Thyroid, pituitary and adrenal Flashcards
(41 cards)
What does the thyroid do?
→ Secretes thyroxine (T4) and triiodothyronine (T3) stimulated by TSH from the pituitary gland
→ Thyroid hormone production is regulated by hypothalamic thyrotropin-releasing hormone (TRH) which stimulates pituitary thyrotropin (TSH)
→ Protein thyroglobulin (Tg) is used by thyroid to produce T3 and T4
→ T3 is the active form. T4 is the prohormone to T3
→ Thyroid gland produces 100% of T4 but only 20% of T3 (80% in produced by conversion of T4 to T3 in peripheral tissues)
What are the thyroid hormone binding proteins?
→ Thyroxine binding globulin (TBG), pre-albumin (transthyretin) and albumin
→ Most of T4 and T3 are protein bound
The unbound free T3 and T4 (FT3 and FT4) are active
What is the Wolff-Chaikoff effect?
Wolff-Chaikoff effect is an autoregulatory phenomenon, whereby a large amount of ingested iodine acutely inhibits thyroid hormone synthesis within the follicular cells, irrespective of the serum level of thyroid-stimulating hormone (TSH)
What are the symptoms of hypothyroidism?
Weakness Lethargy Weight gain Depression Feeling cold Hoarse voice Menorrhagia Hair loss Bradycardia (rare) Goitre Erythema ab igne (hot water bottle rash, is a skin condition caused by long-term exposure to heat because these patients feel cold)
What are the symptoms of hyperthyroidism?
Hyperactivity Irritability Heat intolerance Insomnia Palpitation Dyspnoea Diarrhoea Weight loss Increased appetite Polyuria Polydipsia Pruritus Amenorrhoea Loss of libido
What is the treatment of hyperthyroidism?
Carbimazole
· Decreases uptake of inorganic iodine, reducing formation of T3 and T4
· Can convert into methimazole and present thyroid peroxidase enzyme from coupling and iodinating tyrosine residues on thyroglobulin
Propylthiouracil
· Choice of medication in pregnant and lactating women
· Binds to thyroid peroxidase to inhibit iodide to iodine conversion
· Also inhibits T4 to converting into T3
· Preferred in pregnancy due to the lower concentration found in breast milk
Beta blockers: (80mg BD)
· Symptomatic control of anxiety, palpitations and tremor. Also influences monodeiodinaiton
· Propranolol
Radioiodine therapy:
· Radioactive iodine-131 given orally
· Iodine taken up by thyroid glad for use in thyroid hormone synthesis but the radiation emitted destroys over acting thyroid cells
Thyroidectomy:
Total is preferred over partial thyroidectomy due to risk of relapse
Common side effects of the medications used for hyperthyroidism
Carbimazole: arthralgia, agranulocytosis, headache, jaundice, malaise, pruritus, taste disturbances, aplasia cutis (congenital disorder)
Propylthiouracil: arthralgia, jaundice, leukopenia, malaise, pruritus, taste disturbances
Beta blockers: SOB and drowsiness
Common side effects of radioiodine therapy and thyroidectomy
Radioiodine therapy: normal functioning follicular cells may be destroyed so thyroxine treatment needed after
Thyroidectomy: recurrent laryngeal nerve damage and vocal cord paralysis, hypoparathyroidism, thyroid crisis and local haemorrhage. Long term - formation of keloid scar
What are the symptoms of Addison’s disease?
→ Weight loss and anorexia
→ Hyperpigmentation - increased ACTH leads to melanocyte stimulating hormone production
→ Tiredness and weakness
→ Postural hypotension and dizziness
→ Symptomatic hypoglycaemia
→ Hair loss and reduced libido
→ Salt craving - hyponatraemia due to decreased aldosterone production
What are the symptoms of cushing’s disease?
entral obesity - buffalo hump, moon face, hirsutism, thinning of hair
→ Hypertension (increased release of aldosterone)
→ Diabetes
→ Weakness of muscles
→ Bruising, scarring, purple striae around abdomen - cortisol inhibits fibroblast proliferation and formation of collagen
→ Thinning of skin and loss of connective tissue to support capillaries - more susceptible to injury
→ Decreases new bone formation (decreases osteoblast function)
→ Inhibition of GRH so ovarian and testicular function is impaired
→ Mood disturbances: labile, depression, insomnia, psychosis
Menstrual changes
What are the investigations done for Addison’s?
