Hypothyroidism

• Hypothyroidism can be stratified into primary and secondary causes:

  • Primary hypothyroidism refers to thyroid hormone underproduction caused by the thyroid gland itself
  • Secondary hypothyroidism refers to thyroid hormone underproduction caused by the structures/factors external to the thyroid gland
• Hashimoto's disease is the most common cause of hypothyroidism in western populations. Anti-thyroid peroxidase antibodies (Anti-TPO) attack the thyroid gland. It is 4 times more common in women, and usually in 30-50 year olds. Individuals with other autoimmune conditions such as diabetes and rheumatoid arthritis are more likely to develop Hashimoto's disease
• Iodine deficiency is the most common cause of hypothyroidism worldwide. Iodine is a key component of thyroxine (T4) and triiodothyronine (T3). Therefore, a deficiency leads to the underproduction of thyroid hormones.
• Congenital hypothyroidism is a condition present from birth where the thyroid gland is underdeveloped or absent, resulting in thyroid hormone deficiency. Symptoms include reduced tone, poor growth, and if untreated, can lead to developmental delay
• Pituitary tumours such as pituitary adenomas can cause central hypothyroidism by compressing the pituitary gland or interrupting the gland’s blood flow, which can reduce the production of TSH. This can subsequently lead to secondary hypothyroidism due to a lack of stimulation to produce the thyroid hormones.
• De Quervain’s thyroiditis is a transient inflammation of the thyroid gland causing three stages: thyrotoxicosis, hypothyroidism and euthyroidism. It is usually triggered by a virus and is a self-limiting condition. Presents with a painful and swollen lump.
• Following the relative immunosuppressive state of pregnancy, thyroid gland inflammation can occur post-partum. Classically, this is triphasic: hyperthyroidism, hypothyroidism and euthyroidism. However, the hypothyroid period of this condition may persist in 20-30% of cases
• Iatrogenic causes such as medications, sphenoid surgery and radiotherapy to the brain may also cause hypothyroidism. Medications that commonly cause hypothyroidism include amiodarone and lithium.
• Risk factors for hypothyroidism include:

  • A family history of hypothyroidism
  • Pregnancy in the last six months
  • Autoimmune diseases such as type 1 or 2 diabetes, coeliac disease and rheumatoid arthritis
  • Previous thyroid surgery or treatment with radioactive iodine
  • Radiation treatment to the head, neck or thorax
• Typical symptoms of hypothyroidism include:

  • Weight gain
  • Constipation
  • Depression
  • Brittle hair and nails
  • Irregular or heavy periods
  • Loss of libido
  • Lethargy
  • Cold intolerance
• Typical clinical findings of hypothyroidism on examination may include:1

  • Dry skin
  • Bradycardia
  • Cold peripheries
  • Stiff muscles
  • Hair loss
• A rare sign of hypothyroidism of Hertoghe's sign - loss of the outer third of the eyebrow
• TFTs in primary hypothyroidism:

  • Raised TSH
  • Low T3 and T4
• TFTs in secondary hypothyroidism:

  • Low or normal TSH - reduced pituitary production
  • Low T3 and T4
• Testing for autoantibodies such as anti-thyroid peroxidase (anti-TPO) can aid the identification of autoimmune thyroid conditions. TPO antibodies are found in 90% of people with Hashimoto’s thyroiditis. However, they may also be present in Grave’s disease
• Patients with hypothyroidism where a secondary cause or malignancy is suspected, they should be referred for specialist assessment including an ultrasound
• 1st line treatment of hypothyroidism is monotherapy with levothyroxine and review TFTs every 8-12 weeks

  Levothyroxine takes 4-8 weeks to take affect so will have to wait at least 4 weeks after starting levothyroxine to assess if working
• Myxoedema coma is a rare and potentially fatal complication of hypothyroidism:

  • Altered mental state
  • Hypothermia
  • Bradycardia
  • Hypoventilation
  • Treatment is with thyroid replacement therapy, glucocorticoid therapy and supportive measures
• Cardiac complications of hypothyroidism:

  • Raised total and LDL cholesterol
  • Risk of coronary artery disease, heart failure and atherosclerosis
• Hypothyroidism can impact on the female reproductive system:

  • Sub-fertility
  • Increased risk of miscarriage, stillbirth, pre-eclampsia and postpartum haemorrhage
• Liothyronine is a treatment of hypothyroidism for people that are unable to convert T4 to T3 peripherally

  It is a T3 replacement