Multiple sclerosis and cognitive disorders: what are they?

What is multiple sclerosis (MS)? 

Multiple sclerosis (MS) affects more than 1 million people in the United States, with about 12,000 new cases diagnosed each year. The average age of the disease onset is 30.

It is an inflammatory disease of the central nervous system: the brain, spinal cord and optic nerves. The immune system, normally involved in the fight against viruses and bacteria, attacks the myelin (protective sheath of nerve fibers) which plays an important role in the propagation of nerve impulses from the brain to various parts of the body.

The signs and symptoms observed at the start of the disease vary depending on the location of the lesions in the brain or spinal cord. They include motor problems, sensory disorders, balance problems, visual and/or urinary problems, and are often transient, as multiple sclerosis progresses in relapses.

MS can therefore cause a range of motor, sensory, psychological and cognitive symptoms. The course and manifestation of the disease are extremely unpredictable.

What cognitive disorders are caused by MS? 

During the course of the disease, lesions occur in the brain. Depending on the areas affected by these lesions, motor disorders may appear, leading, for example, to difficulties in walking.

Similarly, these lesions can cause changes in the way the brain functions. This does not mean that intellectual capacity diminishes, but that certain mechanisms in the brain's cognitive networks may be altered.

Cognitive disorders are common in multiple sclerosis. Their prevalence varies between 40% and 70% according to published studies. Most patients experience mild or moderate impairment, while around 10% experience more severe symptoms.

Several cognitive areas are affected by multiple sclerosis:

The speed of information processing 

Cognitive problems in multiple sclerosis are dominated by a slowdown in the speed with which information is processed. This slowing is 10 times more frequent in MS patients than in the general population. It is even more common in patients with secondary progressive multiple sclerosis (occurs 65 times more often than in the general population). Other studies have shown that individuals affected by MS are 40% slower than healthy subjects on processing speed tasks.

Learning and memory 

Memory is important in all the tasks we carry out on a daily basis, and it is quite easy to notice when it fails us. People affected by multiple sclerosis frequently complain of memory problems. Problems with learning and memory in MS patients concern working (a form of short-term memory which enables us to store and manipulate information for a short period of time) and episodic memory (which enables us to situate ourselves in time and space and thus to project ourselves into the future).  

Attention 

Attention is required for virtually all daily tasks. It enables us to concentrate on the work we are doing, integrate data, understand information, whether oral or written, and express thoughts.

The mechanisms behind attention are numerous. Some studies show that MS patients suffer from global attentional impairment, while others show that it is the most complex forms of attention that seem to be most affected. This is particularly true when it comes to dividing attention between several tasks simultaneously or sustaining attention for a certain length of time. When performing tasks requires constant mental effort, patients show a progressive deterioration in their performance. This is known as 'cognitive fatigue'.

What are the consequences of cognitive disorders on the everyday life of patients with MS? 

Even moderate cognitive difficulties linked to multiple sclerosis should be taken seriously.

Cognitive problems can have a major impact on daily life when, for example, it becomes difficult to deal with situations that require a quick reaction. In a professional context, this can have even greater consequences: if a person needs more time than before to do their job, it's not uncommon for them to be criticized for it.

That's why it's so important to detect cognitive impairment as early as possible.

Early detection means that patients do not feel guilty about the difficulties they may be experiencing, and specific treatment can be offered.

There are some tests that can be used to detect cognitive problems, they can be prescribed either by a neurologist or a neuropsychologist. These tests will reveal the nature and degree of the cognitive problems the person experiences.

How can cognitive disorders caused by MS be managed and treated? 

To date, no drug treatment has been shown to be effective in treating cognitive disorders caused by MS. However, cognitive re-education approach has been developed in recent years.

This cognitive re-education approach is generally carried out in conjunction with a speech therapist and are often offered as part of MS care plans.

The aim of cognitive re-education is to stimulate the brain through a series of exercises tailored to the difficulties identified in the patient.

These exercises can focus on memory, attention, information processing, etc.

Because the brain is highly flexible, it is capable of constant adaptation. Thanks to cognitive re-education, the brain will be able to use "compensation networks" and compensate for areas that function less well as a result of damage caused by MS.

The frequency and repetition of training sessions will enable real progress to be made. In general, cognitive re-education programs involve several sessions a week (usually 2 to 3) for the duration of several months (usually 4 to 5 months).

Once these 4 to 5 months have elapsed, additional sessions, spaced out over a longer period of time, may be offered depending on the patient's needs.