Thyroid Basic and Clinical

Terms in this set (183)

b) C5 - T1

The thyroid is ensheathed by the ## pretracheal layer of deep cervical fascia.
The pretracheal fascia binds the thyroid to the trachea, and it moves with the trachea on swallowing.

## When there is thyroid enlargement, the attachment of the sternothyroid muscle to the trachea limits upward expansion of each lobe.

Inferior expansion may extend into the superior mediastinum, compressing the trachea and veins at the thoracic outlet

THE THYROID EXAM

• Look at the thyroid region. If the gland is quite enlarged, you may actually see it.

• To find the thyroid gland, first locate the thyroid cartilage (Adams Apple). This is a mid-line bulge towards the top of the anterior surface of the neck. The thyroid gland lies approximately 2-3 cm below the thyroid cartilage.

• If you're unsure, give the patient a glass of water and have them swallow as you watch this region. Thyroid tissue, along with all of the adjacent structures, will move up and down with swallowing. The normal thyroid is not visible. It is not worth going through this swallowing exercise if you don't see anything on gross inspection.

• Anterior palpation can be performed by using the thumb of one hand. Posterior palpation is done standing behind the seated patient with the tip of index, middle and ring fingers.

• If enlarged
o Is it symmetrically enlarged?
o Is the enlargement unilateral or bilateral?
o Are there discrete nodules within either lobe? If nodules are palpated, determine their shape, size, position, translucency, and consistency.
o If the gland feels firm, is it attached to the adjacent structures (i.e. fixed to underlying tissue, consistent with malignancy) or freely mobile (i.e., moves up and down with swallowing)?

• If there is concern regarding malignancy, a careful lymph node exam is important.

• A midline mass high in the neck, which rises further when the patient extends the tongue, is typical of a thyroglossal duct remnant or cyst.

• A systolic or continuous bruit over the thyroid suggests Graves' disease.
e) None

All these are causes of thyrotoxicosis, but not causes of hyperthyroidism

Thyrotoxicosis refers to the manifestations of excessive quantities of the thyroid hormones. The main causes of thyrotoxicosis are hyperthyroidism caused by Graves' disease, toxic multinodular goiter, and toxic adenomas.

## Thyrotoxicosis is not same as hyperthyroidism.

Hyperthyroidism is due to excessive thyroid function. Hyperthyroidism is thyrotoxicosis resulting from overproduction of hormone by the thyroid gland itself (e.g., Graves' disease). In thyroiditis (subacute or silent thyroiditis), presenting symptoms are those of thyrotoxicosis. Thyrotoxicosis in thyroiditis is due to the release of preformed thyroid hormones. True hyperthyroidism is absent since there is no overproduction of thyroid hormones. Radionuclide uptake is low in thyroiditis.

Thyrotoxicosis factitia is another cause of thyrotoxicosis with low or absent thyroid radionuclide uptake. Thyrotoxicosis factitia can be distinguished from thyroiditis by low levels of thyroglobulin.

Ectopic thyroid tissue, particularly teratomas of the ovary (struma ovarii ) and functional metastatic thyroid carcinoma also cause thyrotoxicosis with low or absent thyroid radionuclide uptake. Whole-body radionuclide studies can demonstrate ectopic thyroid tissue.

TYPES OF THYROTOXICOSIS


HYPERTHYROIDISM (RAIU increased except for iodine-induced hyperthyroidism)

1 Graves' disease
2 Toxic multinodular goiter
3 Toxic adenoma
4 Iodine-induced (Jod-Basedow)
5 Trophoblastic tumor
6 Increased TSH secretion



NO ASSOCIATED HYPERTHYROIDISM (RAIU decreased)

1. Thyrotoxicosis factitia
2. Subacute thyroiditis
3. hyroiditis with transient thyrotoxicosis
- Painless thyroiditis
- Silent thyroiditis
- Postpartum thyroiditis
4. Ectopic thyroid tissue
- Struma ovarii
- unfunctioning metastatic thyroid cancer
d) IV calcium
IV calcium is not indicated

Large doses of propylthiouracil should be given orally or by nasogastric tube or per rectum. Propylthiouracil is the agent of choice because it inhibits peripheral conversion of T 4 to T 3 in large doses.

## The major action of iodine is to inhibit hormone release.

Iodine acutely retards the rate of ## Secretion of T4. Iodine may also block thyroid hormone synthesis via the Wolff-Chaikoff effect (excess iodide transiently inhibits thyroid iodide organification).

## The rapid slowing of hormone release by iodine makes it more effective than the propylthiouracil when prompt relief of thyrotoxicosis is mandatory.

Iodine is given only one hour after the first dose of propylthiouracil. The 1-hour delay allows the antithyroid drug to prevent the excess iodine from being incorporated into new hormone. Iodine is also used in preparation for subtotal thyroidectomy, in severe thyrocardiac disease, and in acute surgical emergencies

Propranolol decreases tremulousness, palpitations, excessive sweating, eyelid retraction, and heart rate. High doses of propranolol decrease T 4 to T 3 conversion. Adrenergic antagonists are most useful in the interval when a response to thionamide or radioiodine therapy is being awaited.

Dexamethasone inhibits the secretion of thyroid hormone, inhibits the peripheral conversion of T4 to T3, and has immunosuppressive effects.

