Hypothyroidism Flashcards
What is hypothyroidism?
Inadequate production of thyroid hormone.
Outline thyroid hormone synthesis.
- Tyrosine have 1 or 2 Iodides (iodination)
- Two tyrosines bind on the surface of a thyroglobulin (coupling)
- T3 and T4 made
What enzyme drives thyroid hormone production?
Thyroid peroxidase
What is the most common cause of hypothyroidism?
Hashimoto’s Thyroiditis
What are the other causes of hypothyroidism?
MISS
- Medications
- Iodine deficiency
- Secondary to Tx of hyperthyroidism
- Secondary Hypothyroidism
What medications cause hypothyroidism?
Lithium- inhibits thyroid hormone production
Amiodarone- interferes with thyroid hormone metabolism, can cause either hyper or hypothyroidism
How is iodine deficiency prevented in the western world?
Iodised salts etc.
What is a secondary hypothyroidism?
Hypothyroidism caused by pituitary failure.
Which pituitary gland releases TSH?
Anterior pituitary
What can cause hypopituitarism? (Pituitary failure)
- Tumour
- Infection
- Vascular e.g. Sheehan syndrome
- Radiation
How does hypothyroidism present?
- Weight gain
- Fatigue
- Dry skin
- Hair loss
- Fluid retention
- Constipation
- Amenorrhoea
What would TFTs show for primary hypothyroidism?
Low T3/4
High TSH
What would TFTs show for secondary hypothyroidism?
Low T3/4
Low TSH
How is hypothyroidism treated?
Levothyroxine
What is levothyroxine?
Synthetic T4
What happens to levothyroxine after it is absorbed?
Converted to T3
How is treatment optimised?
Dose titration- use TSH as a marker
What should you do if TSH is low on levothyroxine?
Lower the dose
What should you do if TSH is high on levothyroxine?
Increase the dose
What are the complications of hypothyroidism?
- CARDIOVASCULAR- Low T3/4 increases cholesterol, causing CVD
- Pregnancy complications
