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# Osmotic demyelination syndrome (central pontine myelinolysis)

Brain damage, mainly in the pons, caused by correcting low blood sodium too fast. It can cause paralysis or locked-in syndrome and is largely preventable.

Updated 2026-11-01

## Structures involved

Tap one to see what it is and open it in 3D.

- [Pons](https://durgical.com/en/anatomy/pons/)
- [Midbrain](https://durgical.com/en/anatomy/midbrain/)
- [Medulla oblongata](https://durgical.com/en/anatomy/medulla-oblongata/)
- [Thalamus](https://durgical.com/en/anatomy/thalamus/)
- [Caudate nucleus](https://durgical.com/en/anatomy/caudate-nucleus/)
- [Putamen](https://durgical.com/en/anatomy/putamen/)
- [White matter](https://durgical.com/en/anatomy/white-matter-of-telencephalon/)

## Why it happens

- [Osmosis, osmolarity and tonicity](https://durgical.com/en/physiology/osmosis-osmolarity-and-tonicity/)
- [Cell volume regulation](https://durgical.com/en/physiology/cell-volume-regulation/)
- [Reasoning through fluid and electrolyte imbalances](https://durgical.com/en/physiology/reasoning-through-fluid-and-electrolyte-imbalances/)
- [Glial cells: astrocytes, oligodendrocytes, microglia, Schwann cells](https://durgical.com/en/histology/glial-cells-astrocytes-oligodendrocytes-microglia-schwann-cells/)

## What it is

Acute demyelination of the central pons, and sometimes other brain areas (extrapontine myelinolysis), that follows a rapid rise in serum sodium, most often during over-rapid correction of chronic hyponatraemia.

## Who gets it

Uncommon but high-yield because it is largely iatrogenic and preventable. It is seen in hospitalised patients with chronic hyponatraemia, especially those with alcohol use disorder, malnutrition or liver disease, and after liver transplantation.

## Causes

- Rapid correction of chronic hyponatraemia (present for more than 48 hours)
- Rapid rises in sodium from hypertonic saline, unrecognised water diuresis or stopping a cause of SIADH
- Less often, rapid sodium shifts in patients without hyponatraemia

## Risk factors

- Serum sodium at or below about 105 mmol/L
- Alcohol use disorder
- Malnutrition, including anorexia nervosa and refeeding
- Hypokalaemia
- Advanced liver disease and liver transplantation
- Prolonged vomiting, including hyperemesis gravidarum, and thiazide use

## Pathophysiology

In chronic hyponatraemia, brain cells lose organic osmolytes to avoid swelling. When sodium rises too fast, water leaves the cells before osmolytes can be rebuilt, causing shrinkage and injury of oligodendrocytes, breakdown of the blood-brain barrier and loss of myelin. The central pons is especially vulnerable because of its dense mix of grey and [white matter](https://durgical.com/en/anatomy/white-matter-of-telencephalon/). Symptoms typically appear two to six days after correction, often after an initial improvement.

## Classification

- Central pontine myelinolysis
- Extrapontine myelinolysis (basal ganglia, [thalamus](https://durgical.com/en/anatomy/thalamus/), [cerebellum](https://durgical.com/en/anatomy/anterior-quadrangular-lobule/), cerebral white matter)
- Combined pontine and extrapontine forms

## Symptoms and signs

- A biphasic course: initial improvement of hyponatraemic encephalopathy, then neurological worsening days later
- Dysarthria and dysphagia (pseudobulbar palsy)
- Weakness of all four limbs (quadriparesis), initially flaccid, later spastic
- Confusion, drowsiness and behavioural changes
- Movement disorders such as tremor, dystonia or parkinsonism in extrapontine forms
- Locked-in syndrome in severe cases: awake but able to move only the eyes

## Red flags

- A rise in sodium above recommended correction limits in the first 24 or 48 hours
- New dysarthria, dysphagia or limb weakness days after sodium correction
- Reduced level of consciousness or inability to protect the airway
- Large urine output (water diuresis) during treatment of hyponatraemia

## Diagnosis

**Clinical**
Suspected from the timeline: new brainstem or extrapontine signs two to six days after a rapid rise in sodium in a patient with risk factors.

**Tests**
Review of serial sodium values to document the rate of correction; electrolytes including potassium, phosphate and magnesium; [liver](https://durgical.com/en/anatomy/liver/) function and nutritional assessment. Brainstem auditory evoked responses may support pontine involvement.

