Disorders of the posterior pituitary and hypothalamus Flashcards
What are the main disorders of posterior pituitary?
ADH deficiency and ADH excess.
Central diabetes insipidus - Inability to concentrate urine. 1.010 spec density of urine.
SIADH - seen in the elderly and by far most common cause is pharmacologic, from a bunch of different common drugs used in that population. From disease, it is frequently caused by SCC of the lung. Can also be caused by local hypothalamic injury.
Symptoms of SIADH
– fluid retention
– serum hypoosmolality
– dilutional hyponatremia
– hypochloremia
– concentrated urine in the presence of normal or increased intravascular volume
– normal renal function
– low Urine output
– increased body weight without edema
Causes of SIADH?
pulmonary conditions-pneumonia, TB, lung abscesses, Positive pressure ventilation
– Trauma (most frequently head related)
– meningitis, subarachnoid hemorrhage
– AIDS, Addison’s disease
– peripheral neuropathy, psychoses
– vomiting, stress and many medications
– symptoms may also be caused by ADH secreting tumors
Severe symptoms of SIADH and dilutional hyponatremia?
– cerebral edema occurs
– lethargy
– anorexia
– confusion
– headache,
seizures, coma and possibly death if untreated
How is SIADH diagnosed?
Diagnosis of SIADH is made by simultaneous measurement of urine and serum osmolality
– A serum osmolality lower than the urine osmolality indicates the inappropriate excretion of concentrated urine in the presence of very dilute serum
– Dilutional hyponatremia is indicated by serum sodium less than 134 mEq/l, serum osmolality less than 280 mOsm/kg, and specific gravity less than 1.005
Progression of symptoms in SIADH
– initally
- thirst,
- dyspnea on exertion,
- fatigue and dulled sensorium
– as serum sodium falls below 120mEq/l
- symptoms are more severe with
- vomiting
- abdominal cramps, muscle twitching
- seizures
- other Labs include decreased BUN, creatinine clearance
Treatment for SIADH
With mild symptoms and sodium above 125 mM,
- Just restrict fluid intake
- weight should gradually rise and so should serum sodium and osmolality
More severe symptoms or no improvement:
- IV 3-5% (hypertonic saline solution)
- Diuretic drugs - Lasix (furosemid) is the most often one, and it does not spare potassium, so potassium may need to be replaced.
Chronic SIADH
- Stadol: inhibits ADH secretion from the pituitary
- Declomycin: a tetracycline that causes nephrogenic diabetes insipidus, blocking the ADH signaling in the renal distal and collecting tubules.
Summary card SIADH
diagnostic criteria
- – hypotonicity of plasma
- – hyponatremia
- – less than max dilute urine •
treatment
- – water restriction 600- 800 ml/day
- – Demeclocycline urine (Declomycin) 900 -
- – natriuresis
- – exclusion of other causes (Declomycin) 900 - 1200 mg/day- blocks vasopressin at DCT
- – hypertonic saline if sodium < 115 mEq/L
What are the ADH receptors?
V1a V1b V2 and V3
all of them are GPCR
V2 is the main one in the kidneys. Increases AQP insertion to duct.
ADH effects on the kidney
Increases AQP expression and water resorption
Increases urea and sodium resorption into the medullary interstitium to further increases concentrating ability.
Does not produce vasoconstriction except in pharmacological doses, not physiological doses. That is up to AngII
Causes and types of diabetes insipidus
tumor,
granuloma,
inflammation,
trauma,
surgery,
vascular
– Pituitary (central or neurogenic)
– Renal (Nephrogenic)
– Psychologic (psychogenic)
Diabetes insipidus characteristics
- – the excretion of large quantities of urine (5-20 liters/day)
- – urine has low specific gravity (less than 1.003)
- – urine osmolality of less than 100 mOsm/kg
- – Serum osmolality is greater than 295 mOsm/kg
- – in the milder form urine output may be only 2-4liters/day
- – the client compensates by drinking large amounts of water so that serum osmolality is normal or only moderately elevated
Associated features:
visual field loss, optic atrophy, papilledema (optic nerve swelling), other pituitary hormone abnormalities
What are the symptoms of diabetes insipidus?
- Severe fluid volume deficit results in –
- hypovolemia –
- poor tissue turgor –
- hypotension –
- tachycardia –
- constipation –
- signs of shock,
- CNS manifestations – irritability – mental dullness – coma •
These symptoms are a result of rising serum osmolality and hypernatremia, and hypovolemia
Treatment for diabetes insipidus
Administer fluids, saline and glucose
ADH replacement, can be IV, Sub cu, or IM
Needs to be administered slowly , increasing serum sodium concentration by 1mM every 2 hours, to prevent osmotic demyelination of the CNS.
Long term treatment is ADH replacement, with DDAVP, Desmopressin acetate. An ADH analog that does not have the vasoconstrictive effects. Administered intranasally.
Disorders of the hypothalamus
Kallmann syndrome
Laurence Moon Biedl syndrome
Frohlich syndrome
Prader Willi
Acquired diseases
- tumors, cyst, vascular lesion, granuloma, trauma, irradiation, inflammation
