Diabetes Insipidus

Question 1

What is diabetes insipidus (DI)?

Answer 1

A condition where the kidneys are unable to concentrate urine, leading to excessive urination and thirst

Question 2

Why can DI be life-threatening?

Answer 2

Severe dehydration and electrolyte imbalances can occur if fluid intake does not match urine output

Question 3

What are the two main types of diabetes insipidus?

Answer 3

Cranial (central) DI
Nephrogenic DI

Question 4

What is the underlying problem in cranial DI?

Answer 4

Insufficient circulating ADH (vasopressin)

Question 5

What is the underlying problem in nephrogenic DI?

Answer 5

The kidneys are resistant to ADH

Question 6

Name a common drug that can cause nephrogenic DI

Answer 6

Lithium toxicity

Question 7

What are the two hallmark symptoms of DI?

Answer 7

1. Polydipsia (excessive thirst)
2. Polyuria with dilute urine

Question 8

How does urine osmolality change after fluid deprivation in both cranial and nephrogenic DI?

Answer 8

It remains low in both conditions

Question 9

What happens to urine osmolality after desmopressin administration in cranial DI?

Answer 9

It increases significantly

Question 10

What happens to urine osmolality after desmopressin administration in nephrogenic DI?

Answer 10

It remains low due to impaired renal response to ADH

Question 11

What lab finding excludes DI during a water deprivation test?

Answer 11

Urine osmolality >700 mOsm/kg

Question 12

What imaging should be done if cranial DI is diagnosed?

Answer 12

MRI or CT of the brain to rule out tumors
(especially craniopharyngioma)

Question 13

What is the first-line treatment for cranial DI and how can it be given?

Answer 13

Desmopressin (DDAVP)

= given as a
(1) nasal spray
(2) oral tablet
(3) IM injection in emergencies

Question 13

Why does desmopressin not work in nephrogenic DI?

Answer 13

The kidneys are resistant to ADH

Question 14

How is nephrogenic DI managed?

Answer 14

Thiazide diuretics

Low salt/protein diet to reduce urine output

Question 15

How many litres of urine produced per day would be suggestive of diabetes insipidus?

Answer 15

3 or more litres

Question 16

Which drug commonly used for bipolar disorder can cause AVP resistance (nephrogenic diabetes insipidus)?

Answer 16

Lithium

Question 17

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?

Answer 17

AVP resistance (Nephrogenic diabetes insipidus)

Question 18

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?

Answer 18

Vasopressin analogue

Question 19

The fault in cranial DI relates to what problem?

Answer 19

posterior pituitary problem

Question 20

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?

Answer 20

water deprivation test

Question 21

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?

Answer 21

Lithium

= AVP resistance (nephrogenic diabetes insipidus)

Question 22

How do symptoms differ between nephrogenic DI (AVP resistance) and cranial DI (AVP deficiency)?

Answer 22

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

Question 23

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?

Answer 23

AVP Resistance

Question 24

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?

Answer 24

Thiazide diuretic

Question 25

How does the water deprivation test confirm cranial diabetes insipidus (CDI)?

Answer 25

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

Question 26

What urine osmolality changes confirm cranial DI in the water deprivation test?

Answer 26

If urine osmolality remains <300 mOsm/kg (often 200) after fluid deprivation but increases by >50% after desmopressin = 730 mOsm/kg or higher.

Question 27

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?

Answer 27

Desmopressin

Question 28

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?

Answer 28

Lithium can cause nephrogenic diabetes insipidus, so checking urine osmolality helps assess the kidney’s ability to concentrate urine and differentiate from other causes

Question 29

A 25-year-old female presents to her general practitioner with a 2-month history of polyuria, nocturia and chronic thirst. She suffered a concussion in a car crash, one month before the onset of her urinary symptoms. Amongst other investigations, she is referred for a water deprivation test. Given the likely diagnosis, what is this patient's water deprivation test likely to show?

Answer 29

Low urine osmolality after fluid deprivation, but high after desmopressin

Question 30

A 45-year-old male is investigated for polyuria. A water deprivation test is done to ascertain the cause. Water deprivation started at 8 am. (1) Plasma osmolality after 8 hours =305 mOsm/kg (2) Urine osmolality after 8 hours = 190 mOsm/kg (3) Urine osmolality after 4 hours after desmopressin = 575 mOsm/kg Based on the presumed diagnosis, what feature is this patient most likely to have in their past medical history?

Answer 30

cranial diabetes insipidus = Recent transsphenoidal pituitary surgery

Question 31

A 54-year-old man presents with excessive thirst, constant headaches and nausea. He states that his thirst persists despite drinking multiple bottles of water throughout the day. On examination, he appears euvolaemic when assessing hydration status and vital signs are within normal range. Investigations are arranged which show the following: Random urine osmolality 120 mOsm/kg (50-1200) Urine osmolality after fluid deprivation 695 mOsm/kg (50-1200) Urine osmolality after desmopressin 705 mOsm/kg (50-1200) What is the most likely diagnosis?

Answer 31

Primary polydipsia

Question 32

A 34-year-old woman is referred to Accident & Emergency from an inpatient psychiatric unit with a three-day history of polyuria. She also reports being excessively thirsty despite drinking lots of water. 4 weeks ago, she was diagnosed with epilepsy and bipolar disorder and was commenced on lithium and carbamazepine with good effect. Routine bloods performed by the psychiatry team are unremarkable, except for a sodium of 146 What is the next best investigation?

Answer 32

Since she's started on lithium = Urine and serum osmolality A water deprivation test can be done later for confirmation