Endocrine #6 (SIADH and Diabetes Insipidus) Flashcards
ADH (Anti-Diuretic Hormone), or Arganine Vasopressin, is produced by the hypothalamus and stored in and released by the _______
Posterior pituitary
Most important role of ADH is to control the
Explain it in easy terms
Volume of fluid in the body
-Pituitary has osmoreceptors that can sense the volume in the body.
-Pituitary recognizes when the body is dehydrated, so it releases ADH.
-ADH tells the kidneys to retain water, the body is dehydrated.
-If the body is in fluid overload, it can slow down production of ADH and allow more volume to be released through urine
SIADH (Syndrome of Inappropriate Antidiuretic Hormone) is what?
Excess of ADH from pituitary gland or ectopic source leading to free water retention and hyponatremia due to the kidney’s inability to dilute the urine to excrete excess water
Etiologies of SIADH
-CNS (MC): Subarachnoid hemorrhage, stroke, head trauma, Meningitis, CNS tumors
-Pulmonary: Small cell lung cancer, infection (Legionella PNA)
-Meds: Anticonvulsants, HCTZ, NSAIDs, Antidepressants, Ecstasy, IV Cyclophosphamide
-Other: HIV, Hypothyroidism, Conn Syndrome
Big Three: SAH, SCLC, Anticonvulsants
Symptoms of SIADH
-Neurologic symptoms of hyponatremia and cerebral edema: Confusion, lethargy, AMS, disorientation, seizures, coma
Diagnostics for SIADH (what do the labs show)
-Normovolemic hypotonic hyponatremia (no signs of edema)
–Normovolemic: Patient will appear to be normal with no edema or swelling in the legs
–Hypotonic: low solute concentration. All the fluid is saved up in the body.
–Hyponatremia: all excess water relative to sodium amount
What other labs will be shown with SIADH (serum and urine)
-Decreased serum osmolarity
–watered down serum, low solutes (diluted)
-Increased urine osmolarity (concentrated urine)
–urine has little fluid, very concentrated
-Increased ADH
Treatment for SIADH
-Mild: Water restriction
-Moderate: ADH receptor antagonists (Conivaptan, Tolvaptan)
-Severe (Seizures, coma): IV hypertonic saline + Furosemide
-Chronic: Demeclocycline (inhibits ADH)
Although treating the underlying cause is the mainstay of treatment for SIADH, rapid correction >0.5 mEq/L/hr may lead to ______
central pontine myelinolysis
-Happens after correcting hyponatremia too rapidly.
-Confusion, balance problems, weakness in face, slurred speech
On the other hand, diabetes insipidus is not enough ADH. There are two types: Central and Nephrogenic. Explain them both.
Central: No production of ADH
Nephrogenic: Renal insensitivity to ADH
What are some causes of central DI?
This is the MC type.
-Idiopathic (MC), posterior pituitary destruction, head trauma, CNS tumor, Sarcoid granuloma
What are some causes of nephrogenic DI?
-Partial or complete insensitivity of the kidneys to ADH
–Lithium****
–Amphotericin B
–Hypokalemia or Hypercalcemia (disrupts kidney concentrating ability)
–ATN
–Hyperparathyroidism
Symptoms of Diabetes Insipidus
-Polyuria (up to 20 liters daily)
-Polydipsia (excessive thirst to maintain water balance)
-High volume nocturne
-Neuro symptoms of Hypernatremia: AMS when water intake is less than urinary water loss
-Dehydration, hypotension
What do labs for Diabetes Insipidus show (again, think of the serum and urine)
-Increased serum osmolarity
–Not retaining any water, concentrated in body, large solutes
-Decreased urine osmolarity and specific gravity, increased urine volume
–Tons of fluid in urine, not much solute
–Specific gravity: if well-hydrated, it’ll be higher. These patients are very dehydrated though, so decreased.
What test can you do for Diabetes Insipidus, to establish the diagnosis?
-Fluid deprivation test (to establish dx)
–Normal response: progressive urine concentration
–DI = continued production of large amounts of dilute urine (low urine osmolarity)
