Hyperthyroidism is the medical term for overactivity of thyroid gland leading to increased production and secretion of the thyroid hormones. The condition is also referred to as thyrotoxicosis referring to the abnormally high levels of the thyroid hormones in the circulation. Common symptoms include drastic loss of body weight, increased heart rate and irritability. Untreated hyperthyroidism may lead to number of complications like heart failure, weak bones and rarely a thyrotoxic crisis. Usually antithyroid drugs and radioactive iodine are sufficient to manage the condition, however surgical removal of the gland is sometimes required.
Hyperthyroidism can be asymptomatic. When it is symptomatic, it can present with a number of symptoms like :
- Drastic weight loss although appetite is normal or increased.
- Palpitation (tachycardia).
- Nervousness, anxiety, poor concentration and restlessness.
- Intolerance to heat.
- Profuse sweating.
- Irregular menstrual cycle.
- Breast enlargement in men.
- Hair loss.
- Hand tremors.
- Itchy skin.
- Nausea and vomiting.
In elderly patients symptoms of hyperthyroidism are not easy to identify. In rare cases the eyes may be affected due to swelling of the tissues and muscles behind the eyes leading to :
- Protrusion of eyes.
- Red, puffy eyes.
- Sensitivity to light (photophobia), increased tear production.
- Double vision and blurring of vision.
Thyroid crisis (thyrotoxic crisis) is a rare complication of hyperthyroidism characterized by high fever, vomiting, diarrhea, dehydration, increased pulse rate, coma even death. It requires immediate medical attention.
The thyroid gland is a butterfly shaped organ situated at the base of the neck and produces the hormones namely T3 (triiodothyronine), T4 (thyroxine) and calcitonin.The main physiological functions of thyroid hormones are control of fat, carbohydrate and protein metabolism, maintenance of body temperature, mental and physical growth and development. Calcitonin maintains the circulating calcium level.
The hypothalamus and pituitary gland are the principal organs regulating secretion of thyroid hormones. The hypothalamus produces TRH (thyroid releasing hormone) to stimulate the pituitary to produce TSH (thyroid stimulating hormone). TSH then stimulates the thyroid gland to secrete thyroid hormones.
In turn, thyroid hormones regulate the activity of TRH and therefore TSH in a feedback mechanism. Thus excess thyroid hormone inhibits TSH production from pituitary leading to suppression of thyroid function and prevents a further rise in thyroid hormone levels. This regulatory system does not function properly in hyperthyroidism.
Common causes include :
- Graves’ disease is an autoimmune disease where antibodies mistakenly stimulate the thyroid gland to produce excessive T4.
- Toxic adenoma and toxic multi nodular goiter (Plummer’s disease) are non-cancerous tumors of the thyroid gland leading to increased production of thyroid hormones.
- Thyroiditis is a condition where there is inflammation of the gland causing release of excess thyroid hormone stored in the gland. It may occur in women after delivery (postpartum thyroidtis)
Women are at a greater risk of hyperthyroidism. A family history of Grave’s disease is a major risk factor among first-degree relatives.
In some cases, hyperthyroidism may resolve on its own but this is rare.
- Anti thyroid drugs, such as propylthiouracil and methimazole, acts by suppressing thyroid hormone synthesis. Usually it takes 6 to 12 weeks to show any improvement.
- Radioactive iodine destroys the thyroid gland and is not to be given in young or pregnant patients.
- Surgery nay be necessary to remove the thyroid gland (thyroidectomy).