Central pontine myelinolysis overview

# Overview
The most common cause of central pontine myelinolysis is a rapid correction(>48-hours duration) of hyponatremia in patients with the history of prolonged hyponatremia. Other causes of central pontine myelinolysis may include: Lengthened orthotopic liver transplantation, hypophosphatemia secondary to refeeding syndrome, deficiencies in neuronal/glial cell energy supply and utilization which produce glial cell apoptosis and thus the clinical syndrome of central pontine myelinolysis and prolonged ischemia. The most potent risk factor in the development of central pontine myelinolysis is hyponatremia. Other risk factors include: Liver dysfunction and liver diseases, hypocholesterolemia, alcoholism, malnutrition, systemic medical disease and hemodialysis. Brain MRI is the gold standard test for the diagnosis of central pontine myelinolysis. The following findings on performing Brain MRI are confirmatory for central pontine myelinolysis: T2 hyperintensity in the central pontine region in the axial plane and hyperintense lesion in the midpons in the midsagittal T2-weighted MRI. Treatment of patients with central pontine myelinolysis is mainly supportive because once the osmotic demyelination has begun, there is no cure or specific treatment. Alcoholic patients should receive vitamin supplementation including vitamin B6, B9 and B12 and evaluation of their nutritional status.

# Historical Perspective
Central pontine myelinolysis was first discovered by Raymond Delacy Adams, an an American neurologist, in 1959. Raymond Delacy Adams and colleagues observed a rapidly evolving quadriplegia and pseudobulbar palsy in a young alcoholic man whose postmortem examination showed a large, symmetrical, essentially demyelinative lesion occupying the greater part of the base of the pons In 1950.

# Pathophysiology
It is understood that central pontine myelinolysis is caused by the rapid correction of hyponatremia. The CNS is particularly susceptible to reductions in plasma osmolarity, specially during hyponatremia which is the most commonly encountered electrolyte disturbance. When a decrease in the plasma osmolarity happens, neural cells first swell but then they are able to regain their original volume through the release of inorganic and organic osmolytes and exit of osmotically obligated water. Subsequent exposure to hypertonic stress(e.g., correction of hyponatremia with hypertonic I.V. solutions)resulting from a rapid correction of hyponatremia causes the ions to quickly re-enter the intracellular space and compels the water to follow. If the serum sodium levels rise too rapidly, the increased extracellular tonicity will continue to drive water out of the brain's cells because the brain cells do not have enough time to bring extracellular sodium into the cell, so the water goes out very fast. This can lead to cellular dysfunction and central pontine myelinolysis and finally death.

# Causes
The most common cause of central pontine myelinolysis is rapid correction(>48-hours duration) of hyponatremia in patients with the history of prolonged hyponatremia. Other causes of central pontine myelinolysis may include: Lengthened orthotopic liver transplantation, hypophosphatemia secondary to refeeding syndrome, deficiencies in neuronal/glial cell energy supply and utilization which produce glial cell apoptosis and thus the clinical syndrome of central pontine myelinolysis and prolonged ischemia.

# Differentiating central pontine myelinolysis from Other Diseases
On the basis central pontine myelinolysis must be differentiated diseases that cause acute confusion, lethargy, speech difficulties and bilateral weakness or quadriplegia such as: Posterior leukoencephalopathy syndrome, infective encephalitis, ischemic Brain stem infarction, thalamus infarction due thrombosis of the basilar artery, diffuse hypoxic encephalopathy, metastasis to the brain and brain tumors such as glioma.

# Epidemiology and Demographics
The prevalence of central pontine myelinolysis is approximately 250500 per 100,000 in the general population. Among hospitalized patients in the ICU the incidence of central pontine myelinolysis is approximately 2500 per 100,000 patients. Among patients undergoing liver transplantation the incidence of central pontine myelinolysis is approximately 10,000 per 100,000 patients. The case-mortality rate of central pontine myelinolysis is approximately 12%. Patients of all age groups may develop central pontine myelinolysis but the incidence of central pontine myelinolysis increases with age. There is no racial predilection to central pontine myelinolysis. Central pontine myelinolysis affects men and women equally. There is no regional predilection to central pontine myelinolysis.

