PANCE Blueprint Endocrinology (6%)

Hypothyroidism

Patient will present as → a 43-year-old female with complaints of increased fatigue and a 10-lb weight gain over the last 2 months. She states that she "feels cold" all the time, has decreased energy, and is experiencing worsening constipation. She has also been having heavy periods. On physical exam, her pulse is 45/minute, her skin is dry and cold, and her eyebrows are thinned. You notice delayed deep tendon reflexes. Routine blood tests demonstrate a TSH level of 9.5 uU/mL (normal 0.35 to 5.0 uU/ml) and Thyroxine (T4), serum: 9.8 ug/dL (normal 5-12 ug/dL).

Hypothyroidism is a condition in which the thyroid gland doesn't produce enough thyroid hormone.

  • The most common cause Hashimoto's thyroiditis which is an autoimmune-mediated form of hypothyroidism. The body’s immune system attacks the thyroid tissue, preventing the normal secretion of thyroid hormones.
  • Labs: ↑ TSH and ↓ Free T4

Labs: ↑ TSH and ↓ Free T4871px-Thyroid_system.svg

  • Thyroid hormone levels may be normal early in the disease. The TSH level will be elevated, though, and the thyroid hormone levels will begin to decrease as the disease progresses.
  • In primary hypothyroidism, there is no feedback inhibition of the intact pituitary, and serum TSH is always elevated, whereas serum free T4 is low.
    • In secondary hypothyroidism, free T4 and serum TSH are low (sometimes TSH is normal but with decreased bioactivity).
  • Free thyroxine (T4)
    • Many patients with primary hypothyroidism have normal circulating levels of triiodothyronine (T 3 ), probably caused by sustained TSH stimulation of the failing thyroid, resulting in preferential synthesis and secretion of biologically active T 3. Therefore, serum T 3 is not sensitive for hypothyroidism.
"Subclinical hypothyroidism occurs in the early stages of thyroid function inadequacy. The hypothalamic-pituitary axis recognizes falling serum T4 levels and increases TSH function accordingly. TSH, serum: 11.2 uU/mL (normal 0.5-5.0 uU/mL) and Thyroxine (T4), serum: 9.8 ug/dL (normal 5-12 ug/dL). Patients with the disease should be treated with thyroxine in the event of goiter, hypercholesterolemia, symptoms of hypothyroidism, or TSH levels > 20 uU/mL. "

Diagnosis of Hashimoto's is confirmed by antithyroid peroxidase (TPO) antibodies

  • Anemia is often present, usually normocytic-normochromic and of unknown etiology, but it may be hypochromic because of menorrhagia and sometimes macrocytic because of associated pernicious anemia or decreased absorption of folate.
  • Serum cholesterol is usually high in primary hypothyroidism but less so in secondary hypothyroidism.

Thyroid replacement hormone therapy

TSH levels are regularly performed (measured six weeks after initiation and any changes in dosing until normal levels are achieved) to measure the thyroid hormone levels and ensure that patients have reached a therapeutic dose of hormone replacement therapy.

  • Thyroxine, adjusted until TSH levels are in mid normal range
    • Oral T4 ( L -thyroxine) (Levoxyl, Synthroid) is the preferred treatment and is given in the lowest dose that restores serum TSH levels to the mid-normal range
    • Treatment should be continued through pregnancy.

Complications: Hashimoto encephalopathy, goiter, heart failure, depression, decreased libido, myxedema

IM_NUR_HypothyroidIntervention_v1.3_ Hypothyroidism occurs as a result of a decreased level of thyroid hormone, which occurs following thyroidectomy, radioactive iodine (RAI) ablation, and in some geographic areas in the world where the soil is lacking in iodine leading to iodine deficiency and goiter. Overall clinical symptoms of hypothyroidism relate to decreased metabolism.

Hypothyroidism Assessment Picmonic

The goal for treating patients with hypothyroidism is to bring the TSH and T4 back to a normal range and to alleviate symptoms. Patients will be on medication for life. Extensive education needs to be done on medication side effects and possible consequences of not taking the medication.

Hypothyroidism Intervention Picmonic

IM_MED_HashimotoThyroiditis_v1.4_ Hashimoto's thyroiditis is an autoimmune disorder leading to hypothyroidism. Patients typically complain of thyroid goiter and hypothyroid symptoms, though they may have bouts of hyperthyroidism.

Hashimoto's Thyroiditis Picmonic

Question 1
Which of the following is not a common physical sign of hypothyroidism?
A
Ascites
B
Bradycardia
C
Slowed speech and movements
D
Jaundice
Question 1 Explanation: 
Physical signs of hypothyroidism include:
  • Weight gain
  • Slowed speech and movements
  • Dry skin
  • Jaundice
  • Pallor
  • Coarse, brittle, straw-like hair
  • Loss of scalp hair, axillary hair, pubic hair, or a combination
  • Dull facial expression
  • Coarse facial features
  • Periorbital puffiness
  • Macroglossia
  • Goiter (simple or nodular)
  • Hoarseness
  • Decreased systolic blood pressure and increased diastolic blood pressure
  • Bradycardia
  • Pericardial effusion
  • Abdominal distention, ascites (uncommon)
  • Hypothermia (only in severe hypothyroid states)
  • Nonpitting edema (myxedema)
  • Pitting edema of lower extremities
  • Hyporeflexia with delayed relaxation, ataxia, or both
Question 2
Myxedema coma is a severe form of hypothyroidism that most commonly occurs in which of the following?
A
Male patients with hypothyroidism and excessive weight gain
B
Female patients with galactorrhea and menstrual disturbances secondary to hypothyroidism
C
Patients with hypothyroidism and decreased appetite, sleepiness, hair loss, and dry skin
D
Patients with untreated hypothyroidism who are subjected to an external stress
Question 2 Explanation: 
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, myocardial infarction, stroke, or medical intervention (eg, surgery or hypnotic drugs).
Question 3
Which of the following is generally accepted as the most sensitive screening tool for primary hypothyroidism?
A
Free thyroxine (T4) assay
B
Third-generation thyroid-stimulating hormone (TSH) assay
C
Anti-thyroid peroxidase (anti-TPO) antibody assay
D
Antithyroglobulin (anti-Tg) antibody assay
Question 3 Explanation: 
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.
Question 4
In which of the following groups is screening for hypothyroidism recommended?
A
All adults older than 50 years on a routine basis
B
Pregnant women, but not until the second trimester
C
Asymptomatic adults older than 40 years
D
Women older than 50 years who have one or more clinical features of the disease
Question 4 Explanation: 
Screening recommendations from other groups are as follows:
Question 5
Which of the following is the initial treatment indicated in most cases of mild to moderate hypothyroidism?
A
Levothyroxine at a dose of 50-75 µg/day
B
Levothyroxine at a dose of 4 µg per kilogram of lean body weight as an intravenous bolus, with 100 µg administered 24 hours later
C
Desiccated thyroid at a dose of 15-30 mg orally per day
D
Liothyronine at a dose of 25 µg orally per day
Question 5 Explanation: 
The treatment goals for hypothyroidism are to reverse clinical progression and correct metabolic derangements, as evidenced by normal blood levels of TSH and 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. Thyroid hormone can be started at anticipated full replacement doses in individuals who are young and otherwise healthy. In elderly patients and 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 after no less than 4-6 weeks. For most cases of mild to moderate hypothyroidism, a starting levothyroxine dosage of 50-75 µg/day will suffice.
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