Posterior pituitary pathology Flashcards
What is the more common name for arginine vasopressin deficiency?
Diabetes insipidus
What is diabetes insipidus?
This is a deficiency or insensitivity to ADH in the body
What are the 2 types of diabetes insipidus?
Central
Nephrogenic
What are some acquired causes of DI?
- Idiopathic
- Trauma (Road accidents, surgery, skull fracture)
- Tumours
- Hypophysitis
- Metastases
- Meningitis
What causes familial DI?
Familial DI is very rare and in most cases is isolated
It can, however, be caused by Wolfran syndrome, as part of the DIDMOAD effects:
- DI - Diabetes Insipidus
- DM - Diabetes Mellitus
- OA - Optic atrophy
- D - Deafness
What is central DI?
Central diabetes insipidus is a deficiency of ADH due to disfunction of the hypothalamus or posterior pituitary
What are the main causes of central DI?
- Trauma (Including surgery)
- Tumours
- Inflammatory disorders
How does nephrogenic DI occur?
This is caused by renal tubular resistance to the effects of ADH
What test is used to diagnose DI?
Water deprivation test
How is a water deprivation test performed?
- Check serum and urine osmolarity for 8 hours, and then 4 hours after giving desmopressin (DDAVP)
- If Ur:Serum osmolarity is >2, then it is normal
- If the ratio improves with DDAVP, then it is due to arginine vasopressin deficiency (Cranial DI)
- Differentiate from arginine vasopressin resistance (Nephrogenic DI)
What is the main calculation for estimating serum osmolarity?
2[K] + 2[Na] + [urea] + [glucose] = serum osmolarity
What are some causes of nephrogenic DI?
- Idiopathic
- Familial (AVPR2 receptor mutations)
- Renal disease
How does DI present?
- Polydipsia
- Polyuria with dilute urine
How is central DI managed?
Desmopressin
What are the 3 forms of desmopressin?
- Desmospray - Nasally 10-60mcg/day
- Desmopressin tablets - 100-1000mcg/day
- Desmopressin injection - 1-2mcg/day
How is nephrogenic DI managed?
There is no current pharmacological treatment for nephrogenic
What does SIADH stand for?
Syndrome of Inappropriate ADH secretion
What is SIADH?
This is a complex paraneoplastic syndrome in which the tumour secretes large amounts of Anti-Diuretic Hormone (ADH), resulting in hyponatraemia (Low sodium concentration)
What is the most common cause of SIADH?
Small cell lung cancer
How does SIADH present?
- Nausea
- Myoclonus (Sudden brief muscle twitching)
- Lethargy
- Confusion
- Seizures
- Possible coma
How is SIADH managed?
Fluid restriction and possible demeclocycline
