Diabetes Insipidus Flashcards
Pituitary Disorder
What is diabetes insipidus (DI)?
A condition where the kidneys are unable to concentrate urine, leading to excessive urination and thirst
Why can DI be life-threatening?
Severe dehydration and electrolyte imbalances can occur if fluid intake does not match urine output
What are the two main types of diabetes insipidus?
Cranial (central) DI
Nephrogenic DI
What is the underlying problem in cranial DI?
Insufficient circulating ADH (vasopressin)
What is the underlying problem in nephrogenic DI?
The kidneys are resistant to ADH
Name a common drug that can cause nephrogenic DI
Lithium toxicity
What are the two hallmark symptoms of DI?
- Polydipsia (excessive thirst)
- Polyuria with dilute urine
How does urine osmolality change after fluid deprivation in both cranial and nephrogenic DI?
It remains low in both conditions
What happens to urine osmolality after desmopressin administration in cranial DI?
It increases significantly
What happens to urine osmolality after desmopressin administration in nephrogenic DI?
It remains low due to impaired renal response to ADH
What lab finding excludes DI during a water deprivation test?
Urine osmolality >700 mOsm/kg
What imaging should be done if cranial DI is diagnosed?
MRI or CT of the brain to rule out tumors
(especially craniopharyngioma)
What is the first-line treatment for cranial DI and how can it be given?
Desmopressin (DDAVP)
= given as a
(1) nasal spray
(2) oral tablet
(3) IM injection in emergencies
Why does desmopressin not work in nephrogenic DI?
The kidneys are resistant to ADH
How is nephrogenic DI managed?
Thiazide diuretics
Low salt/protein diet to reduce urine output
How many litres of urine produced per day would be suggestive of diabetes insipidus?
3 or more litres
Which drug commonly used for bipolar disorder can cause AVP resistance (nephrogenic diabetes insipidus)?
Lithium
A 48-year-old female is admitted to the acute medical ward having been admitted in a confused state. She has a background of bipolar disorder and takes lithium. Blood tests reveal lithium toxicity and she is treated supportively. Following catheterisation it is noted that the patient is passing 3 litres of urine each day.
The FY1 doctor sends a urine sample for osmolality and results show a low osmolality (220 mOsm/kg).
What is the most likely diagnosis?
AVP resistance (Nephrogenic diabetes insipidus)
A 58-year-old male is involved in a head-on road traffic accident. He is brought to the hospital with a GCS of 8. A CT head shows extradural and subdural haematomas and he is transferred to the care of the neurosurgical team. Three days after admission he is noted to be polyuric, passing 4.5 litres of urine each day, initial urine osmolality is 284 mOsm/kg.
A water deprivation test is performed. Urine osmolality after fluid deprivation is 280 mOsm/kg. Urine osmolality following administration of desmopressin is 600 mOsm/kg.
Given the likely diagnosis, what is the correct management?
Vasopressin analogue
The fault in cranial DI relates to what problem?
posterior pituitary problem
A 33-year-old woman presents with polyuria and thirst, urinating several litres per day. It is getting in the way of her work and she does not know what to do about it. She has a past medical history of sarcoidosis which is managed conservatively and takes no regular medication.
What is the best diagnostic test?
Fluid deprivation test
A 55-year-old woman presents to her GP with nocturia and excessive thirst.
She is on the following medications:
carbamazepine
diazepam
lithium
propranolol
tramadol
What is the most likely cause of her symptoms?
Lithium
= AVP resistance (nephrogenic diabetes insipidus)
How do symptoms differ between nephrogenic DI (AVP resistance) and cranial DI (AVP deficiency)?
Both cause polyuria and polydipsia, but only cranial DI improves with desmopressin, while nephrogenic DI does not due to kidney resistance to ADH.
Severe nephrogenic DI may also cause (1) dehydration
(2) hypernatremia
(3) failure to thrive
(4) especially in infants
A 40-year-old patient presents with a history of frequent urination and excessive thirst. The patient reports that these symptoms have been ongoing for several months, with no significant changes in fluid intake or diet. They have also experienced episodes of dizziness and have noted a general feeling of weakness. A water deprivation test was performed, but despite this, the patient’s urine osmolality remained low.
What could be a potential underlying cause?
AVP Resistance
A 36-year-old male presents to the GP practice complaining of increased urinary frequency and increased thirst. He is currently passing urine 15-20 times per day and is having to wake up at night to go to the toilet also. The urine is described as very dilute. He is otherwise clinically well with no other lower urinary tract symptoms. He has a background of asthma, for which he takes regular inhalers, and bipolar affective disorder, for which he is on lithium.
Given the likely diagnosis, what is the most appropriate medical management?
Thiazide diuretic
How does the water deprivation test confirm cranial diabetes insipidus (CDI)?
In CDI, urine osmolality remains low after water deprivation but increases significantly after desmopressin administration.
This shows that the kidneys can respond to ADH, confirming a deficiency in ADH production
What urine osmolality changes confirm cranial DI in the water deprivation test?
If urine osmolality remains <300 mOsm/kg (often 200) after fluid deprivation but increases by >50% after desmopressin = 730 mOsm/kg or higher.
A 61-year-old female is referred to an endocrinology clinic with polydipsia. She has a background of asthma, type II diabetes, and haemochromatosis. A water deprivation test shows a high starting plasma osmolality and a final urine osmolality of 220 mOsm/kg. She is administered desmopressin, following which the urine osmolality increases to 730 mOsm/kg.
Given the most likely diagnosis, which is the most appropriate management option for this patient?
Desmopressin
A 34-year-old woman on lithium presents with polyuria and excessive thirst. Sodium is 146. The next best investigation is Urine and serum osmolality, explain why?
Lithium can cause nephrogenic diabetes insipidus, so checking urine osmolality helps assess the kidney’s ability to concentrate urine and differentiate from other causes
