Dementia in multiple sclerosis: why is it rarely discussed?

Cognitive deficits in multiple sclerosis (MS) have been well studied in decades of MS research. Severe deficits are acknowledged, but the frequency is minimized in the literature, and there is a striking lack of discussion of the presence of a dementia state in MS. Possible reasons for this omission are discussed, along with an argument to define the dementia state and to provide terminology that will be palatable to patients.