Chapter 10

Endocrinology

1 What are the common symptoms and signs of hyperthyroidism?

Symptoms: Nervousness, anxiety, irritability, insomnia, heat intolerance, sweating, palpitations, tremors, weight loss with increased appetite, fatigue, weakness, emotional lability, and diarrhea.

Signs: Enlarged thyroid gland, warm skin, thyroid “stare”—lid lag, exophthalmos, proptosis, ophthalmoplegia (Graves disease), pretibial myxedema (Graves disease), tremor, tachycardia, and atrial fibrillation. Check thyroid-stimulating hormone (TSH) when patients come to the hospital with new-onset atrial fibrillation.

2 What are the most common causes of hyperthyroidism?

The most common cause is Graves disease, which is characterized by a diffusely enlarged thyroid gland, positive thyroid-stimulating immunoglobulins and antibodies, exophthalmos, proptosis, ophthalmoplegia, and pretibial myxedema. In older patients, look for toxic multinodular goiter (individual lumps instead of diffuse enlargement of the gland and “hot” nodules on thyroid nuclear scan). Other causes include adenoma (single lump that is “hot” on nuclear scan), subacute thyroiditis (viral infection with tender, painful thyroid gland), and factitious hyperthyroidism (in which the patient takes thyroid hormone). Rare, exotic causes include amiodarone (which can cause hypothyroidism or hyperthyroidism), TSH-producing pituitary tumor, thyroid carcinoma, and struma ovarii (an ovarian teratoma that secretes thyroid hormone).

3 Describe the classic laboratory pattern of hyperthyroidism

The TSH level is low (unless the patient has a TSH-secreting tumor), whereas triiodothyronine (T₃) and thyroxine (T₄) are increased.

4 How is hyperthyroidism treated?

Short-term (stabilizing) treatment: Propylthiouracil (PTU) and methimazole/carbimazole can be used as suppressive agents. Beta blockers are used in the setting of thyroid storm (severe hyperthyroid state—an emergency). Iodine can also suppress the thyroid gland but is rarely used for this purpose clinically.

Definitive (curative) treatment: Radioactive iodine ablation of the thyroid gland is typically used. Surgery is preferred in pregnant patients. Hypothyroidism may result from either treatment; if so, it is treated with thyroid hormone replacement (for life).

5 What are the symptoms and signs of hypothyroidism?

Symptoms: Weakness, lethargy, fatigue, cold intolerance, weight gain with anorexia, constipation, loss of hair, hoarseness, menstrual irregularity (menorrhagia is classic), myalgias and arthralgias, memory impairment, and dementia. Always rule out hypothyroidism as a cause of dementia.

Signs: Bradycardia; dry, coarse, cold, and pale skin; periorbital and peripheral edema; coarse, thin hair; thick tongue; slow speech; decreased reflexes; hypertension; carpal tunnel syndrome and paresthesias; vitiligo, pernicious anemia, and diabetes (remember the autoimmune association between these three conditions and Hashimoto disease); and coma (severe disease).

In children, congenital hypothyroidism may occur (mental, motor, and growth retardation).

6 What are the common causes of hypothyroidism?

The most common known cause is Hashimoto thyroiditis. Women of reproductive age are affected 8 times more often than men. Histology reveals lymphocytes in the thyroid gland as well as antithyroid and antimicrosomal antibodies. Other autoimmune diseases may coexist. The associated goiter is nontender. The second most common cause is iatrogenic after treatment of hyperthyroidism. Other less common causes include iodine deficiency, amiodarone, lithium, and secondary hypothyroidism because of pituitary or hypothalamic failure (look for decreased TSH), such as with Sheehan syndrome (hypopituitarism caused by pituitary necrosis from blood loss and hypovolemic shock during and after childbirth).

7 Describe the laboratory findings in hypothyroidism

Elevated TSH (unless caused by secondary causes), decreased T₃ and T₄, antithyroid and antimicrosomal antibodies (if caused by Hashimoto thyroiditis), hypercholesterolemia, and anemia (which may be because of chronic disease or coexisting pernicious anemia).

8 Why is free T₄ (or free T₄ index) better than total T₄ for measuring thyroid hormone activity?

Free T₄ (free T₄ index) measures the active form of thyroid hormone. Many conditions cause a change in the amount of thyroid-binding globulin (TBG), thus changing total T₄ levels in the absence of hypothyroidism or hyperthyroidism. Common examples include pregnancy, estrogen therapy, and oral contraceptive pills, all of which increase TBG. Nephrotic syndrome, cirrhosis, and corticosteroid treatment all decrease TBG. T₃ resin uptake is an older test that is not likely to appear on Step 2, but if you are asked, it should rise or fall in the same way as free T₄. Although an oversimplification, this principle should serve you well on the examination.

