Hyperthyroidism

Hyperthyroidism is characterized by the activation of sympathetic nervous system [3]. The common symptoms of hyperthyroidism include:

• Weight loss with increased appetite
• Increased sweating
• Heat intolerance
• Anxiety and nervousness
• Palpitations
• Irritability
• Muscle weakness and easy fatigability
• Menstrual abnormalities
• Changes in bowel patterns
• Fine tremors in the patient’s hands and feet

Older adults usually either have no symptoms, or have only subtle ones such as increased heart rate, easy fatigability and heat intolerance.

In addition to complete history, examination and base-line investigations, the following specific set of investigations are helpful in establishing the diagnosis of any thyroid disease [4].

• Serum T3 an T4 levels
• Serum TSH levels
• Iodine uptake
• Thyroid scan
• Ultrasonography

In case of auto-immune thyroiditis, the most specific auto-antibody test is an ELISA (Enzyme Linked Immunosorbent Assay) test for anti-thyroid peroxidase antibody. The titres are significantly increased in case of Grave’s hyperthyroidism, but are very low or absent in case of toxic adenoma or toxic multi-nodular goiter.

Hyperthyroidism is managed by providing symptomatic relief and anti-thyroid therapy, which includes anti-thyroid drugs, radio-active iodine-131 or thyroidectomy.

Anti-thyroid drugs

The drugs commonly used are carbimazole, and propylthiouracil. Both of these drugs interfere with the oxidation of iodides and binding of iodine to tyrosine [5] [6]. 

Advantages:

• No surgery required
• No use of radioactive iodine

Disadvantages:

• Treatment is prolonged (6-24 months)
• Failure rate is 50% and relapses may occur [7]
• Very dangerous side-effect such as agranulocytosis, aplastic anemia and oropharyngeal bacterial infection can occur and may require discontinuation of the drug

Surgery

In toxic and nodular goiter surgery, subtotal or total thyroidectomy cures the disease by reducing the mass of overactive tissue [8]. 

Advantages:

• Cure is rapid
• Cure rate is high

Disadvantages:

• Risk of hypoparathyroidism (5%) [9]
• Risk of recurrent laryngeal nerve injury
• Recurrence of thyrotoxicosis in 5% of patients who were subjected to subtotal thyroidectomy

Radioactive iodine (RAI)

Radioiodine destroys the thyroid cells without surgery. In this treatment, radioactive iodine is given orally which is taken up by the follicles. In the thyroid follicles, beta and gamma rays are emitted from the radioactive iodine which destroys the follicles [10].

Advantages:

• No surgery
• No prolonged drug treatment

Disadvantages:

• Late hypothyroidism

Contraindications:

• Absolute contraindications are pregnancy and breast feeding.
• Relative contraindications include young age, multi-nodularity and Grave’s opthalmopathy.

Hyperthyroidism resulting from toxic multi-nodular goiter and toxic adenoma mostly occurs in adults and remains throughout life. Long term high-dose anti-thyroid drugs are not recommended after the person becomes euthyroid. Instead, radio-active iodine ablation is recommended. Increased thyroid hormone causes left ventricular thickening that results in an increased risk of cardiac death and other cardiac problems. Eye problems usually improve after proper treatment.

Hyperthyroidism can result from several different causes that are listed below [1].

• Graves disease: It has an autoimmune etiology and is characterized by the presence of auto-antibodies that are capable of stimulating the thyroid gland.
• Toxic multinodular goiter: 60% of the cases of toxic multinodular goiter are caused by defects in the TSH (thyroid stimulating hormone) receptor gene. In 40% of the cases, the cause is unknown.
• Toxic adenoma: Toxic adenoma of the thyroid gland is caused by a point mutation in the TSH (thyroid stimulating hormone) receptor gene.
• Thyroiditis: Different types of thyroiditis have their own etiologies. Hashimoto's thyroiditis has an autoimmune basis whereas De Quervian thyroiditis has a genetic predisposition in specific human leukocyte antigens (HLAs). Suppurative thyroiditis is caused by infections. Drugs such as lithium, amiodarone and interferon-alpha can also cause the development of thyroiditis.

In the United States, the most commonly occurring form of hyperthyroidism is Grave’s disease. It constitutes around 60 to 80% of the total cases. The peak occurrence is in people with ages 20 to 40.

In iodine-deficient areas, the most common type is toxic multi-nodular goiter, comprising up to 15 to 20% of total cases. It typically presents in people older than 50 years of age.

Thyroid hormone secretion is controlled by a complex feed-back mechanism which involves stimulatory and inhibitory factors. The hypothalamus releases thyrotropin-releasing hormone (TRH) which stimulates the pituitary gland to release thyroid stimulating hormone (TSH). Thyroid stimulating hormone in turn causes the release of T3 and T4 from the thyroid gland. Increased levels of T3 and T4 decrease the production of TSH by negative feed-back mechanism.

Any pathology involving the pituitary gland, thyroid or in the periphery leading to increased levels of circulating thyroid hormone results in thyrotoxicosis. Regardless of where the pathology lies, the result is an increase in the transcription of the cellular proteins which then leads to the increased basal metabolic rate [2].

There are no current guidelines on the prevention of hyperthyroidism. Hyperthyroidism caused by Grave’s disease cannot be prevented as it is genetically mediated. However, people residing in iodine deficient areas must introduce iodine in their diets to prevent the occurrence of toxic multi-nodular goiter which is most likely to occur in such areas. This might greatly affect the over-all incidence of hyperthyroidism in these areas.

Also, people with a positive family history of hyperthyroidism or those residing in iodine deficient areas should get themselves periodically checked up for early diagnosis and treatment.

Hyperthyroidism is a term reserved for disorders that result in the overproduction of the thyroid hormone by the thyroid gland. Thyrotoxicosis is a term used to describe a state of thyroid hormone excess resulting from any source. The most common cause of thyroid hormone excess is Graves disease. Toxic multinodular goiter is the second most common cause.

Hyperthyroidism refers to the condition in which the levels of thyroid hormone in the body are high. This leads to a wide range of symptoms including weight loss, increased appetite, increased sweating, intolerance to heat, anxiety and irritability. Hyperthyroidism can be treated by drugs, surgery or radiation.

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