Osmotic demyelination syndrome

Central pontine myelinolysis
Synonyms	Osmotic demyelination syndrome, central pontine demyelination
Axial fat-saturated T2-weighted image showing hyperintensity in the pons with sparing of the peripheral fibers, the patient was an alcoholic admitted with a serum Na of 101 treated with hypertonic saline, he was left with quadreparesis, dysarthria, and altered mental status
Specialty	neurology
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Classification	· ·

Central pontine myelinolysis (CPM) is a neurological disorder caused by severe damage of the myelin sheath of nerve cells in the area of the brainstem termed the pons, predominately of iatrogenic, treatment-induced cause. It is characterized by acute paralysis, dysphagia (difficulty swallowing), and dysarthria (difficulty speaking), and other neurological symptoms.

Central pontine myelinolysis was first described by Adams et al in 1959 as a clinicopathological entity. The original paper described four cases with fatal outcomes, and the findings on autopsy. The cause was not known then but the authors suspected either a toxin or a nutritional deficiency. ‘Central pontine’ indicated the site of the lesion and ‘myelinolysis’ was used to emphasise that myelin was affected preferentially compared to the other neuronal elements. The authors intentionally avoided the term ‘demyelination’ to describe the condition, in order to differentiate this condition from multiple sclerosis and other neuroinflammatory disorders.

Since this original description, demyelination in other areas of the central nervous system associated with osmotic stress has been described outside the pons. The more general term "osmotic demyelination syndrome" is now preferred to the original more restrictive term "central pontine myelinolysis".

Central pontine myelinolysis presents most commonly as a complication of treatment of patients with profound hyponatremia (low sodium), which can result from a varied spectrum of conditions, based on different mechanisms. It occurs as a consequence of a rapid rise in serum tonicity following treatment in individuals with chronic, severe hyponatremia who have made intracellular adaptations to the prevailing hypotonicity.

Clinical presentation of CPM is heterogeneous and depend on the regions of the brain involved. Prior to its onset, patients may present with the neurological signs and symptoms of hyponatraemic encephalopathy such as nausea and vomiting, confusion, headache and seizures. These symptoms may resolve with normalisation of the serum sodium concentration. Three to five days later, a second phase of neurological manifestations occurs correlating with the onset of myelinolysis. Observable immediate precursors may include seizures, disturbed consciousness, gait changes, and decrease or cessation of respiratory function.

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