Neurohypophysial disorders Flashcards

1
Q

Recall the pathophysiology of diabetes insipidus

A
  • Central (cranial): absence/lack of circulating vasopressin
  • Nephrogenic: end-organ (kidneys) resistance to vasopressin

Cycle:

  • Lack of VP
  • Increased urine excretion (polyuria)
  • Reduction in EC fluid volume
  • Increase in plasma osmolarity
  • Osmoreceptors trigger VP release
  • Triggers thirst
  • Increased drinking (polydipsia)
  • Decrease in plasma osmolarity
  • Expansion of EC fluid volume
  • Increased urine excretion (polyuria)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What are the principle causes of diabetes insipidus?

A

Cranial:

  • Damage to neurohypophysial system: injury, surgery, cerebral thrombosis, tumours, granulomatous infiltration of median eminence
  • Idiopathic
  • Familial (rare) - receptor gene mutations

Nephrogenic:

  • Familial (rare)
  • Drugs - lithium, dimethyl chlortetracycline
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What are the clinical features of diabetes insipidus?

A
  • Polyuria
  • Hypo-osmolar urine (v dilute)
  • Polydipsia
  • Dehyration if fluid intake not maintained (can –> death)
  • Possible sleep disruption
  • Possible electrolyte imbalance
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

How is diabetes insipidus diagnosed?

A
  1. Water deprivation test - should stimulate VP system - no/little change in urine osmolarity/VP
  2. Desmopressin (DDAVP) - like giving extra VP
    - Central - urine osmolarity increases bc VP receptors work fine and are stimulated by DDAVP
    - Nephrogenic - no effect bc they have VP anyway, it just has no effect
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

How is diabetes insipidus treated?

A
  • Desmopressin (DDAVP) for cranial - oral

- Thiazide diuretics for nephrogenic

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Recall the pathophysiology of SIADH

A
  • Plasma [VP] is inappropriately high for existing plasma osmolarity
  • Increased water reabsorption
  • Decreased plasma osmolality (hyponatraemia)
  • Decreased urine volume
  • Compensatory “escape” phenomenon - natriuresis + attempted restoration of urine output?
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What are the principle causes of SIADH?

A
  • Tumours (ectopic secretion)
  • Neurohypophysial malfunction (meningitis, cerebrovascular disease)
  • Thoracic disease (pneumonia)
  • Endocrine disease (Addison’s)
  • Physiological (hypovolaemia, pain, surgery)
  • Drugs (carbamezapine, SSRI)
  • Idiopathic
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What are the principle clinical features of SIADH?

A

Signs:

  • Raised urine osmolarity
  • Decreased urine volume (initially)
  • ***Hyponatraemia - decrease in plasma [Na] due to increased water reabsorption

Symptoms:

  • Can be asymptomatic
  • When [Na] falls <120mM - generalised weakness, poor mental function, nausea
  • When <110mM - confusion, coma, death
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

How is SIADH treated?

A
  • Once cause is identified, provide appropriate treatment, e.g. surgery
  • If someone already hyponatraemic, must treat this immediately: immediate fluid restriction; longer term, use drugs that prevent VP action in kidneys (lithium, dimethyl chlortetracycline, V2R antagonist - vaptans)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What are the principle actions of vasopressin?

A
  • Acts on renal cortical and medullary CDs
  • Stimulates synthesis and assembly of aquaporin 2
  • Increased water transport
  • Increased water reabsorption
  • Anti-diuretic effect
  • All above = V2
  • Vasoconstrictor activity - V1a
  • ACTH release - V1b
  • Factor VIII + VWF - V2
  • Central effects
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

Which receptors does vasopressin act on

A

V2 receptors

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What are the neurohypophysial hormones?

A

Vasopressin

Oxytocin

How well did you know this?
1
Not at all
2
3
4
5
Perfectly