wiki:endocrine:siadh

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

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

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