SIADH
(Syndrome of Inappropriate ADH secretion)
- Most common = secondary to other disease process.
- Hereditary SIADH, (nephrogenic SIADH) - mutation in vasopressin 2 (V2) receptors in the kidneys
- variously caused by excessive Vasopressin (exogenous or ectopic) or increased sensitivity to Vasopressin as well as unknown mechanisms.
| Secondary causes of SIADH | |
|---|---|
| Respiratory | • pneumonia commonly causes SIADH by unknown mechanism • asthma, atelectasis and pneumothorax |
| CNS | • any CNS condition including stroke, malignancy, psychosis, infection • trauma |
| Malignancy | • Small cell CA lung is the most common malig causing ectopic ADH production • GIT and other malignancies are also associated with SIADH |
| Endocrine | • hypopituitarism and hypothyroidism |
| Surgery | • not uncommon after surgery. Possibly pain mediated mechanism |
| Drugs | • Most common: carbamazepine, oxcarbazepine, chlorpropamide, cyclophosphamide & SSRIs. |
| Other | • almost any other condition - HIV, automimmune diseases and inflammatory processes |
Bartter and Schwartz criteria for SIADH:
- various versions which include different lab values, but essential elements:
- Hyponatremia with hypo-osmolality
- Continued renal excretion of sodium
- Urine less than maximally dilute
- Absence of clinical evidence of volume depletion
- Correction of hyponatremia by fluid restriction
Manifestation
- hyponatraemia and hypo-osmolality
- may be asymptomatic depending on chronicity of development and causative background
- severe cases:
- Confusion, disorientation, delirium
- Generalized muscle weakness, myoclonus, tremor, asterixis
- hypo-reflexia, ataxia, dysarthria
- Cheyne-Stokes respiration, pathologic reflexes
- Generalized seizures, coma
Management
- depends on acuity of presentation
- asymptomatic patients can usually be assumed to be chronic development and Mx includes fluid (water) restriction and diuretics. V2 antagonists occasionally
- when development is acute and patient unwell, rate of correction of osmolality is critical
- generally accepted, in most settings, correction of seNa+ at rate ≤1mmol/hr to avoid Central Pontine Myelinolysis
- hypertonic saline - usually 3%
- water restriction
- diuretics and V2 antagonists