Hypothyroidism

• Hypothyroidism


  Refers to insufficient thyroid hormones, triiodothyronine (T3) and thyroxine (T4)
• Primary hypothyroidism


  Thyroid behaves abnormally and produces inadequate thyroid hormones, resulting in increased production of TSH, with TSH raised and T3 and T4 low
• Negative feedback


  Absent in primary hypothyroidism, resulting in increased production of TSH
• Secondary hypothyroidism


  Pituitary behaves abnormally and produces inadequate TSH, resulting in under-stimulation of the thyroid gland and insufficient thyroid hormones, with TSH, T3, and T4 all low
• Site of Pathology


  • TSH
  • T3 and T4
• Causes of Primary Hypothyroidism

  • Hashimoto’s thyroiditis
  • Iodine deficiency
  • Treatments for hyperthyroidism
• Hashimoto’s thyroiditis is the most common cause of hypothyroidism in the developed world, an autoimmune condition causing inflammation of the thyroid gland, associated with anti-thyroid peroxidase (anti-TPO) antibodies and anti-thyroglobulin (anti-Tg) antibodies
• Iodine deficiency is the most common cause of hypothyroidism in the developing world, with iodine particularly found in dairy products and may be added to non-dairy milk alternatives (e.g., soya milk)
• Treatments for hyperthyroidism have the potential to cause hypothyroidism, including Carbimazole, Propylthiouracil, Radioactive iodine, Thyroid surgery, and Lithium
• Lithium inhibits the production of thyroid hormones in the thyroid gland and can cause a goitre and hypothyroidism
• Amiodarone interferes with thyroid hormone production and metabolism, usually causing hypothyroidism
• Medications that inhibit the production of thyroid hormones

  • Carbimazole
  • Propylthiouracil
  • Radioactive iodine
  • Thyroid surgery
  • Lithium
• Lithium


  Inhibits the production of thyroid hormones in the thyroid gland and can cause a goitre and hypothyroidism
• Amiodarone


  Interferes with thyroid hormone production and metabolism, usually causing hypothyroidism but can also cause thyrotoxicosis
• Features universal to all causes of hypothyroidism

  • Weight gain, Fatigue, Dry skin, Coarse hair and hair loss, Fluid retention (including oedema, pleural effusions and ascites), Heavy or irregular periods, Constipation
• Iodine deficiency causes a goitre
• Hashimoto’s thyroiditis can initially cause a goitre, after which there is atrophy (wasting) of the thyroid gland
• Management of hypothyroidism


  Oral levothyroxine is the mainstay of treatment. Levothyroxine is a synthetic version of T4 and metabolises to T3 in the body. The dose is titrated based on the TSH level, initially every 4 weeks
• TSH Result and Levothyroxine Dose

  • High TSH - Too low dose, Increase the dose; Low TSH - Too high dose, Reduce the dose
• Liothyronine sodium


  A synthetic version of T3 and is very rarely used under specialist care where levothyroxine is not tolerated