Central pontine myelinolysis

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Central pontine myelinolysis
Pons labeled at bottom left
ICD-10	G37.2
DiseasesDB	2198
MedlinePlus	000775
MeSH	D017590

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

Synonyms and keywords: CPM; osmotic demyelination syndrome; osmotic myelinolysis; central pontine myelinosis

Overview

Central pontine myelinolysis is a neurologic disease caused by severe damage of the myelin sheath of nerve cells in the brainstem, more precisely in the area termed the pons. It is a complication of treatment of patients with profound, life threatening hyponatraemia. It occurs as a consequence of a rapid rise in serum tonicity following treatment in individuals with chronic severe hyponatraemia who have made intracellular adaptations to the prevailing hypotonicity. It can also occur as a complication of correcting hypernatremia too rapidly.

Pathophysiology

Brain cells adjust their osmolarities by changing levels of certain osmolytes like Inositol, Betaine, and Glutamine. In hyponatremia the levels of these osmolytes fall, preventing entry of free-water into cells. The reverse is true for hypernatremia. So rapid correction of sodium in hyponatremia would cause the extra cellular fluid to be relatively hypertonic. Free-water would then move out of the cells. This leads to central pontine myelinolysis. Rapid correction of hypernatremia causes water to move into cells, leading to multiple cerebral hemorrhages, equally catastrophic as osmotic demyelination.

Causes

The most common cause is the rapid correction of low blood sodium levels (hyponatremia). Over rapid correction of high levels of salt in the blood (hypernatremia) can also cause the condition.

Risk Factors

It has been postulated that one underlying cause may be the lack of a substance that is essential for brain activity and is lacking due to malnutrition. The fact that this condition is most frequently observed in patients with general ill health (alcoholism, cachexia etc.) is in accordance with this hypothesis.

Natural History, Complications, Prognosis

The nerve damage caused by central pontine myelinolysis is usually long-lasting, and the disorder can cause serious long-term (chronic) disability.

Complications

• Decreased ability to interact with others
• Decreased ability to work or care for self
• Inability to move, other than to blink eyes ("locked in" syndrome)
• Permanent nervous system damage

Diagnosis

Symptoms

• Sudden para or quadraparesis, dysphagia, dysarthria, double vision and loss of consciousness.
• Confusion, delirium
• Balance problems
• Difficulty swallowing
• Hallucinations
• Reduced alertness, drowsiness or sleepiness, lethargy, poor responses
• Speech changes, poor enunciation
• Tremor
• Weakness in the face, arms, or legs, usually affecting both sides of the body
• Locked-in syndrome where cognitive function is intact, but all muscles are paralyzed with the exception of eye blinking

MRI

Imaging by MRI demonstrates an area of high signal return on T2 weighted images.

Treatment

To avoid myelinolysis, the correction of hyponatremia should not exceed 1 mEq/L per hour. There is no specific treatment and the syndrome is associated with high mortality and morbidity. This being a potentially avoidable disaster, following recommendations may be adhered to while maintaining sodium levels:

Hyponatremia

The rate of correction of hyponatremia should be 0.5-1.0meq/L/hr, with not more than a 12 meq/l correction in 24 hrs. If the patient has ongoing seizures (or [Na⁺]<115 meq/li), correction can be attempted at up to 2 meq/L/hr, but only while seizure activity lasts and the [Na⁺] exceeds 125-130 meq/Li.

Hypernatremia

The rate of correction of hypernatremia should be at 0.5meq/L/hr and should not exceed 12 meq/Li/24hrs.