Endocrinology - Hypothyroidism Flashcards
Causes of hypothyroidism
Hashimoto’s thyroiditis
Iodine deficiency (rare in UK)
Secondary to treatment of hyperthyroidism
Medications e.g. lithium and amiodarone
Secondary hypothyroidism - hypopituitarism
Hashimoto’s thyroiditis cause
Autoimmune inflammation of thyroid gland
Associated with antithyroid peroxidase (anti-TPO) antibodies and antithyroglobulin antibodies
Most common cause in the UK
Iodine deficiency as a cause
Most common cause of hypothyroidism in developing countries
Rare in UK as iodine added to foods such as salt to prevent this
What medications/procedures can cause hypothyroidism?
Those used to treat hyperthyroidism:
- Carbimazole and PTU
- Radioactive iodine
- Thyroid surgery
Lithium - inhibits the production of thyroid hormones in the thyroid gland (can cause goitre and hypothyroidism)
Amiodarone - interferes with thyroid hormone production and metabolism (usually causes hypo but can also cause hyperthyroid)
Causes of secondary hypothyroidism
Tumours
Infection
Vascular (e.g. Sheehan Syndrome)
Radiation
Presentation of hypothyroidism
Weight gain Fatigue Dry skin Coarse hair and hair loss Fluid retention (oedema, pleural effusions, ascites) Heavy or irregular periods Constipation
Investigations in hypothyroid
TFTs - TSH and T3/4
High TSH and low T3/4
Primary hypothyroidism - most likely Hashimoto’s thyroiditis
Low TSH and low T3/4
Secondary hypothyroidism (hypopituitarism)
Management of hypothyroidism
Levothyroxine (synthetic T4 - which metabolises to T3 in the body)
Dose is titrated until TSH levels are normal
Initially TSH measured monthly but less frequently once stable.
- If TSH is high - need to increase dose
- If TSH low - need to reduce dose
Initially 1.6 micrograms/kg once daily to nearest 25 micrograms
Dose taken before breakfast
