What is diabetes insipidus?
Lack of ADH or lack of response to ADH
What causes cranial diabetes insipidus?
Hypothalamus does not produce enough ADH for the pituitary gland to secrete
- Brain tumours
- Head injury
- Brain malformations
- Brain infections (meningitis, encephalitis, TB)
- Brain surgery or radiotherapy
What causes nephrogenic diabetes insipidus?
Collecting ducts of kidney become unsensitised to ADH
- Lithium
- Mutations in AVPR2 gene that copes for ADH receptor
- Intrinsic kidney disease
- Electrolyte disturbance
What are the symptoms of diabetes insipidus?
- Polyuria
- Polydipsia
What are the tests that diagnose diabetes insipidus?
• Urine osmolarity
o Low
• Serum osmolarity
o High
• Water deprivation/desmopressin stimulation test
What is the water deprivation/desmopressin stimulation test?
o Patient avoids taking fluids for 8 hours
o Then urine osmolality is measures and synthetic ADH (desmopressin) is administered
o 8 hours later urine osmolality is measured again
How is cranial diabetes insipidus diagnosed after the water deprivation/desmopressin stimulation test?
After deprivation:
- Low
After ADH
- High
How is nephrogenic diabetes insipidus diagnosed after the water deprivation/desmopressin stimulation test?
After deprivation:
- Low
After ADH
- Low
How do you manage cranial diabetes insipidus?
Desmopressin
What is SIADH?
Inappropriate release of high levels of ADH
- Reabsorption of water from collecting ducts
- Urine has high sodium concentration or osmolarity
- Hyponatraemia (serum sodium is low)
What are the causes of SIADH?
- Atypical pneumonia
- Brain lesions – tumour, head injury and bleed, stroke
- Drugs – carbamazepine, SSRIs
- Malignancy – SCLC, GI, genitourinary, sarcoma, lymphoma
- Hypothyroidism
What tests do you do for SIADH?
- Fluid status
- Serum sodium
- Plasma osmolarity
- TFTs
- Serum cortisol
- Urine osmolarity
- Urine sodium
- CXR
What does fluid status show in SIADH?
Euvolemic or hypervolemic
What does serum sodium show in SIADH?
Low
What does plasma osmolality show in SIADH?
Reduced
What does urine osmolality show in SIADH?
High
How do you manage SIADH?
Fluid resuscitation
How do you manage nephrogenic diabetes insipidus?
Chlortalidone and NSAIDs
