When the myelin sheath that covers nerve cells is destroyed, signals from one nerve to another aren't properly transmitted. Although the brainstem is mainly affected, other areas of the brain can also be involved.

The most common cause of ODS is a quick change in the body's sodium levels. This most often occurs when someone is being treated for low blood sodium (hyponatremia) and the sodium is replaced too fast. Sometimes, it occurs when a high level of sodium in the body (hypernatremia) is corrected too quickly.

ODS does not usually occur on its own. Most often, it's a complication of treatment for other problems, or from the other problems themselves.

Risks include: