- Carcinomas: Lung, Duodenum, Pancreas, Ovary, Bladder, ureter
- Head trauma (closed and penetrating)
- Infections: Pneumonia, bacterial or viral, Abscess, lung or brain, Tuberculosis, lung or brain, Meningitis, bacterial or viral, AIDS
- Vascular: CVA (SAH)
- Neurologic: Guillain - Barre- syndrome, Multiple sclerosis
- Metabolic: Acute intermittent porphyrias
- Drugs (MCQ):
- Vasopressin or desmopressin,
- Tricyclic antidepressants,
- Serotonin reuptake inhibitor
Clinical features of SIADH
They are due to hyponatremia which are related to osmotic water shift. It lead to increase intra cellular fluid volume in the brain cell causing swelling of the brain cell which lead to cerebral edema. Patient may be asymptomatic, or may have convulsion (LQ 2012), Coma or death.
Laboratory features of SIADH
- Hyponatremia (serum sodium < 135 mEq/L)
- Inappropriately elevated urine osmolality (> 100 mosm/kg)
- Decreased serum osmolality (< 280 mosm/kg)
- B.U.N. and serum uric acid tends to fall because of plasma dilution and increased excretion of nitrogenous products.
- Serum potassium and Bicarbonate levels are normal in SIADH.
- Increase urinary sodium (More than 30 meq/lil
- Water loading test is done
Extra Edge Water loading test
In SIADH there is an abnormal water load test (i.e. inability to excrete at least 90% of a 20 ml/kg water load in 4 h and/or failure to dilute urine osmolality <100 mosm/kg), and there is plasma ADH levels inappropriately elevated relative to plasma osmolality.