What is Hyperthyroidism?
Thyroid hormone overproduction results in the metabolic imbalance hyperthyroidism, which is also called thyrotoxicosis. There are several types of hyperthyroidism.
The most common form of hyperthyroidism is Graves' disease, which increases thyroxine (T4) production, enlarges the thyroid gland (goiter), and causes multiple systemic changes. The incidence of Graves' disease is highest between ages 30 and 60, especially in people with family histories of thyroid abnormalities; only 5% of hyperthyroid patients are younger then age 15. With treatment, most patients can lead normal lives. However, thyrotoxic crisis or thyroid storm, an acute exacerbation of hyperthyroidism, is a medical emergency that can lead to life-threatening cardiac, hepatic, or renal failure.
Causes of Hyperthyroidism
Hypothyroidism may result from genetic and immunologic factors. In Graves' disease, thyroid-stimulating antibodies bind to and then stimulate the thyroid stimulating hormone (TSH) receptors of the thyroid gland. The trigger for this autoimmune disease is unclear. The increased incidence of the disease among monozygotic twins points to an inherited factor, probably with a polygenic inheritance pattern. Graves' disease occasionally coexists with other autoimmune endocrine abnormalities, such as diabetes mellitus, thyroiditis, and hyperparathyroidism. It's also associated with the production of autoantibodies (long-acting thyroid Stimulator [LATS], LATS-protector, and human thyroid adenyl cyclase stimulator), possibly caused by a defect in suppressor -T-lymphocyte function that allows the formation of these autoantibodies.
In a person with latent hyperthyroidism. excessive intake of iodine and, possibly, stress can precipitate clinical hyperthyroidism. Similarly, in a person with inadequately treated hyperthyroidism, stressful conditions, such as surgery, infection, toxemia of pregnancy, and diabetic ketoacidosis, can precipitate thyrotoxic crisis.
Signs & Symptoms of Hyperthyroidism
Note that Hyperthyroidism symptoms usually refers to various symptoms known to a patient, but the phrase Hyperthyroidism Signs may refer to those Signs only noticable by a doctor:
The following laboratory tests confirm the diagnosis of hyperthyroidism: Radioimmunoassay shows increased serum triiodothyronine (T3) and T4 concentrations, thyroid scan reveals increased uptake of radioactive iodine (¹³¹I) (This test is contraindicated in pregnant patients.), and thyrotropin-releasing hormone (TRH) stimulation test helps to confirm a diagnosis of hyperthyroidism if the TSH level fails to increase within 30 minutes after administration of TRH.
Other supportive test results show increased serum protein-bound iodine and decreased serum cholesterol and total lipid levels. Ultrasonography confirms subclinical ophthalmopathy.
In hyperthyroidism, treatment consists of drugs, radioiodine, and surgery. Antithyroid drug therapy is used for children, young adults, pregnant women, and patients who refuse surgery or radioiodine treatment. Thyroid hormone antagonists include propylthiouracil(PTU) and methimazole, which block thyroid hormone synthesis.
Although hypermetabolic symptoms subside within 4 to 8 weeks after therapy begins, the patient must continue taking the medication for 6 months to 2 years. In many patients, concomitant propranolol is used to manage tachycardia and other peripheral effects of excessive sympathetic activity.
During pregnancy, antithyroid medication should be Kept at the minimum dosage required to maintain normal maternal thyroid function and to minimize the risk of fetal hypothyroidism, even though most infants of hyperthyroid mothers are born with mild and transient hyperthyroidism. (Neonatal hyperthyroidism may even require treatment with antithyroid drugs and propranolol for 2 to 3 months.) Because exacerbation of hyperthyroidism sometimes occurs in the puerperium, continuous control of maternal thyroid function is essential. About 3 to 6 months postpartum, antithyroid drugs can be gradually decreased and thyroid function reassessed (drugs may be discontinued at that time). Mothers shouldn't breast-feed during treatment with antithyroid drugs because this can cause neonatal hypothyroidism.
Treatment with ¹³¹I consists of a single oral dose and is the treatment of choice for women past reproductive age or men and women not planning to have children. (Patients of reproductive age must give informed consent for this treatment because small amounts of ¹³¹I concentrate in the gonads.) During treatment, the thyroid gland picks up the radioactive element as it would regular iodine. Subsequently, the , radioactivity destroys some of the cells that normally concentrate iodine and produce T4, thus decreasing thyroid hormone production and normalizing thyroid size and function. In most patients, hypermetabolic symptoms diminish within 6 to 8 weeks after such treatment. However, some patients require a second dose.
Subtotal (partial) thyroidectomy is indicated for the patient under age 40 who has a very large goiter and whose hyperthyroidism has repeatedly relapsed after drug therapy. This surgery involves removing part of the thyroid gland, decreasing its size and capacity for hormone production. Preoperatively, the patient may receive iodides (Lugol's or potassium iodide solution), antithyroid drugs, or high doses of propranolol to help prevent thyroid storm. If euthyroidism isn't achieved, surgery should be delayed and propranolol should be administered to decrease the risk of cardiac arrhythmias that are caused by hyperthyroidism.
Therapy for hyperthyroid ophthalmopathy includes local applications of topical medications but may require high doses of corticosteroids. A patient with severe exophthalmos that causes pressure on the optic nerve may require surgical decompression to lessen pressure on the orbital contents.
Treatment of thyrotoxic crisis includes administration of an antithyroid drug such as PTU, I.V. propranolol to block sympathetic effects, a corticosteroid to inhibit the conversion of T3 to T4 and to replace depleted cortisol, and an iodide to block release of the thyroid hormones. Supportive measures include nutrients, vitamins, fluid administration, and sedatives as necessary.
There are no known prevention methods for hyperthyroidism, since its causes are either inherited or not completely understood. Knowledge of family history and close attention to symptoms and Signs of the disease this is best prevention tactic. Careful attention to prescribed therapy can prevent complications of the disease.
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