Hyper/hypothyroidism Flashcards
What is the thyroid gland made up of (anterior)?
Pyramidal lobe (sometimes absent)
Right lobe
Isthmus
Left lobe
What is the thyroid gland made up of (posterior)?
Superior parathyroid glands
Inferior parathyroid glands
What is main function of the thyroid gland?
Synthesis thyroid hormones (T3 and T4), thyroxine.
Secretion of calcitonin
Where is the thyroid gland found?
At the base of the neck
What is the functions of parathyroid?
Maintenance of serum calcium and phosphate levels through secretin of parathyroid hormone (PTH)
What effects to T3 and T4 have one the body? (4)
1) Cardiovascular
2) Metabolic
3) Developmental
4) Other
What produces T3 and T4?
Iodine (Mono and Di)
Thyroid hormones mechanism?
- Hypothalamus = TRH
- Pituitary = TSH
- Thyroid = T4 and T3 to go and work peripherally (T2 excreted)
- Then feedback to pituitary and hypothalamus to turn off.
What is ratio of T4 and T3 produced?
10:1 (more T4)
Types of hypothyroidism
Primary
Secondary
Peripheral
What is primary hypothyroidism?
Disfunction in the thyroid itself.
What is secondary hypothyroidism?
Reduced thyroid stimulation (TSH or TRH)
What is peripheral hypothyroidism?
Circulating levels are enough but the body cannot use them
Causes of hypothyroidism (5)
- Autoimmune thyroiditis
- Iodine deficiency
- Post thyroidectomy or radioactive iodine treatment
- Drug induced (lithium)
- Peripheral resistance to thyroid hormone
- Congenital diseases e.g., thyroid agenesis
Diagnosis of hypothyroidism
- Sympotoms
2. Biochemical testing – Thyroid function and TSH and Free T4
Why does a high TSH indicate hypothyroidism?
Because they body if not producing enough thyroxine, so the body is indicating the need for more via TSH
High TSH and normal T4 =
Subclinical hypothyroidism (just about able to manage)
Low TSH and normal T4
Subclinical hyperthyroidism (just about able to manage)
High TSH and low T4 =
Primary hypothyroidism (likely autoimmune thyroiditis)
Low TSH and high T4 =
Primary hyperthyroidism (likely Graves’ disease)
Aim for treatment for hypothyroidism
- Effectivly replace thyroid hormone
2. Correct TSH levels and resolve clinical symptoms
1st line drug for hypothyroidism
Levothyroxine (T4 replacement)
What do you do with people with glucocorticoid deficiency before starting thyroxine?
Glucocorticoid replacement
What is monitored in use of thyroxine?
TFTs every 3 months until stable then annually
How long can it take for TSH to stabiles with use of thyroxine?
6 months. Most adults stabiles at does between 100-200 micrograms. (do not really go over)
In what doses is thyroxine titrated?
25 micrograms
How is thyroxine dose decided?
Based on weight (1.6/kg rounded to nearest 25 microgram)
Why are drug interaction important for thyroxine?
It get absorbed and bounds reduces its use.
Thyroxine main interactions
Calcium and iron should not be taken at the same time as they bind. Also PPIs.
Milk
How may IBD or coeliac impact levothyroxine dose?
May need higher doses due to absorption issues.
How to take levothyroxine?
In the morning 30-60 mins before food.