What are the two main variants of diabetes insipidus?
What are the main causes of nephrogenic diabetes insipidus?
- Chronic renal failure
What are the two key causes of acquired diabetes insipidus?
In nephrogenic diabetes insipidus, what causes the condition?
Failure of the kidneys to respond to ADH
What is the general cause behind all types of cranial diabetes insipidus?
There is a failure of ADH production
What are the main causes of cranial diabetes insipidus?
- Granulomatous disease
How is serum osmolality calculated?
2(Na+ + K+) + Glucose + Urea
Which condition which may induce cranial diabetes insipidus is associated with acute onset?
What is apoplexy?
Unconsciousness or incapacity resulting from a cerebral haemorrhage or stroke
How can diabetes insipidus be diagnosed?
Water deprivation test
Urine osmolarity is monitored when fluids are deprived
Urine fails to concentrate in DI
How can nephrogenic DI be differentiated from cranial DI?
Administer desmopressin (DDAVP)
- Cranial DI - Urine will concentrate in water deprivation
- Nephrogenic DI - Urine will fail to concentrate (kindneys are unresponsive to ADH or analogues)
In a patient with suspected panhypopituitarism, which clinical test is essential and what does it establish?
Visual field examination
Any development of bitemporal hemianopia
(due to compression of tumour on optic chiasm)
What is Addison's disease?
Primary autoimmune adrenal insufficiency
Addison's disease can result in deficiency of which hormone types?
Why is the impactation on androgen production in Addison's disease worse for women than it is for men?
In men adrenal androgens are fairly insignificant
The vast majority of androgens (such as testosterone) are made in the testes
How may Addison's disease present biochemically?
- Low Na+
- High K+
Why is there low sodium and high potassium in Addison's disease?
Aldosterone (a mineralocorticoid) is deficient
Aldosterone normally acts on the kidneys to cause sodium retention and potassium excretion
Which antibodies are associated with Addison's disease?
When cortisol levels supposed to be high and low?
- High in the morning
- Low in the evening
(also high in times of stress)
In order to diagnose Addison's disease what test is required and how would it be carried out?
Cortisol stimulation test
- Synacthen is administered
- Cortisol levels are measured at 30 and 60 minutes
- Failure for cortisol levels to rise sufficiently is diagnostic
A normal response is defined as a 30 minute serum cortisol concentration greater than 420 nmol/L
Why do patients with Addison's disease have skin pigmentation?
- Low cortisol levels cause the pituitary to produce more hormone in an attempt to compensate for low cortisol
More ACTH is produced via the precursor proopiomelanocortin
- Proopiomelanocortin is also the precursor for melanocyte stimulating hormone causing increased melanin production
What is the most important treatment to give in patients with Addison's disease and why?
Hydrocortisone (cortisol replacement)
Glucocorticoids are the most essential hormones to maintain life
What is the biochemical pattern of Conn's syndrome?
- Normal-high sodium
- Low potassium
What is Conn's syndrome?
How can Conn's be treated pharmacologically?
Which condition is associtaed with the following biochemistry?
- Low sodium
- Low potassium
- High urine sodium
- Low serum osmolarity
What are the diagnsotic criteria for DKA?
- Bicarbonate < 15mmol/l
- Ketones ++/+++ or >3 (serum)
Why may someone with an Addisonian crisis present with hypovolaemia?
Vomiting and diarrhoea
In DKA it is essential to replace what?
Why is a low potassium (for example after DKA) dangerous?
It can cause arrhythmias and death