The thyroid gland plays an important role in maintaining the body’s metabolism by secreting two hormones, T3 (triiodothyronine) and T4 (thyroxine), Certain diseases however may upset the functioning of the thyroid gland, resulting in high levels of thyroid hormones (hyperthyroidism) or low levels of thyroid hormones (hypothyroidism). The prevalence of hypothyroidism is growing globally and one of the most common causes is an autoimmune condition known as Hashimoto’s thyroiditis (discussed below).
Thyroid Gland & Hormones
The thyroid gland is located in the neck, slightly below the Adam’s apple and is controlled by the pituitary gland. When the thyroid gland needs to be stimulated, the pituitary gland secretes thyroid stimulating hormone (TSH). The pituitary gland controls the level of thyroid stimulation based on the levels of thyroid hormones (T3 and T4) in the blood. If the thyroid hormones are low, then the pituitary gland will secrete more TSH and if T3 and T4 levels in the blood are too high, then pituitary gland secretes less TSH. The pituitary gland does not act alone and it controlled by the hypothalamus, which secretes thyrotropin-releasing hormone (TRH). TRH acts on the pituitary gland to trigger more TSH release. This entire cycle is delicately balanced to maintain stable levels of thyroid hormones (T3 and T4) in the blood and is known as the feedback effect.
Signs & Symptoms of Hypothyroidism
- Fatigue and lethargy
- Moderate weight gain
- Sensitivity to cold
- Pale skin
- Muscle aches and body pains
- Changes in menstruation in women and hypothyroidism may be one of the causes of infertility.
Causes of Hypothyroidism
A number of conditions can cause an underactive thyroid gland but these should only be diagnosed with proper testing by a medical doctor. Hypothyroidism should not be confused with obesity, which may present with similar signs and symptoms, although obesity is a result of excessive calorie intake from food with low activity levels.
Causes of hypothyroidism include :
- Hashimoto’s thyroiditis
- Thyroid hormone drugs & other medication
- Radiation therapy for cancer
- Surgical thyroid removal
- Pituitary gland disorders
- Congenital diseases (present from birth)
- Iodine deficiency
Some conditions may also cause low thyroid hormone levels, although the thyroid gland and the feedback effect is functioning properly. This is known as euthyroid sick syndrome and may be caused by fasting, starvation, certain diets, malnutrition, kidney failure, myocardial infarction (heart attack), cirrhosis (liver disease often related to alcoholism), diabetes, trauma or sepsis.
Hashimoto’s thyroiditis is an autoimmune disease affecting the thyroid gland and is one of the most common causes of hypothyroidism. It is more prevalent in women, although men may also be affected, and occurs as a result of your body’s immune system ‘attacking’ your thyroid gland. This causes inflammation of the thyroid gland, which is then unable to produce and secrete the thyroid hormones, T3 and T4. Hashimoto’s thyroiditis will present with the hypothyroidism symptoms in addition to a slight swelling of the thyroid gland, which is usually not tender or painful.
In order to diagnose hypothyroidism, your doctor may request a series of thyroid hormone blood tests, sometimes referred to as a thyroid profile. These tests will measure the level of thyroid hormones in the blood, either as total or free T3 and T4, with the latter referring to unbound thyroid hormones in circulation. Your TSH levels may also be checked to verify if the cause of your underactive thyroid is a result of reduced stimulation by the pituitary gland.
A thyroid antibody test is necessary in a case of Hashimoto’s thyroiditis as these antibodies indicate immune activity against the thyroid gland. In certain cases where the cause cannot be isolated, your doctor may consider testing for thyrotropin-releasing hormone (TRH) levels to monitor hypothalmic stimulation of the pituitary gland. It is important to consult with an endocrinologist who will conduct the necessary tests and decide upon the most appropriate treatment.
Treatment for Hypothyroidism
Drugs containing synthetic thyroid hormones, like levothyroxine (branded as Eltroxin), are the most common form of treatment. The dosage will be determined by your doctor or endocrinologist and your blood levels will be checked regularly to verify that the drugs are having the desired effect. In cases of other drugs causing low thyroid hormone levels, your doctor may consider stopping the other drug or changing the type of drug.