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Hypothyroidism occurs when the body does not have sufficient effect of the biologically active T3 within the tissues of the body.
It can happen through low levels of thyroid hormones, poor conversion from T4 to T3, low levels of other co-factors like cortisol or ferritin etc., and many other more complicated processes that are not working well any more.
Some of the main symptoms associated with hypothyroidism include:
- Feeling cold.
- Low body temperature.
- Reduced sweating.
- Myxoedema (swollen skin especially on the face, eyelids, upper arms and hands).
- Weak muscles.
- Muscular cramps or pain.
- Joint pain.
- Slow movement.
- Thin, brittle, cracked fingernails.
- Coarse hair.
- Hair loss.
- Dry, coarse, itchy skin.
- Acne and skin infections.
- Pale skin.
- Weight gain.
- Water retention.
- Low heart rate (lower than sixty beats per minute).
- Heart palpitations.
- Changes in voice (slower, rougher).
- Swollen tongue.
- Abnormal or painful menstrual cycles.
- Poor memory.
- Impaired thinking ability (brain fog).
- Lack of concentration.
- Sluggish reflexes.
- Swallowing problems.
- Loss of appetite.
- Shortness of breath, laboured breathing.
- Need for more sleep than normal.
- Decreased libido.
- Irritability, mood swings.
Myxoedema is common in severely hypothyroid patients and it is caused by mucin, which is a glue-like substance that fills parts of the skin. If myxoedema is present then it is often difficult to slightly lift up areas of the skin, using the thumb and forefinger. The presence of this particular clinical feature, combined with a low body temperature and any of the other more common symptoms listed above, used to be the main method of diagnosing hypothyroidism prior to the advent of thyroid blood tests.
Primary hypothyroidism, where the thyroid gland fails to produce enough T4 and T3, is the most common type of hypothyroidism and the patient is therefore said to have an under-active thyroid.
Secondary hypothyroidism is less common and occurs if the pituitary gland itself fails to produce enough TSH. This condition is called secondary hypothyroidism.
Tertiary hypothyroidism is due to a fault within the hypothalamus gland.
Secondary and tertiary hypothyroidism may be collectively referred to as central hypothyroidism.
However, these medical definitions do not cover some of the more common issues like poor conversion of T4 to T3, or lower co-factors like ferrritin (storage iron) or hypocortisolism.