- U&Es: hyperkalaemia due to reduced aldosterone production. Hyponatraemia as hyperkalaemia increases action of Na+/K+ pump
- Serum cortisol and ACTH
- ACTH syncacthen stimulation test
- Serum glucose - hypoglycaemia
- TFTs - cortisol inhibits TRH
- 24 hour urinary free cortisol
- Dexamethasone suppression test
- Adrenal CT
- FBC - normocytic normochromic anaemia, raised ESR and eosinophilia
- Prolactin testing
What are the causes for hypothyroidism?
Hashimoto’s disease (commonest in developed countries)
Iodine deficiency (commonest in underdeveloped countries)
Drugs (lithium, Amiodarone, Iodine)
Thyroidectomy/radio-iodine therapy
Haemochromotosis
What are the causes of hyperthyroidism?
Graves' disease (TRAb) Drugs (Amiodarone, oestrogen) Toxic nodular goitre Thyroiditis TSH secreting tumours
What is the treatment for hypothyroidism?
Levothyroxine (1.6 microgram/kg)
Lower dose given to patients with history of ishaemic heart disease
Overtreating can lead to osteoporosis and arrhythmias
What are the differential diagnosis for hypothyroidism?
Depression
Anaemia
Dementia
What is myxoedema?
- Rare severe form of hypothyroidism
- Cutaneous and dermal oedema because of increased deposition of connective tissue. These bind to water and produce non-pitting boggy oedema around eyes, feet, tibia, hands, supraclavicular fossa
How can hypothyroidism be classified?
Based on the time of onset: congenital or acquired (1)
The level of endocrine dysfunction:
Primary hypothyroidism - abnormality in thyroid gland itself
Secondary hypothyroidism - secondary to disorders of the pituitary or hypothalamus
The severity:
Overt hypothyroidism - TSH concentration is above the reference range (greater than10mU/L) & serum free T4 levels below the reference range
Subclinical hypothyroidism - serum TSH concentration is increased, serum free T4 concentrations are within the reference range (2)
Who gets pretibial myxoedema?
Pretibial myxoedema is nearly always associated with Graves disease.
What is the classic triad of signs of Graves disease?
Pretibial myxoedema
Ophthalmopathy (prominent eyes due to deposition of myxoedema behind the orbit)
Acropachy (swelling of distal digits with overgrown nail plates that may lift off the nail bed; similar to clubbing)
Go through the thyroid examination
- Inspection
i) Neck from front - goitre
ii) Asked to swallow - moves up- Palpation
i) Tenderness - movement with swallowing
ii) Size (soft/firm/hard) - nodular or diffuse
iii) Medial edge of SCM - lymph nodes - Percussion
i) Upper mediastinum - retrosternal goitre - Auscultation
i) Bruit - inspiratory stridor - Thyroid status
i) Exophthalmos/proptosis
ii) Lid retraction/ lid lad
iii) Conjunctival injection
iv) Periorbital oedema
v) Loss of movements
vi) Myxoedema
vii) Hyperactivity/restlessness
viii) Palm - warm/cold/sweaty
- Palpation
What are the features of acromegaly?
Coarse facial appearance, Spade-like hands
Increase in shoe size
large tongue, prognathism, interdental spaces excessive sweating and oily skin: caused by sweat gland hypertrophy features of pituitary tumour: hypopituitarism, headaches, bitemporal hemianopia
raised prolactin in 1/3 of cases → galactorrhoea
6% of patients have MEN-1
Common drug causes of gynaecomastia
spironolactone (most common drug cause) cimetidine digoxin cannabis finasteride gonadorelin analogues e.g. Goserelin, buserelin oestrogens, anabolic steroids
How long does Carbimazole take to lower free T4?
6 weeks
Why is propylthiouracil used more in pregnant women?
Doesn’t cross the placental barrier as much.
Carbimazole is a teratogenic and patient needs to be on contraceptive to get it
However PTU is only effective for 75 mins
