Hypothyroidism Flashcards
What is hypothyroidism?
Hypothyroidism is a common endocrine condition caused by a deficiency in thyroid hormone.
Reduction in circulating T3 and T4
What are the classification for hypothyroidism?
Primary - 95% of cases
Secondary
Congenital
Epidemiology
- Hypothyroidism 1-2% in world
- Hashimoto’s thyroiditis being the most common cause in the developed world. Iodine deficiency is the most common cause worldwide.
- Female gender: 5-8x more likely to develop than men
- Middle-aged: peak age is 30-50 years old in Hashimoto’s thyroiditis
Hashimotos thyroiditis
- Autoimmune process associated withHLA-DR5andanti-TPO antibodies,which act as competitive inhibitors for the enzyme
- Associated with other autoimmune conditions e.g. type 1 diabetes and Addisons disease
- Diffuse painless goitre and can experience a transient thyrotoxic state known as hashitoxicosis
- 5-10x more common in women
- Increased risk of Non-Hodgkin lymphoma
De Quervain’s thyroiditis
- Follows a viral prodrome and can also present with a transient thyrotoxic state
- Painfulgoitre withraised inflammatory markers. Usually self-limiting
Post partum thyroiditis
- Autoimmune with most patients developingthyrotoxicosiswithin the first 6 months of birth, with subsequenthypothyroidism
- Most patients’ thyroid function normalises by 12 months
Riedels thyroiditis
- Hard non-tender thyroid goitre due to fibrous tissue
- Causes a painless goitre
Iodine deficiency
- Commonest causeworldwide, due to dietary deficiency
- Uncommon in the developed world due to iodine-fortified salt and foods
Post- thyroidectomy or post radioiodine
After treatment for hyperthyroidism e.g. Graves’ disease, patients can experience long term hypothyroidism and require levothyroxine replacement
Drugs that cause primary hypothyroidism
- Amiodarone - can cause both hyperthyroidism (due to the high iodine content of amiodarone) and hypothyroidism (since it also inhibits the conversion of T4 to T3)
- Lithium
- Anti-thyroid drugs e.g. carbimazole
Secondary causes of hypothyroidism
- Often due to compression from apituitarytumour(e.g. adenoma), but may occur following surgery/radiation or vascular pathology (e.g. pituitary apoplexy)
- Rarely, it may be due tohypothalamicpathology, e.g. a tumour
- Drugs: cocaine, steroids and dopamine all inhibit TSH secretion
What is primary hypothyroidism?
due to pathology affecting the thyroid gland itself, such as an autoimmune disorder (e.g. Hashimoto’s thyroiditis) or iodine deficiency.
What is Secondary hypothyroidism?
usually due to pathology affecting thepituitarygland (e.g. pituitary apoplexy) or a tumour compressing the pituitary gland. It may also be caused byhypothalamicdisorders and certain drugs.
What is congenital hypothyroidism?
occurs due to an absent or poorly developed thyroid gland (dysgenesis), or one that has properly developed but cannot produce thyroid hormone (dyshormonogenesis).
RFs for hypothyroidism
- Family history
- History of autoimmunity
- Genetic disorders: Turner and Down syndrome
- Chest or neck irradiation
- Thyroidectomy or radioiodine