Except perhaps among people with primary progressive MS, implicit memory is not usually affected. On the other hand, people with MS may experience problems with explicit memory.  Explicit memory is also sometimes classified as being immediate (lasting seconds), recent (minutes, hours, or days) or remote (years in the past).   All of these aspects of memory may be affected in MS, but immediate memory may be less affected than other aspects of memory.  In practice, people with MS may find it difficult to recall and describe details of a book or a movie.

In a review of multiple studies, a strong relationship between memory problems and both disease duration and neurological disability has been observed; in other words, those with more physical limitations tend to have more difficulty with memory.  However, such problems may also occur relatively early in the disease and among people with few physical limitations.

Attention and Information-Processing Speed (22-25%): Because the processing of information quickly also requires attention, these are often discussed together. Some people with MS may have trouble with complex tasks, such as adding a series of numbers in their head.  Some measures of information-processing speed seem to relate to the amount of damage seen on MRIs of the brain.  People with deficits in this area may have trouble keeping up with details of conversation and may not be ready to move on in a conversation when others try.  Visuoaspatial difficulties may interfere with driving ability and driving safety.

Visual-spatial skills (12-19%):  Visual spatial skills include judging the relationship of lines and angles and perceiving of faces. People with problems in this area might have trouble recognizing faces or driving. 

Conceptual reasoning (13-19%):  Conceptual reasoning includes the ability to solve problems and demonstrate flexibility in reasoning.  In particular, people with MS may be prone to perseverative errors, which means that they may persist (or persevere) with an approach to a problem despite evidence that the approach is not working.  While some evidence indicates that this problem occurs frequently, there is other evidence to show that the magnitude of this particular aspect of cognitive dysfunction may be relatively small.  People with this particular problem might note difficulty adapting to change in the work place.

III. Identifying Cognitive Impairment and Its Causes

Sorting out various factors that contribute to cognitive dysfunction is essential.  For example, memory and attention problems may be caused by depression, and the incidence of depression in MS is particularly high. Other potential causes of cognitive complaints include sleep problems, fatigue, stress, other medical conditions (such as thyroid abnormalities) and medication side effects.  A partial list of medications that might worsen or cause cognitive problems follows:

·     Baclofen (lioresal),

·     Decadron (dexamethasone).  

·     Deltasone (prednisone), and

·     Detrol (tolterodine),

·     Dilantin (phenytoin),

·     Ditropan (oxybutin),

·     Klonopin (clonazepam),

·     Neurontin (gabapentin),

·     Valium (diazepam),

·     Zanaflex (tizanadine),

Many causes of cognitive dysfunction can be addressed or treated once identified.  For this reason, careful evaluation is critical.  Those with concerns about cognitive dysfunction should discuss the issue with their health care provider.  Under some circumstances, a referral to a specialist, a neuropsychologist, who has training in both neurology and psychology, will be useful.