Atlas of pathophysiology, 2 Edition

Part II - Disorders

Endocrine Disorders

Thyroid Cancer

Thyroid carcinoma is the most common endocrine malignancy. It occurs in all age groups, especially in people who have had radiation treatment of the neck area.

Causes

Direct cause unknown

Predisposing factors

·   Prolonged thyroid-stimulating hormone stimulation due to radiation exposure or heredity

·   Familial predisposition

·   Chronic goiter

Pathophysiology

Papillary carcinoma accounts for half of all thyroid cancers in adults. Most common in young adult females, it's the least virulent form of thyroid cancer and metastasizes slowly.Follicular carcinoma is less common but more likely to recur and metastasize to the regional nodes and through blood vessels into the bones, liver, and lungs. Medullary carcinomaoriginates in the parafollicular cells derived from the last branchial pouch and contains amyloid and calcium deposits. It can produce thyrocalcitonin, histaminase, adrenocorticotropin (producing Cushing's syndrome), and prostaglandin E2 and F3 (producing diarrhea). This rare form of thyroid cancer is familial, associated with pheochromocytoma, and completely curable when detected before it causes symptoms. Untreated, it progresses rapidly. Seldom curable by resection, anaplastic tumors resist radiation and metastasize rapidly.

Signs and symptoms

·   Painless nodule; hard nodule in an enlarged thyroid gland; or palpable lymph nodes and thyroid enlargement

·   Hoarseness, dysphagia, dyspnea, pain on palpation

·   Cough

·   Hypothyroidism (low metabolism, mental apathy, sensitivity to cold) or hyperthyroidism (hyperactivity, restlessness, sensitivity to heat)

·   Diarrhea, anorexia, irritability, vocal cord paralysis

·   Symptoms of distant metastasis

Diagnostic test results

·   Calcitonin assay identifies silent medullary carcinoma; calcitonin level measuring during a resting state and during a calcium infusion (15 mg/kg over a 4-hour period) showing an elevated fasting calcitonin level and an abnormal response to calcium stimulation—a high release of calcitonin from the node in comparison with the rest of the gland—indicates medullary cancer.

·   Thyroid scan differentiates functional nodes, which are rarely malignant, from hypofunctional nodes, which are commonly malignant.

·   Ultrasonography shows changes in the size of thyroid nodules after thyroxine suppression therapy and is used to guide fine-needle aspiration and to detect recurrent disease.

·   Magnetic resonance imaging and computed tomography scans provide a basis for treatment planning because they establish the extent of the disease within the thyroid and in surrounding structures.

·   Fine-needle aspiration biopsy differentiates benign from malignant thyroid nodules.

·   Histologic analysis stages the disease and guides treatment plans.

Treatment

·   Papillary or follicular cancer—total or subtotal thyroidectomy; modified node dissection (bilateral or unilateral) on the side of the primary cancer

Clinical Tip

Before surgery, tell the patient to expect temporary voice loss or hoarseness lasting several days after surgery.

·   Medullary, giant, or spindle cell cancer—total thyroidectomy and radical neck excision

·   Inoperable cancer or postoperatively in lieu of radical neck excision—radiation (131I) or external radiation

·   To increase tolerance to surgery and radiation—adjunctive thyroid suppression with exogenous thyroid hormones and simultaneous administration of an adrenergic blocking agent such as propranolol

·   Metastasis — 131I; chemotherapy for symptomatic, widespread metastasis is rare

Clinical Tip

Hypocalcemia may develop if parathyroid glands are removed during surgery.

·   Thyroid hormone replacement after surgeries

P.297

EARLY, LOCALIZED THYROID CANCER

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