Hyperthyroidism Flashcards
What are the 2 effects of TSH on the Thyroid gland?
Activates Iodide uptake
Activates thyroxine release
Briefly summarise control of thyroid activity?
TRH released from Hypothalamus causes TSH to be released from pituitary gland. TSH causes thyroid to release T4(thyroxine) & T3, which act in a negative feedback loop.
What level of TSH will you find in a patient with primary hypothyroidism, where the thyroid gland has been destroyed by the immune system?
High TSH
Lack of T4 will cause increase in TSH, slowly increase dose of thyroxine until you have a normal TSH.
What is Graves Disease?
Autoimmune disease whereby antibodies bind to and stimulate the TSH receptor in the thyroid gland, more and more T4 produced. Thyroid gland gets bigger (smooth goitre), and you get hyperthyroidism.
What are the symptoms of hyperthyroidism?
Unintentional weight loss, even when your appetite and food intake stay the same or increase.
Rapid heartbeat (tachycardia) — commonly more than 100 beats a minute.
Irregular heartbeat (arrhythmia)
Pounding of your heart (palpitations)
Increased appetite.
Nervousness, anxiety and irritability.
What do the other antibodies in Graves disease cause?
Other antibodies bind to muscles behind the eye and cause exophthalmos
Other antibodies cause pretibial myxoedema (hypertrophy)
What is pretibial myxcoedema?
The swelling (non-pitting) that occurs on the shins of patients with Graves’ disease, do not confuse myxoedema-hypothyroidism.
What would you see in a radio-iodine uptake scan in a person with Graves disease?
Diffuse enlargement and engorgement of thyroid gland (broken line indicates normal size of gland).
Diffuse goitre of moderate size and uniform radioiodine uptake.
What is Toxic nodular goitre (Plummer’s disease)?
Benign adenoma that is overactive at making thyroxine.
Not autoimmune
No pretibial myxoedema
No exophtalmos
One side will be much larger than the other. lump on one side. Nodular goitre.
What is the effect of thyroxine on the sympathetic nervous system?
Sensitises beta adrenoreceptors to ambient levels of adrenaline and noradrenaline. you still have normal levels the receptors are just more sensitive. So there is only apparent sympathetic activation.
What happens due to the increased beta adrenoreceptors sensitivity?
Tachycardia, palpitations, tremor in hands, lid lag
What happens in thyroid storm?
Person with hyperthyroidism with 2 or more of these features; Hyperpyrexia > 41oC accelerated tachycardia / arrhythmia cardiac failure delirium / frank psychosis hepatocellular dysfunction; jaundice Needs aggressive management 50% mortality untreated
What are the treament options for hyperthyroidism?
Surgery (thyroidectomy)
Radioiodine
Drugs
What are the 4 classes of drugs used in the treatment of hyperthyroidism?
- The thionamides (thiourylenes; anti-thyroid drugs)
- propylthiouracil (PTU)
- carbimazole (CBZ) - Potassium Iodide
- Radioiodine
- β-blockers
The first 3 drugs reduce thyroid hormone synthesis, beta blockers help with symptoms.
How do thionamides work?
Inhibit thyroid peroxidase enzyme & hence T4 &T3 enzyme synthesis, takes 4-6 weeks for thyroxine levels to go down due to stored thyroxine. So you need to give a beta blocker (propranolol) as well, for immediate effect.
