Endocrinology Flashcards
Outline the mechanism of primary hypothyroidism.
Low T4
High TSH and TRH
What are the causes of primary hypothyroidism?
Autoimmune: Hashimoto’s thyroiditis
Atrophic thyroiditis
Thyroidectomy
Radioactive iodine
Drugs
What is the management of primary hypothyroidism?
Replace thyroxine
Outline the mechanism of secondary hypothyroidism.
Pituitary gland failure
Low T4
TSH and TRH are low
Outline the mechanism of thyrotoxicosis.
Negative feedback loop
High T4
TSH and TRH are low
What are some of the causes of thyrotoxicosis?
Autoimmune: Graves’ disease
Multinodular goitre
Single toxic nodule
Thyroiditis: viral, post-partum, drugs
What is the management of thyrotoxicosis?
Beta-blocker for symptoms
Antithyroid medication: carbimazole
Radioactive iodine
Surgery
Outline the mechanism of a TSH-secreting pituitary tumour.
High T4
High TSH
Low TRH
What is the general theory behind dynamic testing?
If you think there is not enough hormone –> try to stimulate
e.g. short synacthen test, insulin tolerance test
If you think there is too much hormone –> try to suppress
e.g. glucose tolerance test, dexamethasone suppression test
What are the signs and symptoms of acromegaly?
Excess growth hormone production
- large, “spade-shaped” hands and feet
- coarse features: prominent supraorbital ridge, large nose, separated teeth, protruding jaw
- headache
- visual field defects: bitemporal hemianopia
- excessive sweating
- carpal tunnel syndrome
- cardiomegaly and hypertension
- glucosuria and polyuria
- abnormal glucose tolerance test
- arthrosis
- sexual dysfunction
- peripheral neuropathy
- galactorrhoea
Outline the hormones produced by the pituitary gland.
HYPOTHALAMUS PITUITARY GLAND END-ORGAN
GnRH LH & FSH Ovaries/testes (androgens –> sperm, oestrogens –> ovulation)
GHRH GH Liver (growth factor)
Dopamine (-)Prolactin Breasts/gonads (lactation)
TRH TSH Thyroid (thyroxine)
CRH ACTH Adrenals (steroid hormones)
ADH Renal tubules
Oxytocin Breasts/uterus
What are the investigations in acromegaly?
- TSH & T4
- prolactin
- FSH & LH
- GH
- insulin growth factor-1
- glucose tolerance test
- MRI pituitary fossa
What is the management of acromegaly?
Surgery: transphenoidal
Radiotherapy: conventional or gamma-knife
Medical: somatostatin analogue (octreotide), GRH blockers (pegvisomant)
What is growth hormone?
Peptide hormone causing musculoskeletal and vertebral growth and gluconeogenesis
Inhibited by somatostatin
Pulsatile
Glucose tolerance test: increases somatostatin –> should suppress GH
What does an excess or deficiency of growth hormone cause?
EXCESS
- children = gigantism (epiphyses fail to fuse)
- adults = acromegaly
DEFICIENCY
- children = proportional dwarfism
- adults = weight gain, muscle loss (insulin tolerance test - contraindicated in IHD and epilepsy)
What are the signs and symptoms of Cushing’s syndrome?
- plethoric, moon facies, dorsal hump
- bruising, thin skin, purpura, poor wound healing, abdominal striae
- central obesity
- cardiac hypertrophy and hypertension
- adrenal tumour/hyperplasia
- myopathy
- amenorrhoea
- diabetes
What is Nelson’s syndrome?
Development of ACTH-secreting tumour following bilateral adrenalectomy for Cushing’s disease
What are the investigations in Cushing’s disease?
- 24hr urinary cortisol x 3
- ACTH
- midnight cortisol
- low dose dexamethasone suppression test = 0.5mg qds 48hrs (excludes pseudo-Cushing’s)
What are the differentials for Cushing’s disease?
- ACTH secreting pituitary
- ectopic ACTH-secreting tumour
- adrenal tumour
Differentiate using high dose dexamethasone suppression test, CRH test, petrosal sinus sampling, MRI pituitary fossa
Contrast pituitary and adrenal Cushing’s.
Pituitary:
- high cortisol
- high ACTH
Adrenal:
- high cortisol
- low ACTH
Outline the mechanism of Addison’s disease.
Low steroid hormones
High ACTH
What are the signs and symptoms of Addison’s disease?
- hyponatraemia
- hyperkalaemia
- postural hypotension
- bronze pigmentation
- GI disturbance
- weight loss
- weakness
- hypoglycaemia
- change in distribution of body hair
What are the causes of primary adrenal insufficiency?
Autoimmune
TB
Iatrogenic
Sepsis
Infiltrative disease
Friedrich-Waterhouse syndrome (haemorrhagic adrenalitis, fulminant meningoccocaemia)
Adrenal leucodystrophy
What is the management of a hypoadrenal crisis?
- fluids
- glucose
- steroids: hydrocortisone 100mg IV 6hrly
- treat sepsis
- find cause
