DI/SIADH

Question 1

Define DI

Answer 1

Fluid imbalance– inability to retain fluid and lack of sugar in urine
excessive thirst and excretion of large amounts (>3L/day) of dilute urination (<300 mOsm/kg)

Question 2

Define C-DI

Answer 2

decreased ADH released from PP causing polyuria, polydipsia, nocturia

Question 3

where is the defect with C-DI

Answer 3

hypothalamus or PP not making enough ADH

Question 4

where is the defect with N-DI

Answer 4

kidney (collecting tubules or loop of henle) unresponsive to ADH

Question 5

expected labs with C-DI vs N-DI

Answer 5

Central labs: LOW BMP, UA and ADH
Nephrogenic labs: normal-high BMP, UA, ADH
Both: high serum osmo, low urine osmo, no response to water deprivation

Question 6

what causes thirst in DI

Answer 6

elevated serum Na (increased Osmo) stimulates thirst to replace urinary water loss

Question 7

sx of hyper-natremia

Answer 7

lethargy
weakness
edema
irritability
NM excitability

Question 8

exogenous ADH can help with which type of DI

Answer 8

Central DI

Question 9

expected result of fluid deprivation test in someone w/ DI

Answer 9

no response to water deprivation

Question 10

Define N-DI

Answer 10

kidney resistant to ADH–> decreased ability to concentrate urine
polydipsia, polyuria, nocturia

Question 11

3 must haves for SIADH diagnosis

Answer 11

hyponatremia (<135) with low serum Osm (<275)
urine Osm >100mOsm/kg
Also: normal thyroid, renal and adrenal fx and urine sodium >30

Question 12

ADH levels in DI vs SIADH

Answer 12

DI has inadequate ADH
SIADH has excess ADH

Question 13

SERUM vs Urine osmolarity in DI & SIADH

Answer 13

Serum: DI high (polyuria), SIADH low (oliguria)
Urine: DI low, SIADH high

Question 14

serum sodium in SI vs SIADH

Answer 14

DI: hypernatremia
SIADH: hyponatremia

Question 15

main treatment differences for DI vs SIADH

Answer 15

DI: desmopressin, HCTZ, chlopropamide
SIADH: fluid restriction

Question 16

relationship between ADH levels and urine production

Answer 16

increase in ADH= water retention/decreased urine production
no ADH= water voided and higher sodium concentration

Question 17

what is the most important physiologic stimulant of ADH

Answer 17

plasma osmolaLity

Question 18

cycle of ADH & plasma osmolali

Answer 18

increased ADH–> increased reabsorption–> decreased plasma osmolality–> decreased ADH release–> increased plasma osmolality

Question 19

clinical signs of DI

Answer 19

polyuria, polydipsia, nocturia
craving cold water
hypernatremia
dehydration

Question 20

causes of central/neurogenic vs nephrogenic DI

Answer 20

central causes: pit or hypo thalamus damage from trauma or surgery, autoimmune, tumors, drugs, vascular
nephrogenic causes: renal d/o or lithium therapy, congenital, electrolyte d/o, sickle cell

Question 21

what happens if someone can’t respond to thirst stimulation?

Answer 21

severe hypernatremia= increased mortality

Question 22

diagnostic for DI

Answer 22

water deprivation test +/- serum ADH
vasopressin test (IM)
MRI to evaluate pituitary

Question 23

what is the vasopressin test (IM)

Answer 23

give IM vasopressin to determine if central or nephrogenic DI
if urine output slows- Central Di
if it remains the same- Nephrogenic DI

Question 24

first line tx in Central vs Nephrogenic DI

Answer 24

central tx: desmopressin
nephrogenic: Diuretics- amiloride

Question 25

other treatments for C-DI

Answer 25

HCTZ diuretics–causes mild hypovolemia & proximal Na & H2O reabsorption (end result is less urine output
Chlorpropamide (2nd line)– causes partial release of ADH & can cause hypoglycemia
Carbamazepine– enhances response to ADH in partial C-DI
Clofibrate– can induce SIADH

Question 26

which medication can reverse lithium effect

Answer 26

Amiloride (diuretic)

Question 27

name the only other class of meds that can work on N-DI

Answer 27

NSAIDs– inhibits prostaglandin synthesis so it doesn’t antagonize ADH
Indomethacin > Ibuprofen

Question 28

which gramulomatous disease can cause C-DI

Answer 28

sarcoid

Question 29

what drugs can cause C-DI

Answer 29

alcohol
diphenylhydantoin (seizure med)

Question 30

Sx of SIADH

Answer 30

nausea/vomiting, cramps
depressed mood, irritable
confusion, hallucinations
seizures, coma
edema/wt gain

Question 31

conditions associated w/ SIADH

Answer 31

head trauma
malignant neoplasms (esp small cell lung CA)
pulmonary dz
CNS d/o
drugs

Question 32

lab findings w/ SIADH

Answer 32

low plasma Na, low plasma Osm, high urine Osm d/t disproportionate solute excretion w/o water

Question 33

tx for SIADH

Answer 33

fluid restriction (for chronic hyponatremia)- fluids 500ml less than output
hypertonic saline if severe CNS sx (emergencies)

also: vasopressin receptor antagonist or urea to increase solute load and increase water loss

Question 34

how does desmopressin (DDAVP) work?

Answer 34

acts on collecting duct causing non suppressible ADH activity–> inability to excrete ingested water (hyponatremia)
monitor Na+ after starting the medication!