Diabetes Insipidus (DI) Flashcards
Pathophysiology:
What hormones fails?
ADH - antiduretic hormone
Pathophysiology:
What does a central/cranial cause mean?
What does a nephrogenic cause mean?
ADH deficiency
ADH resistance
What is the function of ADH?
Increases the amount of water reabsorbed in the distal convoluted tubule and collecting duct.
Central Causes:
Tumours - what type?
List some other causes?
What granulomatous disease could cause this?
Stalk lesion, mets
Acute trauma
SAH
CNS infection
Autoimmune damage
Sarcoidosis
Nephrogenic causes:
What electrolyte if low could cause this?
What electrolyte if high could cause this?
Hypokalaemia - reduction in urinary concentrating ability and a lack of response to the antidiuretic hormone arginine vasopressin (AVP), resulting in nephrogenic diabetes insipidus
Hypercalcemia can cause renal dysfunction
Nephrogenic causes:
What drug used to treat bipolar disorder can cause this?
What long term kidney disease could cause this?
Lithium - Long-term lithium use can damage the cells of the kidneys so they no longer respond
Chronic kidney disease
S+S:
Knowing why it happens, list some common symptoms?
Why do they get hypernatraemia?
What are some CNS symptoms of hypernatremia?
Polydipsia*** - can be very severe
Polyuria - very dilute
Nocturia
Dehydration
Extreme dehydration can lead to hypernatremia, a condition in which the sodium concentration of the serum in the blood becomes very high due to low water retention. The cells of the body also lose water.
Irritability
Hypertonia
Differentials:
What is psychogenic polydipsia?
Psychogenic polydipsia is an uncommon clinical disorder characterized by excessive water-drinking in the absence of a physiologic stimulus to drink. The excessive water-drinking is well tolerated unless hyponatraemia supervenes
Investigations:
What needs to be checked to rule out diabetes mellitus?
Over how many litres is classed as polyuria?
Osmolality is the concentration of a solution expressed as the total number of solute particles per kilogram.
Knowing this, what would you expect the plasma osmolality to be?
What would you expect the urine osmolality to be?
What is primary polydipsia without DI associated with?
Glucose
> ## 3L a dayNormal/high - due to less water in the plasma, the solutes are going to be concentrated.
Low - as there is excess water so solutes are diluted.
Schizophrenia and mania
Investigations - Water Deprivation Test:
How long does the test last for?
What will happen to the plasma osmolality when the patient is dehydrated in DI?
What will happen to the plasma osmolality when the patient is dehydrated in primary polydipsia?
What is the name of the synthetic ADH that is given?
What is the osmolality of the urine in DI?
What will happen if it is a central DI cause?
What will happen if it is a nephrogenic cause?
What percentage of body weight would be lost before the test is stopped?
8 hrs
Increased plasma osmolality - due to loss of excess water
Normal - the kidneys are able to concentrate urine as ADH is normal so no loss of excess water.
Desmopressin
Low urine osmolality whereas high plasma sodium and increased plasma osmolality.
The kidneys will respond
The kidneys won’t respond
ADH is hard to measure and so it’s not part of the diagnostic process
> 3% body weight lost
Management:
Treatment of central DI?
Treatment of nephrogenic DI:
- What type of diet is used? - 2
- Why is bendroflumethiazide used?
TREAT CAUSE IN BOTH CASES
Desmopressin (synthetic ADH)
Low sodium diet and high fluid intake
A thiazide diuretic, such as chlorthalidone or hydrochlorothiazide, can be used to create mild hypovolemia which encourages salt and water uptake in the proximal tubule and thus improve nephrogenic diabetes insipidus.
