Diabetes Insipidus

Question 1

what is diabetes insipidus?

Answer 1

a disease characterised by the passage of large volumes (>3L/24hrs) of dilute urine (osmolality <300 mOsmol/Kg)

Question 2

what is the difference between neurogenic and nephrogenic diabetes insipidus?

Answer 2

• neurogenic diabetes insipidus occurs as a result of decreased circulating levels of vasopressin (ADH)
• nephrogenic diabetes insipidus occurs as a result of interference with the binding of ADH to its receptors or damage to the kidneys

Question 3

what are the causes of neurogenic diabetes insipidus?

Answer 3

• mutations in the vasopressin gene (e.g. autosomal dominant AVP-NPII)
• idiopathic
• tumour (e.g. pituitary adenoma, craniopharyngioma)
• trauma
• infection (e.g. meningitis)
• vascular (e.g. sheehan’s syndrome)
• sarcoidosis
• haemochromatosis

Question 4

what are the causes of nephrogenic diabetes insipidus?

Answer 4

• mutation (e.g. ADH receptor gene, aquaporin-2 gene)
• metabolic (e.g. hypercalcaemia, hyperglycaemia, hypokalaemia)
• drugs (e.g. lithium, demeclocycline)
• CKD
• amyloidosis
• post-obstructive uropathy

Question 5

what is dipsogenic diabetes insipidus?

Answer 5

a type of diabetes insipidus characterised by excessive thirst and fluid intake due to a malfunction in the thirst-regulating mechanism in the hypothalamus
- the patient, therefore, consumes large volumes of fluid, which suppresses the secretion of ADH and increases urine output

Question 6

what is primary polydipsia?

Answer 6

is characterised by an individual consuming large volumes of fluid and as a result producing large volumes of dilute urine

Question 7

what are the symptoms of diabetes insipidus?

Answer 7

• excessive urination (>3L/24hrs)
• excessive thirst
• nocturia
• dehydration (e.g. headache, dizziness, dry mouth)

Question 8

what are the signs on examination of diabetes insipidus?

Answer 8

• hypotension
• dilute urine
• dehydration (e.g. dry mucous membranes, prolonged CRT)

Question 9

what are the investigations for diabetes insipidus?

Answer 9

• 24-hour urine collection
• plasma glucose
• U&Es
• urine specific gravity
• plasma osmolality
• urine osmolality
• fluid deprivation test
• ? MRI brain
• ? US renal tract

Question 10

what is the management of diabetes insipidus?

Answer 10

• neurogenic: desmopressin
• nephrogenic: drink enough to satisfy their thirst, high-dose desmopressin is sometimes used for mild-to-moderate cases