Neurohypophysial disorders Flashcards
What two types of diabetes inspipdus are there?
How do they differ?
Cranial (central) DI
- No adequate secretion of VP
Nephrogenic
- kidneys can’t response to secreted ADH
What are possible causes of cranial Diabetes insipidus?
Most of the: aquired
Damage to the neurohyophysal system
- traumatic brain injury
- pituitary surgery
- pituitary tumors, metastisis spreading to pituitary
- Granulomatous infiltration of median eminence (i.e. inflammation)
Can be congenital (very rare)
What are possible causes of nephrogenic diabetis inspidus?
Congenital causes
- rare e.g. mutation in V2 receptors or aquaporin channels
Aquired
- drugs (e.g. lithium used in treatment of depression etc.)
What are the biochemical signs and symptoms of Diabetis inspidus?
Symptoms/Signs
- Polydipsia
- Polyuria
- Hypoosmolar urine
- Dehydration
Biochemical markers
- Hypernatraemia
- raised urea
- –> Both signs for dehydration
- High plasma osmolarity
Which tests would you do with someone you suspect to have diabetis insipidus?
Next to biochemical markers (HIgh NA+. high plasma osmolarity, high urea)
Water deprivation test
- Deprive people from water and regularly measure urine production, concentration, plasma osmolality, and body weight
- In the end: Administer ADH analogue (DDAVP)
- When loosind >3% of body weight : end of test (dehydreation)
Findings:
- When water deprived: DI patients no concentration of urine, in other patients (normal, psychogenic polydipsia) urine will be concentrated
- Administering DDAVP: nephrogenic and cranial can be differentiated
What is psychogenic polydipsia?
What are the consequences?
- Seen in psychiatric patients (might be due to anti-cholinergic drugs causing dry mouth)
- People who are told to “drink plenty”
–> Nothing wrong with body function, people just drink to much (–> pee a lot)
Leading to:
- Low plasma osmololity
- Low NA+
- Dilute urine
Which conditions could you suspect when a patient comes to you with polyuria and polydipsia?
What are the differential diagnosis
- Most common: Diabetis Mellitus
- rule out by test, glucose etc
- If not DM:
- Diabetis insipidus
- Psychogenic polydipsia
How could you treat cranial Diabetis inspipdus?
What is important after treatment?
Selective V2 agonst: Desmopressin (DDAVP) (ADH analogue)
- nasal administration (majority) (–> might be considered less important medication in hospital –> easity forgotton –> might cause death)
- Can also be orally or subcutaneous
Important:
- Tell patients to not drink that much anymore! Otherwise risk of hyponatraemia!
How could you treat nephrogenic diabetis inspidus?
Rhiazide diuretics
–> noone knows how and why this works
Possible mechanism:
High plasma osmolarity
How do you call a disease that casues too much ADH secretion?
What is its definition/characteristic?
Syndrome of Inappropriate ADH (SIADH)
the plasma vasopressin concentration is inappropriately high for the existing plasma osmolality
What are the symptoms and characteristics of SIADH?
- •can be symptomless
- •however if p[Na+] <120 mM: generalised weakness, poor mental function, nausea –> Na+ essential to maintain depolerisation etc. in neurones
- •if p[Na+] <110 mM: CONFUSION leading to COMA and ultimately DEATH
Biochemical characteristics:
- Hyerosmolar urine
- Hypoosmolar plasma
- Hyponatraemia
What are causes of SIADH?
CNS causes:
- stroke, tumor, trauma, sub-arrachnoid haemorrhage
Pulmonary disease
- Pneumonia, bronchiectasis
Malignancy
- ectopic ADH e.g. by small cell lung carcinoma
Drug-related
- Carbamazepine (seizure control) , SSRI (Selective Serotonin Reuptake Inhibitor)
Ideopathic
How would you treat SIADH?
- Appropriate treatment (e.g. surgery for tumour)
- To reduce immediate concern, i.e. hyponatraemia
- Immediate: fluid restriction
- Longer-term: use drugs which prevent vasopressin action in kidneys
- e.g. induce nephrogenic DI ie reduce renal water reabsorption - demeclocyline
- inhibit action of ADH - V2 receptor antagonists (VAPTANS)
Explain the use of Vaptans in SIADH
Non-competitive V2 antagonist
- inhibts AQP2 production and transport
- causing aquaresis: electrolyte sparing diuretic (only water)
–> very expensive is limiting current use
Which test should you always perform after diagnosing a patient with Diabetis insipidus?
Why?
Always perform imaging:
About 1/2 of cases: metastasis of systemic tumor spreading to neurohypophysis)
to rule out cancer cause