Normovolaemic, normal Na, slightly increased water
Causes of normovolaemic hyponatraemia include:
- SIADH
- tumours
- chest/mediastinum e.g. mesothelioma, thymoma,bronchogenic carcinoma
- nonchest e.g. duodenal carcinoma, pancreatic carcinoma, nasopharyngeal carcinoma, ureteral/prostate carcinoma, uterine carcinoma,leukaemia
- CNS disorders
- mass lesions (tumours, abscesses, subdural hematoma)
- inflammatory diseases (encephalitis, meningitis, multiple sclerosis, systemic lupus, acute intermittent porphyria,)
- degenerative/demyelinative diseases (Guillain-Barré syndrome; spinal cord lesions)
- miscellaneous (head trauma, subarachnoid haemorrhage, acute psychosis, delirium tremens, pituitary stalk section, transphenoidal adenomectomy, hydrocephalus)
- drug induced
- stimulated AVP release (nicotine, phenothiazines, tricyclics)
- direct renal effects and/or potentiation of AVP antidiuretic effects (DDAVP, oxytocin, prostaglandin synthesis inhibitors)
- mixed or uncertain actions (e.g. ACE inhibitors, chlorpropamide, clofibrate, carbamazepine, clozapine, cyclophosphamide, 3,4-methylenedioxymethamphetamine ['Ecstasy'], omeprazole, serotonin reuptake inhibitors, vincristine)
- pulmonary diseases
- infections (tuberculosis, acute bacterial and viral pneumonia, aspergillosis, empyema)
- mechanical/ventilatory (acute respiratory failure, COPD, positive pressure ventilation)
- tumours
- prolonged strenuous exercise (marathon, triathlon, ultramarathon, hot-weather hiking)
- idiopathic
- glucocorticoid deficiency
- hypothyroidism
- water intoxication – primary polydipsia, excess intravenous hypotonic fluids
Reference:
- Adrogué HJ, Tucker BM, Madias NE. Diagnosis and management of hyponatremia: a review. JAMA. 2022 Jul 19;328(3):280-91.
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