This is a mechanism of disease flowchart for syndrome of inappropriate ADH secretion, including the etiologies, pathophysiology, and manifestations of SIADH.
ADDITIONAL TAGS:
Regulation / feedback
Signs / symptoms
Labs / tests / imaging results
Syndrome of inappropriate antidiuretic hormone secretion
Core concepts
Pulmonary
Paraneoplastic
Pharmacology / toxicity
Microbial pathogenesis
Biochem / molecular bio
Flow gradients
Genetics / hereditary
CNS trauma / inflamm.
Pathophysiology
Etiology
Manifestations
↑ antidiuretic hormone (ADH, vasopressin) production
Signaling cascade in distal convoluted tubule and collecting ducts of nephrons in kidneys
Water drawn out of urine to hyperosmolar kidney tissue
↓ serum osmolality (water retention) → transient volume expansion
↑ ANP, ↑ BNP,
and ↓ aldosterone
↑ urinary sodium → ↑ water excretion
Insertion of additional aquaporin-2 channels (water canals) into luminal cell membrane
↑ urine osmolality / concentration
Euvolemic hyponatremia
No edema
Normotensive
Anorexia
Nausea, vomiting
Headache
Muscle cramps
Muscle weakness
Lethargy
Confusion
Osmotic fluid shifts: cerebral edema and
↑ intracranial pressure
Altered consciousness
Seizures
Mild hyponatremia
Moderate hyponatremia
Severe hyponatremia
(Na 120 mEq/L)
Ectopic / paraneoplastic ADH production
↑ pituitary ADH production
-Anticonvulsants (carbamaze, valproate)
-Antidepressants (SSRIs [sertraline], MAO inhibitors, TCAs [amitriptyline])
-Antineoplastics (mitotic inhibitors [vincristine], alkylating [cyclophosphamide, cisplatin])
-Illicit drugs (MDMA)
-Antipsychotics (haloperidol)
-Analgesics (NSAIDS, opioids)
Infections, like HIV or pneumonias
Chronic obstructive pulmonary disease
Stroke, hemorrhage, iatrogenic
(following neurosurgery), trauma
Vasopressin-2 receptor gene mutation (gain of function → constitutive receptor activation)
Nephrogenic
Small cell lung cancer
Olfactory neuroblastoma
Head / neck cancers
↑ Upwards Arrow 24
↓ Downwards Arrow 25
→ Rightwards Arrow 26
← Leftwards Arrow 27
↔ Left-Right Arrow 29
↕ Up-Down Arrow 18
