Diabetes Insipidus Flashcards
What is Diabetes Insipidus?
A lack of ADH or a lack of response to ADH.
What are the 2 Types of Diabetes Insipidus?
- Nephrogenic DI.
2. Cranial DI.
What is Nephrogenic DI?
The collecting kidneys do not respond to ADH.
Give 4 causes of Nephrogenic DI.
- Drugs e.g. Lithium.
- Mutation in AVPR2 Gene on X Chromosome (coding for ADH Receptor).
- Intrinsic Kidney Disease.
- Electrolyte Disturbance - Hypokalaemia and Hypercalcaemia.
How does Lithium cause Nephrogenic DI?
It desensitises the kidney’s ability to respond to ADH in the collecting ducts.
What is Cranial DI?
The hypothalamus does not produce ADH for the pituitary gland to secrete.
Give 7 causes of Cranial DI.
- Idiopathic.
- Brain Tumours.
- Head Injury.
- Brain Malformations.
- Brain Infections e.g. Meningitis, Encephalitis, TB.
- Brain Surgery/Radiotherapy.
- Haemochromatosis, Wolfram’s Syndrome, Sarcoidosis.
Give 5 key clinical features of Diabetes Insipidus.
- Polyuria.
- Polydipsia.
- Dehydration.
- Postural Hypotension.
- Hypernatraemia.
What is indicative of DI in Urine?
- High Plasma Osmolality.
2. Low Urine Osmolality (<700mOsm/kg).
Investigation of Choice in DI.
Desmopressin Stimulation Test (Water Deprivation Test).
What is the method for the DI Investigation of Choice? (4)
- Avoid fluid intake for 8 hours (fluid deprivation).
- Measure urine osmolality.
- Administer Synthetic ADH - Desmopressin.
- Measure urine osmolality 8 hours later.
Results of Desmopressin Stimulation Test (3).
OSMOLALITY :
- Nephrogenic - *Low; **Low.
- Cranial - *Low; **High.
- Primary Polydipsia - *High; **High.
* After Deprivation.
* * After Desmopressin.
Management of Diabetes Insipidus (3).
- Treat underlying cause.
- Mild - Conservative.
- Desmopressin - Cranial DI; Nephrogenic (In Higher Dose under Close Monitoring).
- Thiazide and Low Salt/Protein Diet - Nephrogenic.
