SIADH (Syndrome of Inappropriate ADH)

Referring to the algorithm for hyponatremia , the most common cause of euvolemic hyponatremia is SIADH, a state of positive water balance rather than sodium depletion. Normally, ADH is secretion is triggered by high plasma osmolality or low blood volume. However, in SIADH, other causes are responsible for hormone secretion. Often, the plasma osmolality is more dilute than the urine osmolality. In all cases, the urine osmolality is disproportionately high for a given plasma osmolality. Sodium output is higher than expected for a given plasma sodium level. The most common causes of SIADH are brain infections and surgery, neoplasm, and drug side effects. A long list of possible etiologies is listed below. Treatment usually consists of restriction of water intake to daily insensible losses. If the serum sodium is below 120 or if the patient is seizing, emergency treatment is administration of 3% sodium chloride solution to raise the serum sodium to 125. If the patient has evidence of fluid overloading, a history of CHF, or is resistant to treatment, loop diuretics may be added as well. Chronic treatment may involve administration of lithium or demeclocycline which inhibit ADH action.

Etiologies

CNS Pulmonary Neoplastic Pharmacologic

Infection
meningitis

encephalitis

abscess

Hypoxia-Ischemia
Trauma
Cerebrovascular accident
Tumor
Psychosis (dypsogenic)
Guillain-Barre syndrome
Vasculitis
VA shunt obstruction
cavernous sinus thrombosis
stress
Infection
bacterial

mycoplasma

fungal

viral

bacterial

Decreased left atrial pressure
pneumothorax

atelectasis

asthma/bronchiolitis

PDA ligation

cystic fibrosis bronchogenic carcinoma
adenocarcinoma
of pancrease

of prostate

carcinoma
of ureter

of prostate

thymoma
ALL
lymphoma
lymphosarcoma
mesothelioma

Hemophagocytic Syndrome
Increased water permeability of nephron
vasopressin

desmopressin

oxytocin

Promote antidiuretic hormone release
nicotine

barbiturates

narcotics

carbamazepine

colchicine

diuretics

isoproterenol

vincristine

vinblastine

amitriptyline

clofibrate

histamine

Inhibit prostaglandin synthesis
salicylates

acetaminophen

NSAIDs

Potentiate ADH action
chloropropamide

cyclophosphamide

tolbutamide

phenformin

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Last modification: May 28, 1998