ENDOCRINE: Diabetes insipidus Flashcards Preview

Year 3 Medicine Block > ENDOCRINE: Diabetes insipidus > Flashcards

Flashcards in ENDOCRINE: Diabetes insipidus Deck (17)
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1
Q

What is osmolality?

A

How salty the blood is, low osmolality means less salt

2
Q

What is diabetes insipidus caused by?

A

Vasopressin deficiency - cranial DI,

or vasopressin resistance - nephrogenic DI.

3
Q

What is seen in biochemistry of DI?

A

High serum osmolality, low urine osmolality and high urine volume

4
Q

What is cranial DI caused by?

A
Pituitary disease 
Brain tumours 
Head injury 
Brain malformation 
Brain infections 
Genetic causes - strong FHx
5
Q

What is nephrogenic DI caused by?

A

Metabolic and electrolyte disturbance
Renal disease
Drugs affecting the kidney e.g. lithium

6
Q

What values of urine volume confirm DI?

A

> 3L in 24hrs in the presence of high serum osmolality and low urine osmolality

7
Q

What values of serum osmolality and urine osmolality confirm DI?

A

serum osmolality >295mosmol/kg and urine osmolality <300mosmol/kg

8
Q

What value of urine osmolality or serum osmolality can exclude diagnosis of DI?

A

Urine osmolality >600mosmol/kg

Double serum osmolality

9
Q

What investigation might you do for suspected DI?

A

Water deprivation test

10
Q

How do you conduct the water deprivation test?

A

Patient fluid deprived for 8 hours
Then urine osmolality is measured
Synthetic ADH is administered
8 Hours later urine osmolality is measure again

11
Q

What results would you expect on the water depravation test for cranial DI?

A

Initially low urine osmolality, then post-ADH administration high urine osmolality as cells of collecting duct are responding to the synthetic ADH

12
Q

What results would you expect on the water depravation test for nephrogneic DI

A

Low urine osmolality both pre and post ADH, due to the cells of the collecting duct not being able to respond to ADH

13
Q

How is cranial DI managed?

A

Investigate for pituitary disease

Give synthetic vasopressin - desmopressin

14
Q

How does overtreatment of DI with desmopressin present?

A

Get dilutional hyponatrameia - so get headaches, reduced cognitive ability, seizures

N.B.desmopressin= synthetic ADH, overtreatment leads to increased reabsorption of water therefore leading to the dilutional hyponatraemia

15
Q

How does undertreatment of DI with desmopressin present?

A

Excessive thirst, polyuria

16
Q

How is nephrogenic DI managed?

A

Find cause and reverse if possible.
Use of low salt, low protein diet, diuretics, NSAIDs
Keep on top of the thirst and replace water lost

17
Q

What are the differentials of Diabetes Insipidus clinical presentation?

A

Psychogenic polydipsia, DM, Diuretic use, Hypercalcaemia ( as serum calcium is elevated)

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