Central pontine myelinolysis (CPM), also referred to as osmotic demyelination syndrome, is a demyelinating disease that is caused by significant damage to the myelin sheath of nerve cells in the middle of the brainstem, specifically the pons region.
The clinical presentation of central pontine myelinolysis is variable. Patients may be asymptomatic, or have mild to severe symptoms, including rapid onset of pseudobulbar symptoms (e.g., difficulty swallowing or speaking), paraparesis, quadriparesis, confusion, psychiatric symptoms (e.g., delirium or hallucinations), "locked-in syndrome," in which there is paralysis of the lower limb musculature and cranial nerves resulting in a lack of expressive communication ability, although the intellectual activity is unaffected .
The symptoms may appear with a biphasic course, consisting of seizures and/or encephalopathy, with a period of improvement, followed by deterioration consisting of spastic quadriplegia, dysarthria, dysphagia, and occasionally oculomotor abnormalities such as horizontal gaze paralysis .
Workup of central pontine myelinolysis consists of a history, physical exam, laboratory testing, and imaging. Patients with a history of rapid correction of severe hyponatremia (plasma serum level <120 mq/L persisting for two or more days, that has been corrected at a rate greater than 8 mq/L in 48 hours), patients with liver disease or alcohol abuse should be considered at high-risk for central pontine myelinolysis  . During the neurologic exam, the clinician should assess signs of confusion, occulomotor dysfunction (e.g., horizontal gaze paralysis), impaired speech or swallowing, and signs of spastic quadriplegia such as limb weakness, increased tonicity of the limb muscles, and hyperreflexia). The primary laboratory test consists of a chemistry panel (sodium, potassium, chloride, bicarbonate, glucose, creatine, and BUN). Liver function test can also be performed when clinically indicated.
Computed tomography (CT) and magnetic resonance imaging (MRI) have been used to aid in the diagnosis    . Imaging test results may be normal during the early stages of the disease (through two weeks); after this period imaging abnormalities indicative of central pontine myelinolysis emerge. MRI is more sensitive for diagnosing abnormalities than CT scan  . Comparison of changes between earlier and later CT or MRI scans is also useful.
CT scan images are prone to streak artifact in the region of the pons (and thus not as sensitive as MRI). CT scan may reveal low attenuation crossing the midline in the lower pons.
On T2-weighted MRI scans, areas of demyelination are marked by hyperintense and bright areas. T1 signal may be mildly or moderately hypointense; fluid attenuation inversion recovery (FLAIR) signal will usually appear hyperintense. A classic trident shaped pattern is indicative of ventrolateral pons, corticospinal tract, and tegmentum sparing. Extrapontine lesions are usually bilateral; they are commonly found on the cerebellar peduncles, globus pallidus, lateral geniculate body, thalamus, and putamen  .
Cerebral spinal fluid evaluation may show an elevated opening pressure, mononuclear pleocytosis, or an elevated protein level.
Few advanced neuroimaging studies like positron emission tomography have been studied for its efficacy in the diagnosis of central pontine myelinosis; studies have shown a high FDG-18 uptake initially, followed by decreased uptake in affected regions .
Electroencephalography (EEG) can be used to supplement imaging results, particularly when neuroimaging is not definitive. EEG usually reveals diffuse bihemispheric slowing in patients with central pontine myelinolysis.