Osmotic demyelination syndrome
Updates to Article Attributes
Central pontine myelinolysis (CPM) (also known as osmotic demyelination) refers to acute demyelination of the white matter tracts traversing the pons. It seen in the setting of osmotic changes, typically with the rapid correction of hyponatraemia. Despite the name extrapontine structures can also be affected: basal ganglia, midbrain and subcortical white matter. It is then known as extrapontine myelinolysis (EPM).
Demographics and clinical presentation
The initial description of CPM by Adams et al in 1959 2 was entirely in a population of chronic alcoholics, and certainly this scenario is common. Since then it has been increasingly recognised in other patient groups, but usually in the setting of rapidly corrected electrolyte disturbance:
- chronic alcoholics
- chronically debilitated patients
- transplant recipients
Clinically CPM presents in a biphasic pattern. The first phase is usually attributable not to the demyelination but rather to the inciting electrolyte abnormality, with patients being acutely encephalopathic. Following rapid reversal of this abnormality the patient transiently improves before progressing onto the classic CPM features 2-3 days later. These consist of:
- spastic quadriparesis
- pseudobulbar palsy
- changes in levels of consciousness
- coma or death
Pathology
Although the exact mechanism is still uncertain, it is known that oligodendroglial cells are most susceptible to osmotic stresses, leading to their demise. It is not surprising that the distribution of osmotic myelinolysis therefore parallels the distribution of these cells.
Histologically CPM is characterised by intramyelinitic splitting, vacuolisation and myelin sheath rupture 3. After a number of days macrophages can be identified.
Radiographic features
CT
CT may demonstrate low attenuation crossing the midline in the lower pons, although this region is frequently degraded by streak artifact and beam hardening phenomenon.
MRI
The earliest change is seen on DWI with restriction in the lower pons. This is seen within 24 hours of the onset of quadriplegia 3. This same region demonstrates eventual high T2 signal and later low T1 signal. The T1 and T2 changes may take up to two weeks to develop. This region has a classic trident shaped appearance. Occasionally gadolinium enhancement is also demonstrated, just as in the acute phase of an multiple sclerosis (MS) plaque. The peripheral fibers (ventrolateral longitudinal fibers) as well as the periventricular and sub pial regions are typically spared.
Signal characteristics of affected region includes
- T1: mildly or moderatly hypointense
- T2: hyperintense, sparing the periphery and corticospinal tracts
- PD: hyperintense
- FLAIR: hyperintense
- DWI: hyperintense
- ADC: signal low or signal loss
-
T1 C+ (Gd):
no enhancementmay enhance5 (4/14 cases in Graff-Radford et al 20116)
PET
Affected regions may demonstrate initial high uptake followed by subsequent low uptake with 18-FDG.
Differential diagnosis
General imaging differential considerations include:
- demyelination including multiple sclerosis (MS)
- infarction from basilar perforators can be central, although usually brainstem infracts stop at the midline
- pontine neoplasms including astrocytomas
-<strong>T1 C+ (Gd):</strong> no enhancement</li>- +<strong>T1 C+ (Gd):</strong> may enhance<sup>5</sup> (4/14 cases in Graff-Radford <em>et al</em> 2011<sup>6</sup>)</li>
References changed:
- 5. Juergenson I, Zappini F, Fiaschi A, Tonin P, Bonetti B. Teaching neuroimages: neuroradiologic findings in pontine and extrapontine myelinolysis: clue for the pathogenesis? Neurology. 2012 Jan 3;78(1):e1-2. doi: 10.1212/WNL.0b013e31823ed0b5. <a href="http://www.ncbi.nlm.nih.gov/pubmed/22201117">Pubmed citation</a><span class="ref_v3"></span>
- 6. Jonathan Graff-Radford, Jennifer E. Fugate, Timothy J. Kaufmann, Jay N. Mandrekar, and Alejandro A. Rabinstein. Mayo Clin Proc. Nov 2011; 86(11): 1063–1067. <a href="http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3202996/">Pubmed citation</a><span class="ref_v3"></span>
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