Concurrent administration of propylthiouracil, iodine, and dexamethasone to the patient with severe thyrotoxicosis causes a rapid reduction in serum T3 concentration. Additional therapeutic measures include antibiotics if infection is present, cooling, and intravenous fluids.
10) How does papillary carcinomas present?

a. Asymptomatic benign nodule [ Most papillary carcinomas present as an asymptomatic thyroid nodule. It moves freely during swallowing and is not distinguishable from a benign nodule.]

b. Enlarged cervical lymph node [ The first manifestation may be a mass in a cervical lymph node. Even with isolated cervical nodal metastases, prognosis is good.]

c. Hoarseness [ Hoarseness, dysphagia, cough, or dyspnea suggests advanced disease.]

d. Lung metastases [ In a minority of patients, hematogenous metastases are present at the time of diagnosis, most commonly in the lung.]

e. Any of the above T [ Papillary thyroid cancers have an excellent prognosis, with a 10-year survival rate > 95%.]


FINDINGS IN FAVOR OF MALIGNANT THYROID NODULES

Historical features

• Young (<20 years old) or old (>60 years old) age
• Male sex
• Neck irradiation during childhood or adolescence
• Rapid growth
• Symptoms of compression - Recent changes in speaking (hoarseness or dysphonia), breathing (dyspnea), or swallowing (dysphagia)
• Family history of thyroid malignancy



Physical examination

• Hard nodule
• Fixation to adjacent tissues
• Vocal cord paralysis
• Regional lymph adenopathy



Ultrasound findings

• Hypoechoic lesions
• Irregular margins
• Presence of calcifications
• Absence of halo
• Internal or central blood flow



High suspicion

• Family history of medullary thyroid carcinoma or multiple endocrine neoplasia

• Rapid tumor growth, especially during levothyroxine therapy

• Very firm or hard nodule

• Fixation of the nodule to adjacent structures

• Paralysis of vocal cords

• Regional lymphadenopathy

• Distant metastases
7) A 42-year-old woman presents with a palpable mass on the left side of her neck. She has no neck pain and no symptoms of thyroid dysfunction. Ultrasound examination reveals a solid, solitary, mobile thyroid nodule, 2 cm by 3 cm, without lymphadenopathy. The patient has no family history of thyroid disease and no history of external irradiation. What should be done?

a. Repeat ultrasonography after 1 year T [ The main concern is to exclude thyroid cancer. The initial evaluation should include measurement of the serum thyrotropin level and a fine-needle aspiration, preferably guided by ultrasonography. The usual approach after documenting benign cytology is to follow the patient yearly with neck palpation and measurement of the serum thyrotropin level, with repeated ultrasonography and fine-needle aspiration if there is evidence of growth of the nodule.]

b. Give levothyroxine [ Levothyroxine is not the recommended therapy to shrink or prevent growth of benign nodules because of the drug's low efficacy and potential side effects.]

c. Hemithyroidectomy [ In patients less than 20 years old, and in the case of a high clinical suspicion for cancer (e.g., follicular neoplasia as diagnosed by fine-needle aspiration and a nonfunctioning nodule revealed on scanning), the patient should be offered hemithyroidectomy regardless of the results of fine-needle aspiration.]

d. Iodine-131 [ In the case of a functioning benign nodule, iodine-131 is the therapy of choice, independent of concomitant hyperthyroidism.]
1) Amiodarone

a. High iodine levels persist for > 6 months even after discontinuation [ Amiodarone contains 40% of iodine by weight. Thus, typical doses of amiodarone (200 mg/d) are associated with very high iodine intake. Amiodarone is stored in adipose tissue. Therefore, high iodine levels persist for > 6 months after discontinuation of the drug.]

b. May cause hypothyroidism [ Excess iodide transiently inhibits thyroid iodide organification. This phenomenon is known as the Wolff-Chaikoff effect. In normal individuals, the thyroid gland escapes from this inhibitory effect and iodide organification resumes. The suppressive action of high iodide may persist in patients with underlying autoimmune thyroid disease. Amiodarone may cause hypothyroidism in such patients susceptible to the inhibitory effects of a high iodine load. Amiodarone-associated hypothyroidism is more common in women and individuals with positive TPO antibodies. It is usually unnecessary to discontinue amiodarone for this side effect. Levothyroxine can be used to normalize thyroid function.]

c. Amiodarone inhibits deiodinase activity [ Amiodarone first causes a transient decrease of T4 levels. This is due to Wolff-Chaikoff effect (i.e., the inhibitory effect of iodine on T4 release. Soon, most escape from this iodide-dependent suppression of the thyroid. Later, the inhibitory effects of amiodarone on deiodinase activity and thyroid hormone receptor action become predominant. This effects lead to increased T4, decreased T3, increased rT3, and a transient increase of TSH. TSH levels normalize or are slightly suppressed after about 1 to 3 months.]

d. May cause thyrotoxicosis [ Jod - Basedow phenomenon is thyroid hormone synthesis becoming excessive as a result of increased iodine exposure. Amiodarone-induced thyrotoxicosis is far more prevalent in iodine-deficient regions.]

e. All of the above T [ Amiodarone may also cause a thyroiditis-like condition.]
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