Hyperthyroidism Flashcards
Control of thyroid activity
Hypothalamus release TRH
Pituitary release TSH
Thyroid produces T3 and T4 - negative feedback to hypothalamus and pituitary
Control of thyroid replacement
Autoimmune destroys thyroid gland
TSH rises
Replace thyroxine and adjust dose until TSH falls
Graves’ Disease
Autoimmune
Antibodies bind to and stimulate the TSH receptor in the thyroid
Cause goitre (smooth) and hyperthyroidism
Other antibodies bind to muscles behind the eye and cause exophthalmos
Other antibodies cause pretibial myxoedema (hypertrophy) - The swelling (non-pitting) that occurs on the shins of patients with Graves’ disease - growth of soft tissue (not myxoedemua - hypothyroidism)
Plummer’s disease
Toxic nodular goitre NOT autoimmune Benign adenoma that is overactive at making thyroxine. NO pretibial myxoedema NO exophthalmos
Effects of thyroxine on the sympathetic nervous system
Sensitises beta adrenoceptors to ambient levels of adrenaline and noradrenaline.
Thus there is apparent sympathetic activation
Tachycardia, palpitations, tremor in hands, lid lag
Hyperthyroidism
Weight loss despite increased appetite Breathlessness, palpitations, tachycardia Sweating Heat intolerance Diarrhoea Lid lag and other sympathetic features
Thyroid storm
Medical emergency : 50% mortality untreated
Blood results confirm hyperthyroidism
Hyperpyrexia > 41oC accelerated tachycardia / arrhythmia cardiac failure delirium / frank psychosis hepatocellular dysfunction; jaundice
Needs aggressive treatment
Treatment options for hyperthyroidism
Surgery (thyroidectomy)
Radioiodine
Drugs
Classes of drugs used in the treatment of hyperthyroidism
- The thionamides (thiourylenes; anti-thyroid drugs)
- propylthiouracil (PTU)
- carbimazole (CBZ) - Potassium Iodide
- Radioiodine
- β-blockers - help symptoms
Thionamide mechanism
inhibition of thyroid peroxidase and hence T3/4 synthesis and secretion
Aim to stop after 18 months
Unwanted actions of thionamides
Agranulocytosis (usually reduction in neutrophils) - rare and reversible on withdrawal of drug.
rashes (relatively common)
Role of b blockers in thyrotoxicosis
Several weeks for ATDs to have clinical effects eg reduced tremor, slower heart rate, less anxiety
NON-selective (ie b1 & b2) b blocker
eg propranolol
achieves these effects in the interim
IODIDE, usually KI
Doses at least 30 times the average daily requirement
preparation of hyperthyroid patients for surgery
severe thyrotoxic crisis (thyroid storm)
KI mechanism
Inhibits iodination of thyroglobulin
Inhibits H2O2 generation + thyoperoxidase
Inhibition of thyroid hormone synthesis & secretion
WOLFF–CHAIKOFF effect - presumed autoregulatory effect
Problem with surgery
Risk of voice change
Risk of also losing parathyroid glands
Scar
Anaesthetic
Radioiodine
Swallow a capsule containing about 370 MBq (10 mCi) of the isotope I (131)
Contraindicated in pregnancy
Need to avoid children and pregnant mums for a few days
For scans only (not treatment), 99-Tc pertechnetate is an option.
Viral (de Quervain’s) thyroiditis
Painful dysphagia
Hyperthyroidism
Pyrexia
Thyroid inflammation
Natural history of viral thyroiditis
Virus attacks thyroid gland causing pain and tenderness
Thyroid stops making thyroxine and makes viruses instead
Thus no iodine uptake (ZERO)
Radioiodine uptake zero
Stored thyroxine released - free T4 level rises
Thus toxic with zero uptake
Four weeks later, stored thyroxine exhausted, so hypothyroid.
After a further month, resolution occurs (like in all viral diseases).
Patient then becomes euthyroid again.
Postpartum thyroiditis similar but no pain and only occurs after pregnancy
