination) 50 µg/12.5 µg – 100 µg/25 µg. T3/T4 ratio too high, not recommended at present

Desiccated thyroid Hormone replacement (T4/T3 combination) 1-2 grains/d. T3/T4 ratio too high, not recommended at present

Cytomel (triiodothyronine (LT3)) 5-12.5 µg/d, Pure T3; short acting, Thyrotoxic T3 level 2-6 hours after dose taken, not recommended at present for most patients.

Synthroid (parenteral levothyroxine (LT4)) 500 µg, then 50-100 µg/d for myxedema coma. 80% of usual oral dose for npo patients.
Benefit: Rapid T4 repletion in myxedema coma. Ensures LT4 delivery for npo patients.
Note: Careful monitoring required. Treatment of myxedema coma. Treatment of hypothyroid patients unable to take oral medications.

Triostat (parenteral triiodothyronine (LT3)) 50-100 µg, then 10-20 µg q 8-12 h, Rapid T3 repletion.
Note: Careful monitoring required. Treatment of myxedema coma.

Hydrocortisone (Adrenal hormone replacement) 100 mg iv q 8 h for 2 days. To cover possible decreased adrenal reserve in myxedema coma
Note: Reviews stress that treatment should be accompanied by administration of intravenous glucocorticoids, support of vital functions, and treatment of any known precipitating events.

Advise patients to take their medication at the same time each day; to avoid taking it within 4 hours of iron tablets, calcium supplements, antacids, and fiber supplements; and that their dosage requirements might change if they take other medications.

Hospitalize patients for intensive monitoring and treatment when myxedema coma is suspected.

Myxedema coma is usually found in elderly patients who have untreated or inadequately treated hypothyroidism and then develop a precipitating event.
Patients should be admitted to an intensive care unit for careful monitoring and appropriate treatment.

Precipitating Factors of Myxedema Coma (Particularly in elderly persons)

Prolonged cold exposure, Sedative use, Infection, Pulmonary embolus, Respiratory failure, Myocardial infarction, Congestive heart failure, Stroke, Gastrointestinal bleeding, Trauma, Surgery

Physical Signs of Myxedema Coma:

Hypothermia, Bradycardia, Hypotension, Hypoventilation, Seizures, Stupor, Coma, Myxedematous skin changes, Periorbital edema, Delayed relaxation of reflexes, Distended abdomen, Ileus, Distended bladder Urinary retention

LAB & Radiology in Myxedema Coma:

Pleural effusions, Radiology Pericardial effusions, Electrocardiogram Low voltage, bradycardia, Macrocytic anemia, Hyponatremia, Elevated creatine kinase, Hypercarbia (CO2 retention), Elevated TSH - need not be significantly elevated, Low serum free T4 - need not be significantly depressed .

