CAUSES :
1. Drugs (vincristine, narcotics, thiazide diuretics, cyclophosphamide, carbamazepine, barbiturates, morphine, chlorpropamide, nicotine, beta-adrenergic agents, general anesthetics, oxytocin, bromocriptine)
2. Neoplasms
. Ectopic ADH production
. Oat cell carcinoma of the lung
. Hodgkin disease
. Pancreatic carcinoma
. Bronchogenic carcinoma
3. Infectious diseases
. Meningitis
. Pneumonia
. Pulmonary tuberculosis
. Rocky Mountain spotted fever
. HIV
4. Miscellaneous cardiopulmonary conditions
. Asthma
. Atelectasis
. Myocardial infarction
. Positive-pressure breathing
. Vascular diseases
5. Other
. Chronic pain
. Multiple sclerosis
. Guillain-Barre syndrome
. Lupus erythematosus
. Porphyria
. Hypothyroidism, myxedema
. Idiopathic
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DIFFERENTIAL DIAGNOSIS
1. Postoperative:
. caused by non-osmotic release of ADH
. affects women more than men
. ADH increased by pain and narcotics
2. Postprostatectomy syndrome:
. irrigating solution must be non-conducting (i.e., electrolyte free)
. D5W absorbed
3. Psychotic polydipsia:
. active therapy rarely needed
. diuresis occurs when intake stopped
. intake usually over 10 L/day
. interaction with other psychotropic drugs
4. Acute (usually in children):
. swallowing water during swimming
. diluted formula
. tap water enemas
5. Drug induced:
. oxytocin infusion - given in D5W during labor (oxytocin has antidiuretic effect)
. cyclophosphamide - usually with IV administration
. chlorpropamide (oral hypoglycemic agent)
. carbamazepine - central ADH release
. vincristine - central SIADH
. non-steroidal anti-infl ammatory drugs (NSAIDs)
- decreased renal prostaglandins
6. Diuretic drug induced:
. usually thiazide
. vasopressin increased by decreasing EABV
. usually elderly patients or in bulimia
. correct slowly
7. Tumor induced
. bronchogenic carcinoma (secretes ADH-like substance)
. unexplained persistent hyponatremia may indicate a tumor
8. Pulmonary:
. tuberculosis - secretes ADH
. mechanical ventilation - increased intrathoracic pressure, decreased cardiac output, causes decreased EABV, causes increased ADH
. asthma, acute respiratory failure, pneumonia
9. CNS/hypothalamic irritation:
. meningitis
. Rocky Mountain spotted fever
. encephalitis
. trauma - especially after CNS surgery
10. Endocrine:
. Addison disease
. hypothyroidism
11. Factitious hyponatremia
. caused by increased serum glucose, cholesterol or proteins
12. Other:
. Appropriate ADH secretion and hyponatremia with decreased effective arterial blood volume, e.g., congestive heart failure, nephrotic syndrome, cirrhosis
LABORATORY
β’ BUN low or normal
β’ Creatinine low or normal
β’ Urine osmolality 200+ mOsm/kg
β’ Urinary Na concentration > 20 mEq/L (> 20 mmol/L)
β’ Elevated serum concentration ADH
β’ Normal adrenal and renal function
β’ Uric acid low
SPECIAL TESTS Oral water-loading test may be helpful in diagnosis in some patients. Response to water-load will be impaired in SIADH. May be unsafe
and often not necessary to establish diagnosis