(!) SIADH

Question 1

Define SIADH

Answer 1

Syndrome of inappropriate ADH
characterised by pathologic increase of ADH secretion, resulting in concentrated urine and diluted blood

Pseudo SIADH-gain of function mutation that causes the V2 receptor to always be active-

Question 2

Aetiology and risk factors of SIADH

Answer 2

ADH acts in collecting tubules, causing reabsorption of Water, causing hyponatremia. The high serum volumes also shuts off RAAS-reinforcing hyponatremia
During illness, the pit gland can release ADH with no regards of regulation
Pulm infections, pull cancers(most common)
Malignancies-small cell lung cancer
CNS dysf-trauma, subdural/SAH, MS,
Aneathesia
Drugs-SSRI, NSAIDS

risk factors
Age >50
Lung infections
Being in nursing home
malignancy
CNS
medication related

Question 3

Epidiemology of SIADH

Answer 3

Most common cause of hyponatremia in patients with cancer
and accounts for about 30% of all hyponatremia (which is the most common electrolyte imbalance)

Most common causes are resp disease, cancer and then CNS disease

Question 4

Signs and Sx of SIADH

Answer 4

Focus on signs of hyponatremia-which often are cerebral oedema
Nausea, vomiting, headache, altered mental status
Seizures, comas

ENQUIRE ABOUT RECENT DIURETIC USE

Examinations-patients should be euvalemic-signs of hyper (swelling, etc), or hypo (tachycardia, dry mucous, sunken eyes) go against SIADH
No signs of adrenal insufucency (hypotenuse, weight loss, pigmentation of skin)

tends to only last as Long as cause

Question 5

Investigations of SIADH

Answer 5

Serum sodium-low-under 135
Serum osmolarity-low, under 275
Urine Sodium-raised (over 30)
Urine osmolarity-raised over 100

Question 6

Management of SIADH

Answer 6

Remedy hyponatremia, and cure what caused it

acute-hypertonic saline
CARE-aggresive saline can cause central pontine myelinolysis (CPM)-demyelination of pontine, basal ganglion, and cerebellar regions with resultant neurological symptoms,

Chronic severe hypo-
Hypertonic saline,
V2 receptor antagonists-vaptans
furosemide can help

mild/moderate SIADH-
Vaptans

if SIADH but no hyponatremia-lower water intake

SIADH disappears after cause is treated

Question 7

Complications of SIADH

Answer 7

Cerebral pontine myelonolysis
Aggressive correction of Hyponatremia can cause cells that had adapted to shrink-causes CPM

demyelination of pontine, basal ganglion, and cerebellar regions with resultant neurological symptoms,ncluding behaviour disturbances, lethargy, dysarthria, dysphagia, paraparesis or quadriparesis, and coma

malnutrition, potassium depletion and liver failure also can occur in CPM

to correct-water (oral) or hypotonic IV

Question 8

Prognosis of SIADH

Answer 8

If the underlying cause is treated-then SIADH tends to disappear
If the cause persists/can’t be cured-difficult to manage, need fluid restriction and medication

but vaptans seem to have a lot of disease associated with em-care