DX   | SX | LAB | Diff-Dx | RX

HYPOTHYROIDISM
DX \| SX \| LAB \| Diff-Dx \| RX REF: ACP PIER 2006
Diagnosis of Hypothyroidism - elevated TSH with low or normal FT4 Serum TSH is the test of choice to detect the presence of primary hypothyroidism. In the earliest stage of primary hypothyroidism, an increased serum TSH often is the only detectable laboratory abnormality. Patients with elevated serum TSH levels progress to more severe degrees of thyroid failure at a rate of 5% to 18% per year. Serum TSH levels may be transiently elevated in euthyroid persons recovering from a non-thyroidal illness. Serum TSH levels may be transiently decreased by the administration of medications such as glucocorticoids, dopamine, and octreotide. Diagnosis Use a complete history, physical exam, and basic lab evaluation to allow for accurate assessment. Measure serum TSH and T4 to evaluate the site of the disorder causing hypothyroidism and to evaluate severity of hypothyroidism. Measure serum antithyroid antibodies to help determine the cause of primary hypothyroidism and predict the progression of subclinical to overt hypothyroidism. Thyroid Blood tests Thyroid-stimulating hormone (TSH): In most cases, this is the single most useful lab test in diagnosing thyroid disease. When there is an excess of thyroid hormone in the blood, as in hyperthyroidism, the TSH is low. When there is too little thyroid hormone, as in hypothyroidism, the TSH is high. Free (T4): T4 is one of the thyroid hormones. High T4 may indicate hyperthyroidism. Low T4 may indicate hypothyroidism. Triiodothyronine (T3): T3 is another one of the thyroid hormones. High T3 may indicate hyperthyroidism. Low T3 may indicate hypothyroidism. TSH receptor antibody (TSI): This antibody is present in Grave's disease. Antithyroid antibody: This antibody is present in Hashimoto and Grave's disease. Thyroid scan: For this test, a small amount of radioactive iodine is injected into the blood, and then an x-ray image of the thyroid is taken. Increased uptake of the radioactive material in the thyroid gland indicates hyperthyroidism, while decreased uptake is present in hypothyroidism. This test should not be done on pregnant women. Thyroid ultrasound: This exam helps to differentiate between different types of nodules of the thyroid gland. Thyroid Fine-needle aspiration: For this test, a small needle is inserted into the thyroid gland in order to get a sample of thyroid tissue, usually from a nodule. The tissue is then observed under a microscope by a pathologist to look for any signs of cancer.
DX \| SX \| LAB \| Diff-Dx \| RX
History & Physical Examination Elements of Hypothyroidism HISTORY Weakness 99% of cases, Lethargy 91% of cases, Fatigue 84%-90%, Cold intolerance 59%-89%, Impaired memory 66%, Diminished sweating 34%-89%, Weight gain 49-63%, Menstrual problems 58%, Paresthesias 52%, Constipation 40%-61%, Anorexia 19%-45%, Hair loss 44%-45%, Sleepiness 40%, Impaired learning 22% of cases . PHYSICAL EXAM Dry skin 62%-97% of cases, Coarse skin 60%-97%, Periorbital puffiness 60%-90%, Bradycardia 50%-60%, Cold skin 50%, Coarse hair 40%-66%, Slow movements 36%-70%, Slow speech 48%-65%, Hoarseness 34%-66%, Hypertension, diastolic 20%-40%, Goiter 15%-40% of cases.
DX \| SX \| LAB \| Diff-Dx \| RX
Laboratory and Other Studies for Hypothyroidism TSH, Free T4, Total T4, T3, ESR Serum Anti-TPO antibodies (anti-thyroid peroxidase) or anti-thyroglobulin antibodies Hormone Changes Occurring During the Development of Primary Hypothyrodism In mild thyroid failure, the only detectable abnormality is a mildly elevated serum TSH level, and normal serum T4. In moderate hypothyroidism, there is further elevation of serum TSH and a reduction in serum T4, but the T3 level is relatively preserved by enhanced T4 to T3 conversion. In severe hypothyroidism, the TSH level is very high, the T4 level is further reduced, and the serum T3 level becomes low. Hormone Changes Occurring During the Development of Central Hypothyroidism Because this disorder is due to impaired pituitary TSH secretion, the serum TSH level does not rise and thus there is no signal of mild thyroid failure. When central hypothyroidism is moderate, the serum T4 level becomes low, the serum T3 level remains normal and the serum TSH is low or low-normal. Severe central hypothyroidism is characterized by very low serum T4 level, low serum T3 level, and a low or low-normal serum TSH level.
DX \| SX \| LAB \| Diff-Dx \| RX
Differential Diagnosis of Hypothyroidism Hashimoto's thyroiditis : TSH high; TPO antibodies. Slowly progressive Thyroidectomy: TSH high; history of surgery. Surgical scar Radioiodine therapy: TSH high; history of 131-I treatment. History of thyrotoxicosis External radiation therapy: TSH high; history of radiation therapy. History of cancer Iodine deficiency: TSH high; urine iodine low. Iodine deficient area Painless postpartum thyroiditis : TSH high; TPO antibodies. Recent pregnancy Silent thyroiditis: TSH high; TPO antibodies. Recent thyrotoxicosis Painful Subacute thyroiditis TSH high; painful; ESR elevated. Recent thyrotoxicosis Drug induced TSH high; use of amiodarone, lithium, interferon, iodine, or thionamides. Medication history Pituitary/hypothalamic mass: TSH low or normal; FT4 low; Abnormal MRI/CT scan. Headaches, visual field cuts, ophthalmoplegia Pituitary/hypothalamic surgery: TSH low or normal; FT4 low. History of surgery Pituitary/hypothalamicRadiation therapy: TSH low or normal; free T4 low. History of radiation therapy Pituitary/hypothalamic infiltration/infection: TSH low or normal; free T4 low; Abnormal MRI/CT scan. Headaches, visual field cuts, ophthalmoplegia
