Hypothyroidism occurs when the thyroid gland produces too little thyroid hormone, when there is decreased conversion from T4 to T3, when there is an overproduction of reverse T3 (Wilson's syndrome), or when the body is not efficiently using thyroid hormone. A large proportion of the population suffers some degree of hypothyroidism; however, the majority of those cases go undiagnosed. Hypothyroidism can occur in either sex at any age, although middle-aged women are most commonly affected. The disease has a wide variety of symptoms, and they often reveal themselves slowly and subtly. Untreated, hypothyroidism can cause anaemia, a low body temperature, heart failure and, ultimately, a condition known as myxoedema coma. This type of coma, triggered by exposure to cold, infection, or drugs such as sedatives, is potentially fatal. It leads to a slowdown in breathing, seizures, and a reduction in the flow of blood to the brain. Hypothyroidism can take several forms, including:

Hashimoto's thyroiditis:
This is the most common type of hypothyroidism. This is an autoimmune response in which antibodies in the blood destroy tissues in the thyroid gland. As a result, the thyroid decreases in size and reduces its production of thyroid hormones.

Post-therapeutic hypothyroidism:
Results from the treatment of hyperthyroidism with radioactive iodine or surgical removal of part or all of the thyroid gland. The treatment can leave the patient's thyroid unable to produce sufficient amounts of thyroid hormone.

Goitrous hypothyroidism:
Results from an extreme shortage of iodine in the diet, producing a goitre in the neck. It is relatively rare in the Western world due to the introduction of iodised salt.

Aetiology / Risk factors:
Major risk factors that can contribute to the incidence of hypothyroidism include:
• Treatment for hyperthyroidism
• Chronic lack of iodine in the diet
• Inherited enzymatic defects
• Chronic stress and adrenal exhaustion
• Toxicity – the thyroid gland is very susceptible to toxins, especially toxic metals
• Positive family and/or personal history of autoimmunity

Signs and Symptoms:
Firm, symmetrical enlargement of the thyroid gland that is not tender on palpation.
Slow pulse
Hoarse voice
Slowed speech
Puffy face
Loss of eyebrows from the sides
Drooping eyelids
Intolerance to cold
Weight gain
Dry, scaly, thick, coarse hair
Raised, thickened skin over the shins
Carpal tunnel syndrome
Menstrual cramps
Increased risk miscarriage
Other menstrual disorders