Central Pontine Myelinolysis (CPM)

Timothy C. Hain, MD • Page last modified: April 13, 2021

Central pontine myelinolysis is a rare cause of damage to the brainstem. First described by Adams et al. in 1959 in their chronic alcoholic patients, it has now been described in the malnourished, the chronically debilitated, the renal patients, the hepatic and the transplant patient among others. There is an extensive literature concerning CPM, with more than 500 publications having "central pontine myelinolysis" in the title in Pubmed as of 2021.

According to Singh et al in their systemic review (2014), "the most common presentation was encephalopathy (39%)." In other words, depression of consciousness, possibly including coma.

CPM is attributed to rapid fluctuations in electrolyte status, usually in the context of a hospitalization. About 2% of persons with liver transplant develop central pontine myelinolysis. Some cases of CPM appear to be triggered solely by alcohol withdrawal (Yoon et al, 2008).

According to Lempl, as of 2006, 174 cases of CPM have been reported in alcoholics since 1986, which is equivalent to an incidence of 39.4% (of alcoholism in CPM). Thus chronic alcoholism is still the most common underlying condition of CPM patients. Likewise, 95 cases of CPM following the correction of hyponatremia have been documented since 1986 (21.5%). The third largest group of CPM cases are liver transplant patients (17.4%), with the development of CPM being attributed to the immunosuppressive agent cyclosporine in particular. There are also case reports of CPM attributed to hyperglycemia (high blood sugar) but CPM is "rarely seen in diabetics" (Talluri et al, 2017).

Diagnosis

Pathologically, it is defined as a symmetric area of myelin disruption in the center of the basis pontis, although similar symmetric lesions have also been described occurring with CPM as well as independently in other brain areas (extrapontine myelinolysis or EPM) including the cerebellar and neocortical white/gray junctional areas, thalamus and striatum.

Clinically, patients often are unable to move their eyes during their acute period, may be "locked in" -- with quadraparesis, and have speech disturbance.

Case example 1: osmotic syndrome. a patient presented to the clinic complaining of chronic dizziness and imbalance. During a hospitalization for pancreatitis, he became hyponatremic. An MRI scan showed "poorly defined high T2 signal within the central pons". Physical examination revealed slowing of upgoing saccades and positional nystagmus.

Case 2: Liver transplant. The individual shown below had a liver transplant done. After the liver transplant, he was fine for a couple of days but then gradually became comatose. His MRI at that time showed the picture above. Examination nine months later revealed an ambulatory individual with some mild cerebellar signs.

MRI scan of person with central pontine myelinolysis. sagittal view. The dark area inside the circle is the region of damage.

© Timothy C. Hain, M.D.

MRI scan of person with central pontine myelinolysis, axial view. Note the "I" shaped area in the center of the pons. This resembles the "hot cross buns" sign of MSA (see below).

Not all white spots in the pons are caused by CPM.

Other sources of pontine high signal include small vessel disease (Xia et al, 2017). This is far more common than CPM. This shows up as a white "cloud" in the center of the pons, as shown above. The first patient had several vascular risk factors, including labile hypertension, and also had many white matter lesions in the cortex.The patient in example 2 was just 80. We think this type of pontine white matter change would be difficult to distinguish, based on MRI findings, from CPM. Kleinschmidt-Demasters (1997) followed up some of these on autopsy and found that most lesions like this are ischemic rather than due to central pontine myelinolysis. Thus the CPM diagnosis requires a cause.

The "Clipper's" syndrome is an autoimmune disorder that is another cause of white matter lesions in the pons, but these are vascular structures that light up on contrast.

Another brain disorder, Multiple systems atrophy, also has a similar appearing streaky white appearance to the pons. This is a neurodegenerative disorder.

Pontine white matter disease
Small vessel disease in the pons
There is a "cloud" in the central pons, in this unsteady patient with no history of a source of CPM. Imaging type is Flair.

 

Pontine white matter disease Example 2
Central pontine small vessel disease example 2
There is a "cloud" in the central pons, in this 80 year old patient with no history of a source of CPM. Imaging type is T2 Flair.

 

Mechanism of CPM

According to Kumar and associates (2006), "Central pontine myelinolysis (CPM) can be regarded as one of the demyelinating syndromes."

Possible mechanisms include a hyperosmotically induced demyelination process resulting from rapid intracellular/ extracellular to intravascular water shifts producing relative glial dehydration and myelin degradation and/or oligodendroglial apoptosis.

Treatment of CPM

Avoidance of CPM is dependent upon recognizing those patients with conditions predisposing them to osmotic myelinolysis and then moderating the rate of normalization of the electrolyte imbalance. Acutely, treatment after the CPM has developed is mainly supportive, but successful treatment with a variety of agents including plasmapheresis (Grimaldi et al, 2005) and TRH (Zein et al, 2006) have been reported. It is difficult to see the rationale for these treatments.

According to Singh et al (2014), who used the term ODS to include both CPM and extrapontine myelinolysis, "Favorable recovery occurred in 51.9% of patients and death in 24.8%. Liver transplant patients with ODS had a combined rate of death and disability of 77.4%, compared with 44.7% in those without liver transplantation (P < 0.001). ODS is found to have a good recovery in more than half of cases and its mortality has decreased with each passing decade. Favorable prognosis is possible in patients of ODS, even with severe neurological presentation." This paper goes a bit beyond the scope of CPM of course but it is the most comprehensive in the literature as of 2021..

For persons with CPM symptoms that persists after several months, we sometimes attempt to manage them for "central dizziness", sometimes using physical therapy (Raceti et al, 2020). Generally speaking, after the acute event has resolved, medications are not helpful for patients with chronic consequences of CPM.

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