HYPERTHYROIDISM (THYROTOXICOSIS)

 

Hyperthyroidism, also called thyrotoxicosis, is a hypermetabolic clinical and biochemical state caused by excess production of thyroid hormones. The condition is more frequent in females and is associated with rise in both T3 and T4 levels in blood, though the increase in T3 is generally greater than that of T4.

 

Causes.

 

Hyperthyroidism may be caused by many diseases but three most common causes are: Graves’ disease (diffuse toxic goitre), toxic multinodular goitre and a toxic adenoma. Less frequent causes are hypersecretion of pituitary TSH by a pituitary tumour, hypersecretion of TRH, thyroiditis, metastatic tumours of the thyroid, struma ovarii, congenital hyperthyroidism in the newborn of mother with Graves’ disease, hCG-secreting tumours due to mild thyrotropic effects of hCG (e.g. Hydatidiform mole, choriocarcinoma and testicular tumours), and lastly, by excessive doses of thyroid hormones or iodine called jodbasedow disease.

 

Features.

 

Patients with hyperthyroidism have a slow and insidious onset, varying in severity from case to case. The usual symptoms are emotional instability, nervousness, palpitation, fatigue, weight loss in spite of good appetite, heat intolerance, perspiration, menstrual disturbances and fine tremors of the outstretched hands. Cardiac manifestations in the form of tachycardia, palpitations and cardiomegaly are invariably present in hyperthyroidism. The skin of these patients is warm, moist and flushed. Weakness of skeletal muscles and osteoporosis are common. Typical eye changes in the form of exophthalmos are a common feature in Graves’ disease. Serum levels of T3 and T4 are elevated but TSH secretion is usually inhibited. A sudden spurt in the severity of hyperthyroidism termed ‘thyroid storm’ or ‘thyroid crisis’ may occur in patients who have undergone subtotal thyroidectomy before adequate control of hyperthyroid state, or in a hyperthyroid patient under acute stress, trauma, and with severe infection. These patients develop high grade fever, tachycardia, cardiac arrhythmias and coma and may die of congestive heart failure or hyperpyrexia.

 

Treatment.

 

There are readily available and effective treatments for all common types of hyperthyroidism.

Anti-thyroid Drugs

Two common drugs in this category are methimazole and propylthiouracil (PTU), both of which actually interfere with the thyroid gland's ability to make its hormones. The illustration shows that some hormone is made, but the thyroid becomes much less efficient. When taken faithfully, these drugs are usually very effective in controlling hyperthyroidism within a few weeks.

Anti-thyroid drugs can have side effects such as rash, itching, or fever, but these are uncommon. Very rarely, patients treated with these medications can develop liver inflammation or a deficiency of white blood cells therefore, patients taking antithyroid drugs should be aware that they must stop their medication and call their doctor promptly if they develop yellowing of the skin, a high fever, or severe sore throat. The main shortcoming of antithyroid drugs is that the underlying hyperthyroidism often comes back after they are discontinued. For this reason, many patients with hyperthyroidism are advised to consider a treatment that permanently prevents the thyroid gland from producing too much thyroid hormone.

Radioactive Iodine Treatment



Radioactive iodine is the most widely-recommended permanent treatment of hyperthyroidism. This treatment takes advantage of the fact that thyroid cells are the only cells in the body which have the ability to absorb iodine. In fact, thyroid hormones are experts at doing just that.



By giving a radioactive form of iodine, the thyroid cells which absorb it will be damaged or killed. Because iodine is not absorbed by any other cells in the body, there is very little radiation exposure (or side effects) for the rest of the body. Radioiodine can be taken by mouth without the need to be hospitalized. This form of therapy often takes one to two months before the thyroid has been killed, but the radioactivity medicine is completely gone from the body within a few days. The majority of patients are cured with a single dose of radioactive iodine.



The only common side effect of radioactive iodine treatment is underactivity of the thyroid gland. The problem here is that the amount of radioactive iodine given kills too many of the thyroid cells so that the remaining thyroid does not produce enough hormone, a condition called hypothyroidism.There is no evidence that radioactive iodine treatment of hyperthyroidism causes cancer of the thyroid gland or other parts of the body, or that it interferes with a woman's chances of becoming pregnant and delivering a healthy baby in the future. It is also important to realize that there are different types of radioactive iodine (isotopes). The type used for thyroid scans (iodine scans) as shown in the picture below give up a much milder type of radioactivity which does not kill thyroid cells.

Surgical Removal of the Gland or Nodule

Another permanent cure for hyperthyroidism is to surgically remove all or part. Surgery is not used as frequently as the other treatments for this disease. The biggest reason for this is that the most common forms of hyperthyroidism are a result of overproduction from the entire gland (Graves' disease) and the methods described above work quite well in the vast majority of cases.



Although there are some Graves' disease patients who will need to have surgical removal of their thyroid (cannot tolerate medicines for one reason or another, or who refuse radioactive iodine), other causes of hyperthyroidism are better suited for surgical treatment earlier in the disease.



One such case is illustrated here where a patient has hyperthyroidism due to a hot nodule in the lower aspect of the right thyroid lobe. Depending on the location of the nodule, the surgeon can remove the lower portion of the lobe as illustrated on the left, or he/she may need to remove the entire lobe which contains the hot nodule as shown in the second picture. This should provide a long term cure.



Concerns about long hospitalizations following thyroid surgery have been all but alleviated over the past few years since many surgeons are now sending their patients home the morning following surgery (23 hour stay). This, of course, depends on the underlying health of the patient and their age, among other factors. Some are even treating partial thyroidectomy as an out-patient procedure where healthy patients can be sent home a few hours after the surgery. Although most surgeons require that the patient be put to sleep for operations on the thyroid gland, a some are even removing one side of the gland under local anesthesia with the aid of IV sedation. These smaller operations tend to be associated with fewer complaints.


A potential down side of the surgical approach is that there is a small risk of injury to structures near the thyroid gland in the neck including the nerve to the voice box (the recurrent laryngeal nerve). The incidence of this is about 1%. Like radioactive iodine treatment, surgery often results in hypothyroidism. This fact is obvious when the entire gland is removed, but it may occur following alobectomy as well.

Whenever hypothyroidism occurs after treatment of an overactive thyroid gland, it can be easily diagnosed and effectively treated with levothyroxine. Levothyroxine fully replaces thyroid hormones deficiency and, when used in the correct dose , can be safely taken for the remainder of a patient's life without side effects or complications. Just one small pill per day.