SIADH
| Headline | |
|---|---|
| Etiology | Ectopic ADH production - small cell lung cancer, leukaemia, lymphoma... Drug induced (see below) Infection Pulmonary: TB, pneumonia CNS: SAH, meningitis, SLE, GBS |
| Epidemiology | |
| Clinical presentation | |
| Pathogenesis | inappropriate ADH secretion (naturally) → too much water resorbed THUS: extracellular water retention; plasma osmolality falls (bloodstream is diluted) THUS: the proximal tubule, trying to compensate, tries to dump water by no longer resorbing as much sodium. THUS: HYPONATREMIA In short, euvolaemic hypo-osmolar hyponatraemia |
| Diagnostic investigations | euvolaemic hyponatraemia low serum osmolality (<275 mOsm/kg) high urine osmolality high urine sodium in the absence of diuretics, hypo/hypervolaemia |
| Management | - Resuscitation: If ↓Na is severe, treat as with any hyponatraemia - Fluid restriction - If severe: Vasopressin receptor antagonist e.g. tolvaptan (contraindicated in severe liver impairment) |
drugs linked to SIADH
- antidepressants: SSRIs, Tricyclic antidepressants
- anticonvulsants e.g. valproate, lamotrigine
- antipsychotics
- some chemotherapy agents
- NSAIDs
- the fun stuff: opioids, MDMA