**Imaging**
MRI is the imaging test of choice: T2/FLAIR hyperintensity in the central [pons](https://durgical.com/en/anatomy/pons/) (often trident or bat-wing shaped), sparing the periphery, and diffusion-weighted changes that may appear earlier; MRI can be normal in the first days and should be repeated. CT is insensitive.

## Differential diagnosis

- [Basilar artery](https://durgical.com/en/anatomy/basilar-artery/) thrombosis and pontine stroke
- Wernicke encephalopathy
- Brainstem tumour or encephalitis
- Multiple sclerosis or acute disseminated encephalomyelitis
- Hepatic encephalopathy

## Goal of treatment

Prevention through controlled correction of chronic hyponatraemia; once established, supportive care, airway protection and rehabilitation.

## Treatment

**Follow-up**
Prevention: in chronic hyponatraemia, sodium is corrected slowly within limits set by guidelines, with frequent sodium checks (every few hours), strict fluid balance and urine output monitoring, and extra caution in high-risk patients.

**Acute**
If overcorrection occurs, re-lowering of sodium with hypotonic fluids and desmopressin under specialist supervision may limit injury.

**Conservative**
Supportive care in hospital, often in intensive care: airway protection, nutrition (sometimes by tube), prevention of aspiration, pressure injuries and thrombosis.

**Rehabilitation**
Long-term physiotherapy, speech and swallowing therapy and occupational therapy.

## Complications

- Locked-in syndrome
- Permanent quadriparesis or spasticity
- Aspiration pneumonia from dysphagia
- Respiratory failure
- Chronic movement disorders and cognitive impairment
- Death

## Prognosis

Outcomes vary widely: some patients recover substantially over months, while others remain severely disabled or die. Prognosis cannot be judged from early MRI findings, and recovery may continue for a long time with supportive care.

## Prevention

- Gradual correction of chronic hyponatraemia within guideline limits
- Frequent sodium monitoring and anticipation of water diuresis
- Correction of hypokalaemia with attention to its effect on sodium
- Special care in alcohol use disorder, malnutrition and liver disease

## Test yourself

Think of the answer, then tap the question to see it.

## What is the most common cause of osmotic demyelination syndrome?

Over-rapid correction of chronic hyponatraemia.

## When do symptoms typically appear after sodium correction?

Two to six days later, often after an initial improvement (biphasic course).

## What is the most severe clinical picture of central pontine myelinolysis?

Locked-in syndrome: quadriplegia and anarthria with preserved consciousness and vertical eye movements.

## Which imaging test confirms the diagnosis?

MRI, showing T2/FLAIR hyperintensity in the central pons; it may be normal early and need repeating.

## Which patient groups are at high risk?

Patients with alcohol use disorder, malnutrition, hypokalaemia, liver disease or liver transplantation.

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## Related conditions

- [Hyponatraemia](https://durgical.com/en/conditions/hyponatraemia/)
- [Syndrome of inappropriate antidiuretic hormone secretion (SIADH)](https://durgical.com/en/conditions/syndrome-of-inappropriate-antidiuretic-hormone-secretion/)
- [Alcohol use disorder](https://durgical.com/en/conditions/alcohol-use-disorder/)
- [Cirrhosis](https://durgical.com/en/conditions/cirrhosis/)
- [Wernicke encephalopathy (thiamine deficiency)](https://durgical.com/en/conditions/wernicke-encephalopathy/)
- [Hypokalaemia](https://durgical.com/en/conditions/hypokalaemia/)
- [Refeeding syndrome](https://durgical.com/en/conditions/refeeding-syndrome/)
- [Brainstem stroke syndromes (Wallenberg and others)](https://durgical.com/en/conditions/brainstem-stroke-syndromes/)
- [Hyperemesis gravidarum](https://durgical.com/en/conditions/hyperemesis-gravidarum/)
- [Anorexia nervosa](https://durgical.com/en/conditions/anorexia-nervosa/)

Educational information, not medical advice. For any symptom, see a health professional.

Sources: [Osmotic demyelination syndrome: MedlinePlus Medical Encyclopedia](https://medlineplus.gov/ency/article/000775.htm) (MedlinePlus (U.S. National Library of Medicine), 2025).

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Source: https://durgical.com/en/conditions/osmotic-demyelination-syndrome/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/conditions/osmotic-demyelination-syndrome/