# Risk Factors
The most potent risk factor in the development of central pontine myelinolysis is hyponatremia. Other risk factors include: Liver dysfunction and liver diseases, hypocholesterolemia, alcoholism, malnutrition, systemic medical disease and hemodialysis.

# Natural History, Complications, and Prognosis
The symptoms of central pontine myelinolysis typically develop immediately after injury to the neurons of the brain stem. Patients, with Central Pontine Myelinolysis, may develop permanent neurological damages. Common complications of central pontine myelinolysis include: Locked-in syndrome, quadriparesis, ataxia, acute Psychosis, pseudobulbar palsy, parkinson's disease symptoms, dystonia, pneumonia, coma and death. The mortality of patients with central pontine myelinolysis is approximately 8% in the acute setting. Approximately 65% of patients with central pontine myelinolysis may achieve a good or moderate outcome (no functional deficit or independence despite minor deficits). Depending on the time of the diagnosis, the prognosis may vary and the disease may be potentially reversible when therapeutic interventions are initiated rapidly.

# Diagnosis

## Diagnostic Study of Choice
Brain MRI is the gold standard test for the diagnosis of central pontine myelinolysis. The following findings on performing Brain MRI are confirmatory for central pontine myelinolysis: T2 hyperintensity in the central pontine region in the axial plane and hyperintense lesion in the midpons in the midsagittal T2-weighted MRI.

## History and Symptoms
Patients with central pontine myelinolysis may have a positive history of: Malnutrition, alcohol use disorder, chronic liver disease, hyperemesis gravidarum, hypophosphatemia secondary to refeeding syndrome and prolonged ischemia. These patients with central pontine myelinolysis most commonly have a history of rapid sodium correction, greater than 0.5-1.0 mEq/L per hour. The most susceptible patients are those with: Chronic hyponatremia (>48 hours), severe hyponatremia (Na <120 mEq/L) and both chronic hyponatremia and severe hyponatremia. Common symptoms of central pontine myelinolysis include: Spastic quadriparesis, dysarthria, pseudobulbar palsy and altered mental status. In some patients, parkinsonian features, behavioral manifestations, and neuropsychological symptoms can also be present: Personality changes, labile affect, disinhibition, poor judgment, paranoid delusions, emotional lability, delirium, hallucinations and catatonia.

## Laboratory Findings
Laboratory finding consistent with the diagnosis of central pontine myelinolysis is hypoosmotic hyponatremia and the rapid correction of hyponatremia is the cause of central pontine myelinolysis.

## CT scan
Brain CT scan may be helpful in the diagnosis of central pontine myelinolysis. Findings on CT scan suggestive of central pontine myelinolysis include: A symmetric, centrally located region of low attenuation within the pons and symmetric low-attenuation foci within the lateral thalami.

## MRI
Brain and spinal cord MRIs may be helpful in the diagnosis of Central pontine myelinolysis. Findings on MRI diagnostic of Central pontine myelinolysis include: Symmetric signal intensity abnormality in the central pons at T2-weighted and FLAIR imaging which may progress to classic hyperintense trident-shaped central pontine abnormality, with sparing of the ventrolateral pons and corticospinal tracts, decreased T1 signal intensity, fluid attenuated inversion recovery (FLAIR) hyperintense lesion in the pons and intramedullary central T2 hyperintensity at axial T2W of spinal cord and sagittal T2W of thoracic spinal cord.

# Treatment

## Medical Therapy
Treatment of patients with central pontine myelinolysis is mainly supportive because once the osmotic demyelination has begun, there is no cure or specific treatment. Alcoholic patients should receive vitamin supplementation including vitamin B6, B9 and B12 and evaluation of their nutritional status.

## Primary Prevention
To minimize the risk of central pontine myelinolysis developing from its most common cause, overly rapid reversal of hyponatremia, the hyponatremia should be corrected slowly. The primary goals of treating hypernatremia are estimating the magnitude of water deficit, determining the proper rate of correction, addressing the concurrent electrolyte or volume deficits and calculating the fluid deficit regimen using the estimated water deficit and desired rate of correction. Correcting sodium level is vital in order to prevent any permanent brain damage.