DX \| SX \| LAB \| Diff-Dx \| RX
Drug Therapy of Hypothyroidism In most cases, use LT4 (the agent of choice) rather than LT3, a combination of the two, or dessicated thyroid in treating patients with hypothyroidism. Note that name-brand LT4 products are preferred over generic preparations. Generic and brand-name LT4 preparations differ significantly in potency from brand to brand. Most experts currently recommend using brand-name LT4 products and advise against switching between preparations. . Treat overt hypothyroidism with LT4 based on the patient's age, body weight, and underlying health.. Treat overt hypothyroidism in a patient over 60 with an initial LT4 dose of 25 to 50 µg/d and increase in 25 µg increments every 6 to 8 weeks until the desired dose is reached.. Treat overt hypothyroidism in a patient with known or suspected heart disease with an initial LT4 dose of 12.5 to 25 µg/d and increase in 12.5 to 25 µg increments every 6 weeks until the desired dose is reached.. Treat myxedema coma with LT4, LT3, or a combination of the two; add hydrocortisone, 100 mg iv every 8 hours for 2 days; and target appropriate therapy to possible precipitating illness, such as sepsis.. Treat subclinical hypothyroidism (mild thyroid failure) with LT4 under certain circumstances.. Treat most subclinical hypothyroidism patients who have a serum TSH level of >10 mU/L, particularly if they have symptoms of thyroid hormone deficiency, when their serum LDL cholesterol is elevated, or when they have positive serum antithyroid antibodies.. Consider treating patients who have a serum TSH level of 5 to 10 mU/L if they have symptoms suggestive of thyroid hormone deficiency, an elevated serum LDL cholesterol level, a goiter, or high levels of antithyroid antibodies.. Treat subclinical hypothyroidism with either an initial full replacement dose of 1.6 µg/kg·d or with a lower dose of 25 to 50 µg/d and increase the dose in 25 µg increments until the desired dose is reached. Drug Treatment for Hypothyroidism Synthroid or Levoxyl (levothyroxine (LT4)) PO 1.6 µg/kg/d Effective, reliable, inexpensive. Consistent potency, first-line agent Thyrolar (liotrix) (T4/T3 combination) 50 µg/12.5 µg – 100 µg/25 µg. T3/T4 ratio too high, not recommended at present Desiccated thyroid Hormone replacement (T4/T3 combination) 1-2 grains/d. T3/T4 ratio too high, not recommended at present Cytomel (triiodothyronine (LT3)) 5-12.5 µg/d, Pure T3; short acting, Thyrotoxic T3 level 2-6 hours after dose taken, not recommended at present for most patients. Synthroid (parenteral levothyroxine (LT4)) 500 µg, then 50-100 µg/d for myxedema coma. 80% of usual oral dose for npo patients. Benefit: Rapid T4 repletion in myxedema coma. Ensures LT4 delivery for npo patients. Note: Careful monitoring required. Treatment of myxedema coma. Treatment of hypothyroid patients unable to take oral medications. Triostat (parenteral triiodothyronine (LT3)) 50-100 µg, then 10-20 µg q 8-12 h, Rapid T3 repletion. Note: Careful monitoring required. Treatment of myxedema coma. Hydrocortisone (Adrenal hormone replacement) 100 mg iv q 8 h for 2 days. To cover possible decreased adrenal reserve in myxedema coma Note: Reviews stress that treatment should be accompanied by administration of intravenous glucocorticoids, support of vital functions, and treatment of any known precipitating events. Advise patients to take their medication at the same time each day; to avoid taking it within 4 hours of iron tablets, calcium supplements, antacids, and fiber supplements; and that their dosage requirements might change if they take other medications. Hospitalize patients for intensive monitoring and treatment when myxedema coma is suspected. Myxedema coma is usually found in elderly patients who have untreated or inadequately treated hypothyroidism and then develop a precipitating event. Patients should be admitted to an intensive care unit for careful monitoring and appropriate treatment. Precipitating Factors of Myxedema Coma (Particularly in elderly persons) Prolonged cold exposure, Sedative use, Infection, Pulmonary embolus, Respiratory failure, Myocardial infarction, Congestive heart failure, Stroke, Gastrointestinal bleeding, Trauma, Surgery Physical Signs of Myxedema Coma: Hypothermia, Bradycardia, Hypotension, Hypoventilation, Seizures, Stupor, Coma, Myxedematous skin changes, Periorbital edema, Delayed relaxation of reflexes, Distended abdomen, Ileus, Distended bladder Urinary retention LAB & Radiology in Myxedema Coma: Pleural effusions, Radiology Pericardial effusions, Electrocardiogram Low voltage, bradycardia, Macrocytic anemia, Hyponatremia, Elevated creatine kinase, Hypercarbia (CO2 retention), Elevated TSH - need not be significantly elevated, Low serum free T4 - need not be significantly depressed .
DX \| SX \| LAB \| Diff-Dx \| RX

2010