Eventually relapsing-remitting MS can become progressive MS as the good spells become shorter and less frequent.

BBC: Multiple sclerosis: New drug 'most effective'

When the condition is diagnosed most will have a form of the disease know as relapsing-remitting MS, in which the symptoms can almost disappear for a time, before suddenly returning.

BBC: Multiple sclerosis: New drug 'most effective'

Beta-interferon has also been shown in studies to benefit to those with "relapsing-remitting" MS, in which the sufferer's condition is stable in between "attacks", which prove gradually more disabling.

BBC: MS drug 'should be restricted'

There are different types of MS - most people with the condition have the relapsing remitting type where the symptoms come and go over days, weeks or months.

BBC: Simple eye scan can reveal extent of Multiple Sclerosis