Osmotic demyelination syndrome

Background

• Formerly called "central pontine myelinolysis"
• A neurologic condition caused by rapid correction of hyponatremia, with starting serum sodium normally 120 meq/L or less
• Caused by rapid correction of hyponatremia (>12 mEq/L/24 h), as water moves from cells to extracellular fluid, yielding intracellular dehydration.
• Symptoms are often irreversible or only partially reversible

Risk Factors

• Chronic heart failure
• Alcoholism
• Cirrhosis
• Hypokalemia
• Malnutrition
• Treatment with vasopressin antagonists (e.g. tolvaptan)

Risk Factors for Over-correction

• Lower initial sodium
• Schizophrenia
• Lower baseline urine sodium

Clinical Features

Symptoms can be present 2-6 days after rapid correction of serum sodium

• Dysarthria
• Dysphagia
• Lethargy
• Behavioral disturbances/ confusion
• Paraparesis or quadriparesis
• Seizures
• "Locked in" syndrome
• Coma and death

Differential Diagnosis

Altered mental status

Diffuse brain dysfunction

• Hypoxic encephalopathy
• Acute toxic-metabolic encephalopathy (Delirium)
  • Hypoglycemia
  • Hyperosmolar state (e.g., hyperglycemia)
  • Electrolyte Abnormalities (hypernatremia or hyponatremia, hypercalcemia)
  • Organ system failure
  • Hepatic Encephalopathy
  • Uremia/Renal Failure
  • Endocrine (Addison's disease, Cushing syndrome, hypothyroidism, myxedema coma, thyroid storm)
  • Hypoxia
  • CO2 narcosis
• Hypertensive Encephalopathy
• Toxins
• TTP / Thrombotic thrombocytopenic purpura
• Alcohol withdrawal
• Drug reactions (NMS, Serotonin Syndrome)
• Environmental causes
  • Hypothermia
  • Hyperthermia
• Deficiency state
  • Wernicke encephalopathy
  • Subacute Combined Degeneration of Spinal Cord (B12 deficiency)
  • Vitamin D Deficiency
  • Zinc Deficiency
• Sepsis
• Osmotic demyelination syndrome (central pontine myelinolysis)
• Limbic encephalitis

Primary CNS disease or trauma

• Direct CNS trauma
  • Diffuse axonal injury
  • Subdural/epidural hematoma
• Vascular disease
  • Intraparenchymal hemorrhage
• SAH
• Stroke
  • Hemispheric, brainstem
• CNS infections
  • Encephalitis
  • Anti-NMDA receptor encephalitis
  • Meningitis
• Neoplasms
  • Paraneoplastic Limbic encephalitis
  • Malignant Meningitis
  • Pancreatic Insulinoma
• Seizures
  • Nonconvulsive status epilepticus
  • Postictal state
• Dementia
  • Alzheimer's
  • Lewy Body Dementia
  • Frontotemporal Dementia

Psychiatric

• Acute psychosis
• Catatonia
• Excited delirium
• Malingering
• Steroid induced psychosis

Evaluation

• Evaluate for alternative/reversible causes of AMS or exacerbating factors
• MRI can be used to visualize the pontine lesion, with a characteristic "batwing" lesion of the pons appearing in typical cases

Management

• Desmopressin at 2 mcg q6 hrs IV/SC
• 6 mL/kg of 5% dextrose in water, repeated until serum sodium rise back below 9 mEq in 24 hrs
• If concerns for iatrogenic rapid increase in serum Na concentration (IV crystalloid bolus before Na lab comes back):
  • Stop IV fluids, send urine osmolality, repeat serum Na
  • If uOsm is < 100 mOsm/L, this suggests free water diuresis
  • Or if sodium appears to be on a trajectory to increase >8mEq/L in 24hrs
  • Administer DDAVP 1 mcg x1

Disposition

• Admit

Prevention

See hyponatremia for safe correction rate

See Also

• Hyponatremia
• Hypernatremia