Water Regulation Conditions

Question 1

What is diabetes insipidus?

Answer 1

Lack of ADH or lack of response to ADH, leading to the inability of the kidneys to conserve water, which then leads to frequent urination and pronounced thirst

Question 2

What are the two classes of diabetes insipidus?

Answer 2

Cranial

Nephrogenic

Question 3

Describe the pathophysiology of cranial diabetes insipidus

Answer 3

Hypothalamus fails to produce ADH

Question 4

Describe the pathophysiology of nephrogenic diabetes insipidus

Answer 4

Collecting ducts of the kidneys fail to respond to ADH

Question 5

What are the causes of cranial DI?

Answer 5

Idiopathic

Brain tumours

Surgery

Radiotherapy

Head trauma

Meningitis, encephalitis, TB

Hypopituitarism

Question 6

What are the causes of nephrogenic DI?

Answer 6

Hypercalcaemia

Hypokalaemia

Drugs

• Demeclocycline
• Lithium

Chronic renal disease

Question 7

How does DI present?

Answer 7

Polyuria

Polydipsia

Dehydration

Postural hypotension

Hypernatraemia

Question 8

What investigations are used in DI diagnosis?

Answer 8

Low urine osmolality

High serum osmolality

Water deprivation test

Question 9

Describe the water deprivation test

Answer 9

Patient should avoid drinking fluids for 8 hours

Urine osmolaity is measured

ADH is administered

Urine osmolaity is measured again 8 hours later

Question 10

Describe water deprivation test results

Answer 10

In cranial diabetes insipidus, urine osmolality will start as low and then increase as kidneys can still respond to the ADH

In nephrogenic diabetes insipidus, urine osmolality will start as low and stay low as the kidneys are unable to respond

In primary polydipsia, urine osmolaity will be high before and after ADH administration

Question 11

How is cranial DI managed?

Answer 11

Desmopressin (ADH analogue)

Question 12

How is nephrogenic DI managed?

Answer 12

Treat underlying cause

Thiazide diuretics (paradoxical effect)

Question 13

Give causes of hyponatraemia (urinary Na > 20mmols)

Answer 13

Renal loss (hypovolaemic)

• Thiaides and loop diuretics
• Addisons
• Renal failure

Euvolaemic

• SIADH
• Hypothyroidism

Question 14

Give causes of hyponatraemic (urinary Na <20mmols)

Answer 14

Extra renal loss of Na

• Diarrhoea, vomiting, sweating
• Burns

Water excess (hypervolaemic)

• HF, liver cirrhosis
• Nephrotic syndrome
• IV dextrose
• Psycogenic polydipsia

Question 15

How does hyponatraemia present?

Answer 15

Headache

Fatigue

Muscle cramps

Confusion

Seizures and reduced consciousness if severe hyponatraemia

Question 16

How is hyponatraemia managed?

Answer 16

Mild (130-134)

• Fluid restriction, less than 800ml/day
• Loop diuretics

Moderate (120-129)

• Hypertonic (3% NaCl) saline first 3-4 hours
• Rest is the same as mild

Severe (<120)

• Bolus of hypertonic saline until symptom resolution
• Conivaptan

Question 17

Give a complication of hyponatraemia

Answer 17

If Na+ increases too rapidly, central pontine myelinolysis/osmotic demyelination syndrome

Usually fatal and can result in locked in syndrome