Thyroid Disorders Flashcards
What is the physiology of thyroid function hormones?
The hypothalamus releases TRH which travels to the anterior pituitary = TSH is produced by the anterior pituitary and travels to the thyroid gland to produce T4. T3 is produced by the peripheral conversion of T4 to T3 and T3 is more active.
T3 and T4 travel in the blood bound to thyroxine-binding globulin.
T3 and T4 increase cell metabolism and increase Catecholamine effects,
What is the difference between the serum levels of free T3 and T4 and total T3 and T4?
Total T3 and T4 is bound to TBG, and thus is increased when TBG is increased.
Free T3 and T4 is a more accurate representation.
What conditions can increase TBG?
Pregnancy
Oestrogen therapy (HRT, COCP)
Hepatitis
What conditions can decrease TBG?
Nephrotic syndrome and malnutrition (due to protein loss)
Drugs (androgens, corticosteroids, phenytoin)
Chronic liver disease
Acromegaly
What is the general presentation of TFTs in hyperthyroidism?
Decreased TSH
Raised T4
What is the general presentation of TFTs in hypothyroidism?
TSH varies throughout the day (trough at 2pm)
What patients must have their TFTs screened?
AF Hyperlipidaemia Diabetes mellitus Patients on amiodarone or lithium Downs, Turners, Addisons
What hormone profile will you see in hypothyroidism?
Increased TSH
Decreased T4
What hormone profile will you see in a patient with treated hypothyroidism or sub clinical hypothyroidism?
Raised TSH
Normal T4
What hormone profile will you see in patients with a TSH secreting tumour or thyroid hormone resistance?
Raised TSH
Raised T4
What hormone profile will you see in a patient with hyperthyroidism?
Decreased TSH
Increased T4 or T3
What hormone profile will you see in a patient with sub clinical hyperthyroidism?
Low TSH
Normal T3 and T4
What hormone profile will you expect to see in a patient with sick euthyroidism or pituitary disease?
Decreased TSH
Decreased T4 and T3
What are the signs of hypothyroidism?
BRADYCARDIC Reflexes slow Ataxia (cerebellar) Dry thin hair/skin Yawning/drowsy/coma Cold hands and decreased temperature Ascites and non pitting oedema Round puffy face/double chin Defeated demeanour Immobile CCF
How do you diagnose hypothyroidism?
Increased TSH
Decreased T4
Increased cholesterol and triglycerides
Macrocytosis
What are the causes of primary autoimmune hypothyroidism?
Primary atrophied hypothyroidism (lymphocytic infiltration of thyroid leading to atrophy, hence no goitre)
Hashimoto’s thyroiditis (goitre due to lymphocytic infiltration. Older women.
What are the causes of primary hypothyroidism?
Iodine deficiency (1) Post thyroidectomy Drug induced (anti thyroid drugs, amiodarone, lithium, iodine)
What is secondary hypothyroidism?
Not enough TSH (due to hypopituitarism)
What is the treatment of primary hypothyroidism?
Healthy and young: levothyroxine 0-100mcg/24h. Review at 12 weeks
Elderly or IHD: levothyroxine 25mcg/24h, increase by 24mcg/4weeks according to TSH
If someone has already been given levothyroxine and the diagnosis of hypothyroidism is being debated, what should you do?
Stop levothyroxine
Recheck TSH in 6 weeks
How can amiodarone cause thyroid problems?
Amiodarone is iron rich and structurally like T4. Some patients on amiodarone may begin to have their T4 release inhibited, resulting in hypothyroidism
When should you suspect sub clinical hypothyroidism?
When should you treat it?
Suspect if TSH >4 with normal T3 and T4.
Treat if TSH >10 Positive thyroid autoantibodies Past Graves' disease Other organ specific autoimmunity
What are the symptoms of thyrotoxicosis?
Tremor Sweating Weight loss Tachycardia Exaggerated reflexes Palpitations Oligomenorrhoea and infertility Chorea Itch Urticaria
What are the signs of thyrotoxicosis?
Irregular or fast pulse Warm moist hands Fine tremor Palmar erythema Lid lag Goitre or thyroid nodules may be present
What are the specific symptoms of Graves’ disease?
1) Exophthlamos/ophthalmoplegia
2) Pretibial myxoedema
What do tests show in thyrotoxicosis?
Decreased TSH (suppressed), T4 and increased T3 Increased ESR, calcium, and LFTs Check thyroid autoantibodies
What are the causes of thyrotoxicosis?
Graves' disease Toxic multinodular goitre Toxic Adenoma Ectopic thyroid tissue Exogenous
What happens in Graves’ disease?
Typical in 40-60 year olds and caused by circulating IgG autoantibodies that bind to and activate thyrotopin receptors, which cause thyroid enlargement and increased hormone production.
Stress, infection, and childbirth can trigger it.
What happens in toxic multinodular goitre?
What happens in toxic Adenoma?
Seen in the elderly
Nodules in the thyroid that secrete thyroid hormones
Toxic Adenoma: Singular nodule producing T3 and T4, looks hot on isotope scan
What medications can you use to treat thyrotoxicosis?
Beta blockers: propranolol 40mg/6h for rapid control of symptoms
Anti thyroid medications:
Regimen 1: Carbimazole for 4wks, reduce according to TFTs every 1-2m.
Regimen 2: Carbimazole and levothyroxine simultaneously
In Graves, maintain either regimen for 12 months then withdraw
What is the main SE of carbimazole?
Agranulocytosis
Apart from drugs, what are the other treatments of thyrotoxicosis?
Radio iodine (most become hypothyroid post treatment. CI are pregnancy and lactation) Thyroidectomy
