Hypothyroidism Flashcards
What is hypothyroidism?
Hypothyroidism refers to insufficient thyroid hormones, triiodothyronine (T3) and thyroxine (T4).
What is primary hypothyroidism?
Primary hypothyroidism occurs when the thyroid gland behaves abnormally, producing insufficient thyroid hormones. Negative feedback is absent, leading to increased production of TSH. TSH is high, and T3 and T4 are low.
What is secondary hypothyroidism?
Secondary hypothyroidism (central hypothyroidism) occurs when the pituitary gland produces insufficient TSH, resulting in under-stimulation of the thyroid and low TSH, T3, and T4.
What are the TSH, T3, and T4 levels in primary hypothyroidism?
In primary hypothyroidism, TSH is high, and T3 and T4 are low.
What are the TSH, T3, and T4 levels in secondary hypothyroidism?
In secondary hypothyroidism, TSH is low, and T3 and T4 are low.
What is the most common cause of primary hypothyroidism in the developed world?
The most common cause of primary hypothyroidism in the developed world is Hashimoto’s thyroiditis, an autoimmune condition causing thyroid inflammation.
What antibodies are associated with Hashimoto’s thyroiditis?
Hashimoto’s thyroiditis is associated with anti-thyroid peroxidase (anti-TPO) antibodies and anti-thyroglobulin (anti-Tg) antibodies.
What is the most common cause of hypothyroidism in the developing world?
The most common cause of hypothyroidism in the developing world is iodine deficiency.
What treatments for hyperthyroidism can cause hypothyroidism?
Treatments for hyperthyroidism that can cause hypothyroidism include:
* Carbimazole
* Propylthiouracil
* Radioactive iodine
* Thyroid surgery
How does lithium affect thyroid function?
Lithium inhibits the production of thyroid hormones in the thyroid gland, potentially causing goitre and hypothyroidism.
How does amiodarone affect thyroid function?
Amiodarone can interfere with thyroid hormone production and metabolism, usually causing hypothyroidism but can also cause thyrotoxicosis.
What are the causes of secondary hypothyroidism?
Secondary hypothyroidism is often caused by:
* Pituitary tumours (e.g., pituitary adenomas)
* Pituitary surgery
* Radiotherapy
* Sheehan’s syndrome (postpartum haemorrhage leading to pituitary necrosis)
* Trauma
What are the universal features of hypothyroidism?
Universal features include:
* Weight gain
* Fatigue
* Dry skin
* Coarse hair and hair loss
* Fluid retention (oedema, pleural effusions, ascites)
* Heavy or irregular periods
* Constipation
What does iodine deficiency cause in hypothyroidism?
Iodine deficiency causes a goitre (swelling of the thyroid gland).
What happens to the thyroid gland in Hashimoto’s thyroiditis over time?
In Hashimoto’s thyroiditis, there is an initial goitre, followed by atrophy (wasting) of the thyroid gland.
What is the main treatment for hypothyroidism?
The main treatment for hypothyroidism is oral levothyroxine, a synthetic version of T4 that metabolizes to T3 in the body.
How is the dose of levothyroxine adjusted?
The levothyroxine dose is titrated based on TSH levels, typically checked every 4 weeks:
* High TSH: Increase the dose
* Low TSH: Decrease the dose
What is liothyronine sodium, and when is it used?
Liothyronine sodium is a synthetic version of T3 and is rarely used under specialist care when levothyroxine is not tolerated.
