Thyroid Disorders Flashcards
What is the endocrine system?
A collection of glands that secrete hormones directly into the circulation to be carried to distant organs
What are the endocrine glands?
- Hypothalamus
- Pituitary glands
- Pineal gland
- Thyroid gland
- Parathyroid glands
- Thymus gland
- Adrenal gland
- Pancreas
- Ovary
- Testes
What is the function of the thyroid gland?
Synthesis, storage and secretion of thyroxine (T4) and triiodothyronine (T3)
How does thyroid stimulation work?
- The hypothalamus releases thyrotrophin releasing hormone.
- This then stimulates the anterior pituitary to release thyroid stimulating hormone.
- TSH stimulates the thyroid to produce T3 &T4
If T3 is too high - negative feedback to anterior pituitary to stop releasing TSH
If T4 too high - negative feedback to hypothalamus to stop producing TRH
What do T3 and T4 do?
- Stimulate metabolism - lipid and carbohydrate
- Influence growth and development
- Other effects on CNS, CV and reproductive system
Who is affected most by hypothyroidism?
Women (5-10x more) associated with CV disease
Who is affected by thyrotoxicosis?
CV disease and osteoporosis
How would you investigate thyroid disease?
- Suspect in people with depression or unexplained anxiety
- Measure free T3 and T4 levels only if abnormal TSH
What is hypothyroidism?
Decreased production of thyroid hormones
What does hypothyroidism cause?
Slowing down of body processes due to decreased metabolic function
What is the onset of hypothyroidism?
30-60 years old
What causes primary hypothyroidism?
- Post-operative hypothyroidism
- Anti-thyroid drugs
- Auto-immune hypothyroidism
What causes secondary hypothyroidism?
- Hypopituitarism - deficiency in hormones made
- Hypothalamic disease
What are the signs and symptoms of hypothyroidism?
- Weight gain
- Fatigue
- Constipation
- Depression
- Being sensitive to cold
- Muscle aches and weakness
- Muscle cramps
How do you treat hypothyroidism?
Levothryoxine sodium - maintain TSH levels within ref range but this may take 6 months to achieve
- Starting dose (adults 18-49) - 50 to 100 micrograms daily
- Increase dose by 25-50 micrograms every 3-4 weeks according to response
- Maintenance dose - 100 to 200 micrograms daily
- Starting dose (adults over 50 or cardiac disease) - 25 - 50 micrograms daily
- Preferably taken 30 mins before breakfast or caffeine containing liquids
What is hyperthyroidism?
Excessive production and secretion of thyroid hormone
What does hyperthyroidism cause?
Increased metabolism of all body systems
What causes hyperthyroidism?
- Graves’ disease (toxic diffuse goitre)
- thyroid stimulating antibodies mimic the effects of TSH
- overactivity of the thyroid gland
- inflammation of tissue around the eye
- genetic predisposition
- Toxic nodular goitre
- single hyperfunctioning nodule
What are the signs and symptoms of hyperthyroidism?
- Nervousness, anxiety and irritability
- Mood swings
- Difficulty sleeping
- Persistent tiredness and weakness
- Sensitivity to heat/increased sweating
- Swelling in neck due to enlarged goitre
- Palpitations
How would you treat hyperthyroidism?
- Anti thyroid drugs, initially supplemented by beta blockers
- Radioactive iodine
- Surgery
How do antithyroid drugs work?
They prevent thyroid hormone synthesis
What antithyroid drugs are used to treat hyperthyroidism?
- Carbimazole - initially 15-40 mg daily progressively reduced to a maintenance dose of 5-15 mg daily
- take FBC and LFT before starting
- take for 12-18 months
- Propylthiouracil - initially 200-400 mg daily reduced to a maintenance dose of 50-150 mg daily
- used if there is a sensitivity to carbimazole (2nd line)
- Beta blockers - propranolol 20-40 mg 2 to 4 times daily
- rapid relief of palpitations, anxiety, sweating and tremor
- used adjunct to radioactive iodine and carbimazole in the first few weeks
What is the blocking replacement regimen?
Giving high dose carbimazole (40 - 60mg/day) to block production and levothyroxine (50 - 150 micrograms/day) to supplement for 4 - 6 weeks
What are the S/E’s of carbimazole?
- Neutropenia
- Agranulocytosis
- Recognition of bone marrow suppression
- Patients should report signs and symptoms of infection esp sore throat
- Stop promptly if clinical or lab evidence of neutropenia
Radioactive iodine (131I)…
- Is safe - most patients become hypothyroid
- C/I in children, pregnancy and breastfeeding
- Euthyroidism within 2-3 months
Surgery…
- Patients should be biochemically euthyroid
- Iodine 10-14 days before surgery
- Less frequently used
