Central pontine myelinosis

Infobox_Disease
Name = Central pontine myelinosis


Caption =
DiseasesDB = 2198
ICD10 = ICD10|G|37|2|g|35
ICD9 = ICD9|341.8
ICDO =
OMIM =
MedlinePlus = 000775
eMedicineSubj = neuro
eMedicineTopic = 50
MeshID = D017590

Central pontine myelinolysis or osmotic demyelination syndrome is a demyelinating lesion in the brain that occurs with rapid correction of hyponatremia (low sodium levels in the blood). It is characterized by acute paralysis, dysphagia (difficulty swallowing), and dysarthria (diffuculty speaking), and other neurological symptoms.

It is most common in patients with chronic hyponatremia, which is usually caused by alcoholism. The prognosis is poor.

Central pontine myelinolysis is a complication of treatment of patients with profound, life-threatening hyponatraemia (low sodium). 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. Individuals with hyponatremia should receive no more than 8-10mmol of sodium per day to prevent central pontine myelinosis.

Pathology

The currently accepted theory states that the brain cells adjust their osmolarities by changing levels of certain osmolytes like Inositol, Betaine, Glutamine etc. 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 a central pontine myelinolysis, manifesting as the paralyses.

The demyelination of the axons (nerve fibers in the brain) damages them.cite journal
author=Medana IM, Esiri MM
title=Axonal da

journal=Brain
volume=126
issue=Pt 3
pages=515–30
year=2003
month=March
pmid=12566274
doi=
url=http://brain.oxfordjournals.org/cgi/pmidlookup?view=long&pmid=12566274
issn=]

In the context of chronic low plasma sodium, the brain's cells (neurons and glia) adapt by taking in a small amount of water; the net effect is to move water out of the interstium and equilibrate (or nearly so) the intracellular and extracellular tonicities. The chronic hyponatremia is thus compensated.

With correction of the hyponatremia with intravenous fluids, the intra- and extra-cellular tonicities are again changed, this time in the opposite direction. With the use of intravenous hypertonic saline, the correction can be too quick, not allowing enough time for the brain's cells to adjust to the new tonicity. With a rise in extracellular tonicity, the cells compensate by losing a small amount of water. This loss will continue until the intra- and extra-cellular tonicities are equal. If hypertonic therapy continues or is too rapid, the extracellular tonicity will continue to drive water out of the brain's cells, leading to cellular dysfunction and the condition of central pontine myelinolysis.

Rapid correction of hypernatremia causes water to move into cells, leading to multiple cerebral hemorrhages, equally catastrophic as osmotic demyelination.

Prevention

This being a potentially avoidable disaster, following recommendations may be adhered to while maintaining sodium levels:

* "Hyponatremia:" Correction rate=0.5-1.0meq/L/hr, with not more than 12meq/l correction in 24 hrs. If the patient has seizures (or [Na⁺] <115), correction can be attempted at up to 2meq/L/hr, but only till seizure activity lasts and [Na⁺] reaches above 125-130 meq/L.

* "Hypernatremia:" Correct at 0.5meq/L/hr. Not more than 12 meq/L/24hrs.

Management

Once demyelination has begun, there is no specific treatment. Care is supportive, with the goal of preventing complications like aspiration pneumonia or deep vein thrombosis. Alcoholics are usually given vitamins to correct for other deficiencies.

Research has lead to improved outcomes.cite journal
author=Brown WD
title=Osmotic demyelination disorders: central pontine and extrapontine myelinolysis
journal=Curr. Opin. Neurol.
volume=13
issue=6
pages=691–7
year=2000
month=December
pmid=11148672
doi=
url=http://meta.wkhealth.com/pt/pt-core/template-journal/lwwgateway/media/landingpage.htm?issn=1350-7540&volume=13&issue=6&spage=691
issn=] Animal studies suggest inositol reduces the severity of osmotic demyelination syndrome if given prior to rapid correction of chronic hyponatraemia. [cite journal
author= Silver SM, Schroeder BM, Sterns RH, Rojiani AM
title= Myoinositol administration improves survival and reduces myelinolysis after rapid correction of chronic hyponatremia in rats
journal= J Neuropathol Exp Neurol
year= 2006
volume= 65
issue= 1
pages= 37-44
id=PMID 16410747] Further study is required prior to its application in humans for this indication.

Prognosis

The prognosis is overall poor. Some patients die. Most survive, however, and of the survivors, approximately one-third recover; one-third are disabled but are able to live independently; one-third are severely disabled.cite journal
author=Abbott R, Silber E, Felber J, Ekpo E
title=Osmotic demyelination syndrome
journal=BMJ
volume=331
issue=7520
pages=829–30
year=2005
month=October
pmid=16210283
pmc=1246086
doi=10.1136/bmj.331.7520.829
url=
issn=] Permanent disabilities range from minor tremors and ataxia to signs of severe brain damage, such as spastic quadriparesis and locked-in syndrome. [http://www.emedicine.com/NEURO/topic50.htm] Some improvements may be seen over the course of the first several months after the condition stabilizes.

The extent of recovery depends on how many axons were damaged.

References