Hypothyroidism, or underactive thyroid, develops when the thyroid gland fails to produce or secrete as much thyroxine (T4)as the body needs. Because T4 regulates such essential functions as heart rate, digestion, physical growth, and mentaldevelopment, an insufficient supply of this hormone can slow life-sustaining processes, damage organs and tissues inevery part of the body, and lead to life-threatening complications.
The most common cause of hypothyroidism is Hashimoto’s thyroiditis. “Thyroiditis” is an inflammation of the thyroid gland. Hashimoto’s thyroiditis is an autoimmune disorder. With Hashimoto’s, your body produces antibodies that attack and destroy the thyroid gland. Thyroiditis may also be caused by a viral infection.
Hypothyroidism is defined as the deficient production of thyroid hormones from the thyroid gland. Hypothyroidism is broadly classified as a primary, secondary, or tertiary disease depending on the underlying cause. In primary disease there is impaired hormone release from the thyroid gland; in secondary disease, there is defective TSH signaling from the pituitary; in tertiary or central disease, the hypothalamus fails to stimulate thyroid hormone release.Hypothyroidism ranges in severity from subclinical disease, where patients may be asymptomatic, to full blown clinical disease, where patients are severely affected in the presence of multiple laboratory abnormalities.
Because of the range of symptom severity and the relatively common and non-specific nature of clinical findings, diagnosis of hypothyroidism is highly dependent on laboratory testing. The frontline laboratory test for hypothyroidism is thyroid-stimulating hormone (TSH). TSH is elevated in primary hypothyroidism as the pituitary responds to the relative lack of circulating T3 and T4; TSH is abnormal in all clinical and subclinical cases of primary hypothyroidism. As the disease progresses toward clinical or overt hypothyroidism, T4 and T3 become measurably decreased. In secondary and tertiary hypothyroidism, TSH, T4, and T3 levels are variably abnormal depending on the duration, cause, and severity of disease. As a result of the complexity of hypothyroid etiology, laboratory testing for hypothyroidism is complex and beyond the scope of this review.
Below are major symptoms associated with hypothyroidism.
- Weight gain or difficulty losing weight (despite reduced food intake)
- Coarse, dry hair and dry skin
- Hair loss
- Sensitivity to cold
- Muscle cramps and aches
- Memory loss
- Abnormal menstrual cycles
- Decreased libido
- Slowed speech (severe cases)
- Jaundice (severe cases)
- Increase in tongue size (severe cases)
You don’t have to encounter every one of these symptoms to be diagnosed with hypothyroidism. Every patient’s experience with the disorder is different. While you may notice that your skin and hair have become dry and rough, another patient may be plagued more by fatigue and depression.
The thyroid stimulating hormone (TSH) level reflects the severity of the hypothyroidism. For example, if you have a mild form of hypothyroidism and a relatively lower TSH level, you may not notice—or even have—symptoms. That’s because your hormone levels haven’t decreased to the point where they have a major impact on your metabolism. The more hypothyroid you become, the more symptomatic you’ll be.
The symptoms of hypothyroidism aren’t always noticeable, but it’s important that you understand what to look out for. Recognizing hypothyroidism early on will allow you to manage the disorder and prevent it from interfering with your life.
It’s very important that an underactive thyroid (hypothyroidism) is diagnosed as soon as possible.
Low levels of thyroid-producing hormones, such as triiodothyronine (T3) and thyroxine (T4), can change the way the body processes fat.
This can cause high cholesterol and atherosclerosis (clogging of the arteries), which can potentially lead to serious heart-related problems, such as angina and heart attack.
A common treatment is to replace thyroxine with a specific synthetic thyroid hormone (levothyroxine). This hormone is safe and affordable, but determining the right dosage often takes time. Your metabolic rate has to be returned to normal. Raising it too quickly can cause palpitations and make some medical problems like coronary artery disease and atrial fibrillation worse. Symptoms of thyroid hormone excess are:
- shakiness or tremors
- increased appetite
Diets rich in soy and high fiber can interfere with levothyroxine absorption. Medications and supplements also can reduce absorption. These include:
- calcium supplements
- iron supplements
- aluminum hydroxide (present in some antacids)