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) is also called Osmotic Demyelination Syndrome.
Aetiology
- Occurs primarily in individuals undergoing rapid correction of hyponatraemia (low sodium levels).
- As serum sodium rises, water moves out of swollen central nervous system (CNS) cells, leading to demyelination.
Risk Factors
- More common in malnourished individuals, especially alcoholics.
- Also seen in cachexia (severe weight loss) and cancer patients.
- Occurs when initial sodium levels are below 120 mmol/L for more than 48 hours.
- Risk is increased with rapid sodium correction, especially using hypertonic saline solutions.
Clinical Features
- Progressive quadriplegia (paralysis of all four limbs) and brainstem signs.
- Delirium, ophthalmoplegia (paralysis of the eye muscles), bilateral pinpoint pupils.
- Fever, which can complicate diagnosis as it may suggest an infectious cause.
- Corneal reflexes often remain intact.
- Symptoms are directly related to the rate of correction of hyponatraemia.
Differential Diagnosis
- Brainstem encephalitis, brainstem stroke.
- Tetanus, meningitis, drug overdose.
- Post-ictal state, non-convulsive status epilepticus.
Investigations
- FBC, U&E, LFTs, and clotting studies: These may indicate underlying alcohol use or other issues.
- Sodium levels may be below 110 mmol/L, but if hyponatraemia occurred before admission, shifts in sodium levels may not be seen.
- Cerebrospinal fluid (CSF) analysis may show high opening pressure, elevated protein levels, and mild increases in white cell count.
- MRI: Shows demyelination in the pons (central pons, basis pontis, and tegmentum). It may present with a "bat-wing" appearance on T2-weighted MRI sequences. Demyelination may also affect the thalamus, midbrain, medulla, and cerebellum.
Management
- Prevention is key: Correct serum sodium levels slowly, targeting less than 10-12 mmol/L over 24 hours and no more than 18 mmol/L in the first 48 hours, especially in high-risk groups (alcoholics or malnourished patients).
- See hyponatraemia and SIADH (Syndrome of Inappropriate Antidiuretic Hormone Secretion) for more information.
- Some patients may experience long-term recovery following neurorehabilitation.