9 How is hypothyroidism treated?

With T₄ or thyroxine. T₃ should not be used. In older patients, it is important to “start low and go slow” because overtreatment can be dangerous.

10 What is sick euthyroid syndrome?

Any patient with any illness may have temporary derangements in thyroid function tests that resemble hypothyroidism. TSH ranges from normal to mildly elevated, and serum T₄ ranges from normal to mildly decreased. Clinical circumstances and physical findings are the best guides to whether the patient has true hypothyroidism. In patients with sick euthyroid syndrome, simply treat the underlying illness. If the diagnosis is in doubt, repeat the thyroid tests after the patient recovers (preferred) or give an empirical dose of levothyroxine (if the patient does not respond to treatment of the underlying illness).

11 What are the symptoms and signs of Cushing syndrome (increased corticosteroids)?

Symptoms: Weight gain, changes in appearance, easy bruising, acne, hirsutism, emotional lability, depression, psychosis, weakness, menstrual changes, sexual dysfunction, insomnia, and memory loss.

Signs: Buffalo hump, truncal and central obesity with wasting of extremities, round plethoric facies, purplish skin striae, acne, hirsutism, weakness (especially of the proximal muscles), hypertension, depression, psychosis, peripheral edema, poor wound healing, glucose intolerance or diabetes, osteoporosis, and hypokalemic metabolic alkalosis (because of mineralocorticoid effects of certain corticosteroids). Growth may be stunted in children.

12 What causes Cushing syndrome?

The most common cause is iatrogenic because steroids are prescribed for many different disorders. The second most common cause is Cushing disease (a pituitary adenoma that secretes adrenocorticotropic hormone [ACTH]), which causes roughly 60% of noniatrogenic cases. Women of reproductive age are affected 5 times more often than men. Other causes include ectopic ACTH production (classically by small cell lung cancer, which is more common in men) and adrenal adenomas or carcinomas (more common in children).

13 How is Cushing syndrome diagnosed?

The first test is either a 24-hour measurement of free cortisol in urine (free cortisol levels are abnormally elevated) or a dexamethasone suppression test (cortisol levels are not appropriately suppressed several hours after administration of dexamethasone). Random cortisol level is an inappropriate test because of wide interpatient and intrapatient variations. ACTH is elevated in Cushing disease but decreased with an adrenal adenoma. If ACTH is increased, a magnetic resonance imaging (MRI) scan of the brain should be obtained to look for a pituitary adenoma. If ACTH is decreased and the patient has no history of taking steroids, an abdominal computed tomography (CT) or MRI scan should be obtained to look for an adrenal tumor. Primary cancer is usually obvious when ectopic ACTH is the cause (e.g., weight loss, hemoptysis with lung mass on chest radiograph in patients with small cell lung cancer). Treatment is based on the cause and usually involves surgery.

14 What are the symptoms and signs of hypoadrenalism (Addison disease)?

Symptoms: Anorexia, weight loss, weakness, apathy.

Signs: Hypotension, hyperkalemia, hyponatremia, hyperpigmentation (only if the pituitary is functioning because of melanocyte stimulating hormone), nausea and vomiting, diarrhea, abdominal pain, mild fever, hypoglycemia, acidosis, eosinophilia, and shock.

15 What is the most common type of hypoadrenalism?

Secondary (iatrogenic) hypoadrenalism because of steroid treatment. People who are removed from long-term steroid therapy may be unable to secrete an appropriate amount of corticosteroids in response to stress for up to 1 year. Watch for the classic postoperative patient who crashes (with hypotension, shock, and hyperkalemia) shortly after surgery and has a history of a disease requiring steroid therapy within the past year. You may assess ACTH (usually high) and cortisol levels (inappropriately low) to help make the diagnosis, but do not wait for the results to give steroids. The patient may die. Give prophylactic stress doses of corticosteroids in the setting of an illness, operation, or other stressor to prevent an adrenal crisis.

Only gold members can continue reading. Log In or Register to continue

Share this:

• Click to share on Twitter (Opens in new window)
• Click to share on Facebook (Opens in new window)

Related

Related posts:

1. Vascular Surgery
2. Cholesterol
3. Pulmonology
4. Gastroenterology

Stay updated, free articles. Join our Telegram channel

Join

Full access? Get Clinical Tree