Central Pontine Myelinolysis (Osmotic Demyelination Syndrome)
⚠️ The physician must carefully balance the risks of persistent hyponatraemia against the dangers of rapid correction.
🎯 High-risk groups: patients with hypoxia, alcoholism, liver disease, or severe malnutrition.
🧠 Central Pontine Myelinolysis (Osmotic Demyelination Syndrome)
- First described in 1956, CPM is characterised by demyelination within the central pons due to rapid electrolyte shifts.
- Most often triggered by overly fast correction of chronic hyponatraemia.
- Despite being non-inflammatory, the syndrome can cause devastating, often irreversible neurological deficits.
⚠️ Aetiology
- Rapid correction of chronic hyponatraemia (especially with hypertonic saline).
- Pathophysiology: as sodium rises quickly, osmotic forces draw water out of swollen CNS cells → dehydration → oligodendrocyte injury and myelin destruction.
- Other causes: severe hypernatraemia correction, liver transplantation, chronic alcoholism, profound malnutrition.
📌 Risk Factors
- Chronic alcohol dependence 🍺
- Malnutrition/cachexia 🍽️
- Liver disease or post–liver transplant 🏥
- Initial sodium <120 mmol/L for >48h ⏳
- Overcorrection: >12 mmol/L in 24h or >18 mmol/L in 48h 🚫
🩺 Clinical Features
- Progressive quadriparesis → quadriplegia.
- Brainstem involvement:
- Dysarthria (slurred speech)
- Dysphagia (difficulty swallowing)
- Ophthalmoplegia with bilateral pinpoint pupils 👁️
- Cognitive/behavioural: delirium, confusion, reduced consciousness.
- Classic exam clue: intact corneal reflexes despite severe deficits.
- Fever may mislead towards infection.
🔍 Differential Diagnosis
- Brainstem stroke 🧠
- Brainstem encephalitis (e.g. Listeria)
- Tetanus or meningitis
- Drug toxicity/overdose
- Seizure-related: post-ictal state, non-convulsive status epilepticus
🧪 Investigations
- Bloods: FBC, U&E, LFTs, clotting; look for chronic liver disease, alcohol misuse, malnutrition.
- CSF: Often non-diagnostic; may show ↑ protein.
- MRI (preferred):
- T2 hyperintense lesion in central pons → classic "bat-wing" or "trident" sign 🦇
- May extend into thalamus, midbrain, medulla or cerebellum.
💊 Management
- Prevention is key ✅:
- Correct sodium slowly: <10–12 mmol/L in 24h, <18 mmol/L in 48h.
- In very high-risk groups (alcoholic, malnourished): aim even lower (≤8 mmol/L per 24h).
- Close monitoring: Frequent serum sodium checks (every 2–4h during correction).
- Supportive therapy:
- Neurorehab, physiotherapy 🏃
- Speech therapy for dysphagia 🗣️
- Nutritional support and alcohol cessation counselling.
- Outcome: Some recovery possible, especially with rehab, but severe cases may leave permanent disability.
📉 Prognosis
- Mild cases: partial recovery possible with rehab.
- Severe cases: persistent locked-in–like state or death.
- Emphasis: slow correction saves lives.
📚 References
- Verbalis JG, et al. (2013). Hyponatremia treatment guidelines 2013. Am J Med.
- Martin RJ. (2004). Central Pontine and Extrapontine Myelinolysis: The osmotic demyelination syndromes. J Neurol Neurosurg Psychiatry.
- NICE CG174: Hyponatraemia Management, 2020 update.
