Overactive Thyroid

Understanding an Overactive Thyroid

The thyroid gland is the small butterfly-shaped endocrine gland located at the anterior section of the lower neck, just beneath the larynx. This small gland is vital to the overall growth and metabolism of the body, keeping a very active role in maintaining homeostasis.

The lobes of the thyroid are composed of follicles, small spherical sacs that are made up of follicular cells containing the enzymes necessary for thyroglobulin synthesis along with the enzymes essential for the release of thyroid hormones. The thyroglobulin forms the basic structure of the two types of thyroid hormones, Triiodothyronine (T3) and thyroxine (T4). Both these hormones are formed from two molecules of amino acid tyrosine (thyronine) and iodine. The absence of tyrosine and iodine in the diet inhibits the production of these two hormones.

Both these hormones are needed for cellular respiration, carbohydrate synthesis and the formation of lipid and its metabolism. Production and release of these two hormones are regulated by other hormones secreted by the pituitary gland (thyroid-stimulating hormone, TSH) and the hypothalamus (thyrotropin-releasing hormone, TRH), through the negative feedback mechanism. Decrease blood levels of the thyroid hormones activate the hypothalamus to release TRH which then stimulates the pituitary gland to secrete TSH. Once the body sends signals (TSH) for its use, the thyroglobulin is reabsorbed into the follicular lumen and broken down into triidothyronine and thyroxine and released into the system, bringing their levels back to normal.

Overactive Thyroid Gland:  Hyperthyroidism

Hyperthyroidism is basically on overactive thyroid gland that produces too much amounts of thyroid hormones. The excessive levels of these hormones in the blood increase the metabolic rate of the body resulting to rapid and irregular heart rate, sweating, sudden loss of weight and irritability or nervousness.

This condition is more prevalent in women (1:500) than in men (1:500) and can develop at any age. There are many factors that can cause this condition. One of these is Grave’s disease, an autoimmune disease where an antibody stimulates the production and secretion of thyroid hormones. This problem is normally hereditary and often affects the women more.

Another cause of an overactive thyroid is thyroiditis or the swelling of the thyroids, usually due to viral infections or post-pregnancy inflammatory processes. The distension causes some of the thyroid hormones to leak out into the bloodstream. Hypothyroidism occurs after awhile when the stored hormones levels are depleted. Due to the negative feedback mechanism, the gland functions are restored to its normal state. Other causes include abnormal iodine intake, thyroid nodules, radiation exposure and a hyper pituitary gland that increases the stimulation of the thyroid.

Incidence of Grave’s disease in Asians, Hispanics and Caucasians are the same but occurs less frequently among the black race. Most individuals between the ages 20 and 40 have increase incidence of this problem. Toxic adenomas occur more frequently among the younger population whereas toxic multinodular goiters are common among individuals 50 years old and above.

Hyperthyroidism can be diagnoses through blood tests, where the levels of T3 and T4 are measured. Normal blood levels of free T4 is 0.8 -1.7 mcg/dl, whereas T3 is around 97 -219 mcg/dl. Any values higher that this should be checked properly.

Aside from blood tests, thyroid function can also be tested using the Iodine Uptake Scan. This test would determine the amount of iodine that can be absorbed by the thyroid gland. Together with this diagnostic test is the thyroid scan where a complete picture of the gland is seen through the emissions of the radioactive iodine.

Overactive Thyroid Symptoms

Signs of overactive thyroid

Initially people with an overactive thyroid gland will not experience any of the symptoms until its advanced stages.  Symptoms of overactive thyroid include:

  • Insomnia
  • heat intolerance
  • increased appetite but still experiences weight loss
  • tremors
  • palpitations (increased heart rate)
  • diarrhea
  • fine hair
  • goiter (enlargement of the thyroid)
  • irritability
  • nervousness
  • fatigue
  • decreased concentration
  • shortness of breath during exertion
  • excessive tears
  • photophobia
  • exopthalmus
  • pretibial myxedema

These symptoms (overactive thyroid) occur as a result to the increased production and secretion of thyroid hormones leading to an increase in the metabolic rate of the body. Some of the symptoms may mimic other diseases, so make sure to see a physician for proper diagnosis and treatment. Delayed treatment may cause complications that might be fatal.

