To the Editor: Differentiating a manic episode of bipolar disorder from mania secondary to a medical condition in older adults is challenging. The diagnostic dilemma appears when the patient has an established diagnosis of bipolar disorder from a young age. The neuropsychiatric manifestations are similar, and there have been numerous conditions to which secondary mania can be attributed. A thorough differential diagnosis should be considered to help guide appropriate management. Evidence suggests that neurological conditions are the most common causes of secondary mania. In a retrospective study examining 50 manic patients older than age 65, neurological disorders were reported in 74% of the patients.1 We summarize a case of mania that emerged in the context of acute demyelinating encephalitis in an elderly patient with a diagnosis of bipolar disorder since adolescence.