Diseases Of The Posterior Pituitary Flashcards
Learn about the diseases of the posterior pituitary
What are the two main diseases of the Posterior pituitary
- Diabetes Isipidus
2. Syndrome of inappropriate anti diuretic hormone secretion
What is diabetes insipidus
- ADH deficiency
2. ADH unresponsive
How is Diabetes isipidus defined?
Passage of large volumes of (greater than 3l/24hours) dilute urine (less than 300mOsm/kg)
It his two major forms:
1. Central (neurogenic, pituitary or neurohypophyseal) DI, decreased secretion of ADH
2. Nephrogenic DI, decreased ability to conc urine because of resistance to ADH action in the kidney
What are the signs and symptoms if DI
- Polyuria
- Polydipsia
- Nocturia
- Hypernatraemia
- Increased serum osmolality
- Decreased urine osmolality
How is DI diagnosed?
- 24 hour urine collection
- Serum electrolyte concentration
- Urinary specific gravity
- Plasma urinary osmolality
- ADH levels
What additional tests are carried out?
- Water deprivation test (Miller Moses) to ensure adequate dehydration and maximal stimulation of ADH for diagnosis.
- Pituitary studies
How do you distinguish between central DI and nephrogenic DI?
- Give the patient ADH and if urine osmolality increases then central DI (missing ADH)
- If urine osmolality doesn’t change then nephrogenic
Where is ADH made?
Made in the hypothalamus and stored in the posterior Pituitary.
What cause nephrogenix DI?
- Lithium
- Demeclocycline a form of tetracycline
- Hypercalcemia
- Sickle cell disease
What are the causes of central DI
- Neoplasm or infiltrative lesions
- Sarcoidosis
- Surgery
- Radiotherapy
- Head injuries
What are the causes of Nephrogenic DI?
- Hypercalcemia
- Sickle cell disease
- Drugs (lithium, demecycline, colchinine)
What is the treatment for Central DI
- Desmopressin intranasally
2. Vasopressin subcutaneous
What is the treatment for Nephrogenic DI
- Diuretics and amiloride (calcium sparing)
2. NSAIDs
Define SIADH
- Hyponatraemia and hypo osmolality resulting from inappropriate, continued secretion or action of ADH arginine vasopressin (AVP)
- Despite normal or increased plasma volume, which results in impaired water secretion
What are the features of SIADH
- Free water retention
- Extracellular fluid volume expansion
- No pedal oedema or hypertension
- Concentrated urine
- Hyponatraemia
- Uosm greater than 300
What are the symptoms of SIADH especially when Hyponatraemia is severe?
- irritability
- confusion
- seizures
When should you consider SIADH?
Consider SIADH in all cases of euvolemic Hyponatraemia.
What is the diagnosis of SIADH
- Hyponatraemia less 130mEqL
- Plasma osm less 270osmol/kg
- Small amounts of concentrated urine
- Inappropriate naturesis
- Low BUN
- Low uric acid
- Normal thyroid adrenal function
- Urine sodium of greater than 20mEq/L
What is the etiology of SIADH?
Pulmonary disorders: 1. Malignancies (oat cell) 2. TB, sarcoidosis 3. Lung abscess CNS disorders 1. Head injuries 2. Stroke
What drugs can cause SIADH
- Chlorpropamide
- Vincristine, Vinblastine, cyclophoshamide
- SSRIs (sertraline)
What is the management of SIADH
- Restrict fluids 800-1500mls daily
- Px demeclocyclicine
- Lithium
In severe confusion, convulsions: - Hypertonic saline IV in 3-4. hours