Overactive thyroid symptoms in women

This condition is more prevalent in women between the age groups of 30 and 40. The common causes of this problem in women are Grave’s disease and pregnancy. Symptoms of overactive thyroid may differ from one person to another but most women would experience the following, aside from the usual symptoms (overactive thyroid):

  • Hot flashes
  • Osteoporosis
  • Irregular menses
  • Difficulty in conceiving
  • Decrease in libido

Overactive Thyroid in Men and Women

Women are more prone to an overactive thyroid then men. According to the survey done by BUPA, one out of fifty women is more likely to contract this disease condition compared to one of five hundred in men.

Although both men and women may the have the same symptoms of overactive thyroid, they differ in the way symptoms are manifested. An overactive thyroid in men could lead to weakness and muscle wasting in the upper arms and thigh areas. The degree of fatigue and exhaustion may not be the same as that of women but would manifest changes in appetite, weight gain and loss of memory. Aside from that they could experience a decrease libido, breast tenderness and enlargement due to low levels of testosterone that could cause self-esteem issues.

Overactive Thyroid Treatment

The objective of the treatment plans is to return the thyroid gland to its euthyroid (normal) state thus decreasing or eliminating the symptoms felt by clients. There are many treatment plans available and since the thyroid hormone levels will not immediately decline, the symptoms are also treated to prevent further complications.

Tachycardia (rapid heart rate) is often treated first. Clients are often given beta-blockers (propanolol, atenolol and metropolol) to slow down the heart rate but these medications will not change the blood levels of the thyroid hormones. Aside from decreasing the heart rate, these medications would also help relieve anxiety and tremors.

The two most common overactive thyroid medications are methimazole and propylthiouracil (PTU). These drugs would suppress the production of thyroid. PTU would also inhibit the conversion of T4 to T3, the more active hormone. High starting doses (loading doses) of these drugs are given and eventually decreased based on the lab results. The effects are usually seen six to twelve weeks after initial dose. Although the levels of thyroid hormones are decreased, most of the clients will need to maintain the intake of these medications up to a year or more depending on the severity of the disease. Keep in mind also that PTU would cause suppression of WBC, therefore constant monitoring is required. Symptoms like fever and sore throat should be reported immediately.

The option to use PTU or methimazole is subjective. The drug methimazole is more potent and effects last longer with better compliance rate among patients. PTU is the considered the drug of choice for patients experiencing serious thyrotoxicosis since it inhibits the conversion of T4 to T3. Thyrotoxic symptoms are resolved more quickly if T3 levels are reduced. The problem with PTU, aside from decreasing WBC count, is its higher hepatotoxic effects which prompted the FDA to place boxed warnings on its packaging – this considered to be the highest warning level of the FDA.

Radioactive iodine is also given in some cases. Since iodine is taken up by the thyroid gland, the radioactive iodine will be deposited there. The radioactivity would destroy some of the thyroid cells thus reducing the source of production. The effects of this therapy (euthyroid) would be observed after eight to twelve weeks. The complication here, and as with oral antithyroids, is the development of hypothyroidism. Make sure to have regular thyroid panel checks to determine levels and avoid this problem. Patients undergoing this therapy have to be hospitalized for proper monitoring. After the treatment, individuals should avoid getting pregnant for at least six months. Avoid also going near young children and infants for at two to four days after treatment. Radiation alarms in airports might be triggered therefore make sure to bring a medical certificate describing the treatment procedure.

The most invasive treatment option is surgery where the thyroids are removed either the whole gland (thyroidectomy) or a portion of it (partial thyroidectomy). Although the chances of permanently controlling the condition is high (90%), there is still a possible complication that needs to be considered. Above the thyroid gland is a very small organ called parathyroid which is responsible for controlling the calcium levels of the blood. During thyroidectomy, there is an increase chance of accidental removal of this gland thus causing abnormalities in the serum calcium levels. Another complication, although very rare, is the chance of developing vocal cord paralysis. This treatment plan is ideal for pregnant women who have adverse reactions to antithyroid hormones and are not qualified to take in radioactive iodine. Patients with very large thyroids, especially where surrounding tissues are already compressed, also need to undergo this treatment.
References:

  1. http://www.ncbi.nlm.nih.gov/books/NBK28/
  2. http://www.medicinenet.com/hyperthyroidism/article.htm
  3. http://www.emedicinehealth.com/hyperthyroidism/article_em.htm
  4. http://www.mayoclinic.com/health/hyperthyroidism/DS00344



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