She notes that people with MS retain their abilities with regard to intelligence tests. They are able to reason and solve problems. Just because they are slow to respond to a question does not mean that they do not know the answer. It is rather a sign of other problems. They may not be able to connect the thought with appropriate words or may be having problems concentrating on the question.
Slowness is a failure of speed rather a failure of ability.
MS is a confusing disease. The causes are unknown. There is no absolute treatment. There is no known cure. However, in addition to all of this, the actual symptoms are extremely varied in kind and degree.