W6 Diabetes Insipidus (PD) Flashcards
Diabetes insipidus stats (for info)
- caused by loss of ADH/AVP
- rare compared to Diabetes Mellitus
- similar prevalence in males and females
- prevalence 1 in 25,000
- occurs at any age
What is the cause of Diabetes Insipidus ?
- Lack of antidiuretic hormone (ADH)
- Reduced response to ADH
ADH = arginine vasopressin (AVP)
➢ AVP acts on the collecting ducts of the kidneys, allowing them to reabsorb water from urine.
- Binds to V2 receptors (GPCR) and inc expressions of aquaporins and effect on DCT
➢So having diabetes insipidus prevents kidneys from concentrating urine, which leads to:
▪ Polyuria = excessive urination
▪ Polydipsia = excessive thirst
Types of diabetes insipidus?
Nephrogenic (in kidneys)
* Condition also termed arginine vasopressin resistance
* Collecting ducts don’t respond to AVP
Causes:
* Drugs like lithium
* Electrolyte imbalance e.g. K+ and Ca2+
* Intrinsic kidney disease
* Genetic: AVPR2 gene on X chromosome
Cranial (in brain)
The hypothalamus does not produce AVP for the pituitary gland to
secrete
Causes:
* Idiopathic (no cause)
* Infections e.g. TB, meningitis, encephalopathy
* Brian tumour
* Head injury
* Surger
Diabetes Insipidus - Presentation
Polyuria
Polydipsia
Dehydration
Postural hypotension
Hypernatraemia
Increase in plasma osmolality can lead to:
Fatigue
Nausea
Poor concentration
Confusion
Diabetes Insipidus -
What are the investigations? (4)
- Urea and electrolytes (you may
find hypernatraemia) - Blood osmolality test (> 295 Milli
osmols/Kg) [normal range 285-
295 Mosm/Kg] - Urine test – output and
osmolality - Water Deprivation test
Water deprivation test – interpretation of results: Nephrogenic DI
Nephrogenic DI
* Patient unable to respond to ADH
* After 8 hrs water deprivation, urine
osmolality will still be low as the urine
is diluted with water secretion from
kidneys.
* After administration of desmopressin,
kidneys do not respond.
* After 8 hrs of the administration of
desmopressin, urine osmolality will
remain low
Water deprivation test – interpretation of results: Cranial DI
Cranial DI
* Patient lacks ADH but kidneys still
respond to ADH
* After 8 hrs water deprivation, urine
osmolality will still be low as the urine
is diluted with water secretion from
kidneys.
* After administration of desmopressin,
kidneys respond by reabsorbing
water and concentrating urine.
* After 8 hrs of the administration of
desmopressin, urine osmolality will be
high
Diabetes Insipidus - Treatment
for Cranial DI
What might be a possible side effect of desmopressin?
Identify cause (e.g. is it nephrogenic, etc.?)
Conservative treatment (i.e. no treatment), correct any underlying cause
Cranial DI –
Give Desmopressin (synthetic AVP) as patients lack AVP/ADH
* Desmopressin stimulates vasopressin V2 receptor in the principal cells of the late distal
tubule and collecting duct
* Increased insertion of aquaporins into the luminal membrane via a G-protein coupled
mechanism
* Increased permeability of the distal tubule and collecting duct to water
=Hyponatremia
Diabetes Insipidus - Treatment for Nephrogenic DI:
Renal cells generally unresponsive to desmopressin, but high dose can be
tried as partial response sometimes seen
Thiazide diuretics can be given (exact mechanism unclear)
* Increased sodium loss (in urine) causes reduced extracellular fluid
volume, reduced glomerular filtration and increased sodium and water
reabsorption in the proximal tubule
Non-steroidal anti-inflammatory drugs can also be used
Which of the following symptoms would suggest a diagnosis of diabetes insipidus?
A) High blood sugar levels
B) Excessive thirst and increased urine volume
C) Low blood sugar levels
D) Frequent urination and weight gain
E) Excessive sweating
= B
Mrs Rebecca McKenzie was diagnosed with central diabetes insipidus. The prescriber explained that in central diabetes insipidus, the blood and urine osmolality is typically:
A) Elevated, elevated, respectively
B) Within the normal range for both
C) Decreased, elevated, respectively
D) Highly variable for both
E) Elevated, decreased, respectively
=E
Mrs Rebecca McKenzie was diagnosed with central diabetes insipidus. Which diagnostic investigation will Mrs McKenzie be referred to, to confirm the diagnosis of diabetes insipidus? Select all that is relevant
A) Blood glucose test
B) Serum electrolyte levels
C) Urinalysis
D) Water deprivation test
E) Electrocardiogram (ECG)
= A-D
Patients with nephrogenic (arginine vasopressin resistant) diabetes insipidus and patients with central diabetes insipidus would be expected to have which AVP/ADH levels respectively
A. Low and low
B. Low and normal
C. Low and high
D. Normal and low
E. Normal and normal
F. Normal and high
Test Your Knowledge
G. High and low
H. High and normal
I. High and high
= G
