SIADH

Impaired water excretion due to non-osmotic, unsuppressed ADH release, leading to hypotonic, euvolemic hyponatremia with inappropriately concentrated urine and low serum osmolality. Common causes are malignancy (ectopic production of ADH from lung/brain/pancreatic/GI tumor), medications (SSRI, anti-seizure, chemotherapy, opiates, thiazide diuretics), CNS disease affecting hypothalamus or pituitary gland (meningitis, encephalitis, stroke, head injury, Guillain-Barré syndrome), lung disease (pneumonia, tuberculosis, respiratory failure), and significant stress (major surgery, intense pain, severe nausea).