Approximately one-half of all people with multiple sclerosis (MS) experience cognitive impairments, such as difficulty with concentration, attention, memory, and poor judgment.
These symptoms are usually mild and are frequently overlooked. In most cases, they are only detectable through in-depth, neuropsychiatric testing.
Patients themselves may be unaware of their cognitive loss. It is often a family member or friend who first notices a change. Such impairments are rarely disabling, and intellectual and language abilities remain intact.
Cognitive symptoms due to multiple sclerosis occurs when lesions develop in brain areas responsible for information processing. These deficits may be more apparent with more complex or challenging processes.
MS-related fatigue may also make it more difficult for someone with multiple sclerosis to process information.
Scientists do not yet know whether altered cognition in multiple sclerosis reflects problems with information acquisition, retrieval, or a combination of both. Types of memory problems may differ depending on the individual's disease course (relapsing-remitting MS, primary-progressive MS,... etc.). However, there does not appear to be any direct correlation between duration of illness and severity of cognitive dysfunction.
Reference: The National Institute of Neurological Diseases and Stroke (NINDS)