Makindo Medical Notes

The physician must weigh the risks of low sodium (Na) levels against the risks of rapid correction. Risk groups include those with hypoxia, alcoholism, or malnutrition.

About Central Pontine Myelinolysis (Osmotic Demyelination Syndrome)

• First described in 1956, Central Pontine Myelinolysis (CPM), also known as Osmotic Demyelination Syndrome, is a condition characterized by the destruction of myelin sheaths within the central pons.
• This demyelination occurs as a result of rapid shifts in electrolyte concentrations, most commonly during correction of hyponatraemia (low sodium levels), leading to irreversible damage to the pons and other regions of the brainstem.

Aetiology

• Primarily caused by rapid correction of chronic hyponatraemia, particularly when sodium levels are corrected too quickly.
• As serum sodium rises, osmotic forces drive water out of previously swollen CNS cells, resulting in dehydration and subsequent demyelination of the pons.
• Other causes include severe hypernatremia correction, liver transplant, chronic alcohol abuse, and malnutrition.

Risk Factors

• More prevalent among malnourished individuals, particularly those with chronic alcoholism.
• Also observed in cachectic (severely underweight) patients, patients with liver disease, and those undergoing liver transplantation.
• Patients are at higher risk if initial serum sodium is under 120 mmol/L for an extended period (e.g., more than 48 hours).
• Risk increases significantly with rapid correction using hypertonic saline solutions, especially if corrected by more than 12 mmol/L over 24 hours.

Clinical Features

• Progressive quadriplegia, initially manifesting as weakness in all four limbs, often progressing to paralysis.
• Brainstem signs, including dysphagia (difficulty swallowing) and dysarthria (difficulty speaking) due to cranial nerve involvement.
• Delirium, mental status changes, and ophthalmoplegia (eye movement abnormalities) with bilateral pinpoint pupils.
• Fever, which can obscure the diagnosis by suggesting an infectious etiology.
• Corneal reflexes typically remain intact despite extensive neurological deficits.
• Symptoms are directly linked to the rate and extent of sodium correction, with faster correction increasing severity.

Differential Diagnosis

• Brainstem Pathologies: Brainstem encephalitis and brainstem strokes, which can present with similar symptoms of quadriparesis and cranial nerve palsies.
• Infectious Causes: Tetanus, meningitis, and drug overdose, which may present with fever, altered mental status, and neurological signs.
• Seizure-Related Conditions: Post-ictal state or non-convulsive status epilepticus, especially if mental status changes and motor deficits are prominent.

Investigations

• Blood Tests:
  • FBC, U&E, LFTs, and clotting studies to assess liver function, potential underlying alcohol use, or malnutrition.
  • Sodium levels may reveal profound hyponatraemia (below 110 mmol/L) if uncorrected; prior shifts in sodium may mask this if correction occurred before testing.
• Cerebrospinal Fluid (CSF) Analysis: May show elevated opening pressure, increased protein, and a mild elevation in white cell count, though CSF is often non-diagnostic in CPM.
• MRI: MRI is the imaging modality of choice, showing demyelination in the pons, particularly in the central pons, basis pontis, and tegmentum. Characteristic "bat-wing" or "trident" appearance may be observed on T2-weighted MRI sequences, with potential extension into the thalamus, midbrain, medulla, and cerebellum.

Management

• Prevention: Slow and controlled correction of serum sodium levels is critical to prevent CPM, targeting less than 10-12 mmol/L increase in the first 24 hours and no more than 18 mmol/L over 48 hours in high-risk patients.
• Monitoring and Support: Patients at risk should undergo close monitoring of serum sodium and neurological status. In severe cases, intensive care support may be required.
• Long-Term Management: Some patients with CPM experience partial recovery over time, especially with neurorehabilitation, though residual deficits often persist.
• Supportive Therapy: Focuses on managing symptoms, including physical therapy for quadriplegia and dysphagia management for swallowing difficulties.