Multiple Sclerosis is a devastating disease that has no cure.
Patients suffer problems with vision, balance, muscle control and fatigue.
Treatments have progressed over the years and now a new drug called Lemtrada is offering very encouraging results.
As part of our tribute to 70 years of the National Health Service, Stacey Poole has been speaking to Karen Flewin throughout her journey taking Lemtrada.
Part One - Karen before taking Lemtrada
At just 40 years old and with a young daughter, her condition is deteriorating rapidly.
So she's agreed to have this new drug treatment, but it is not without it's risks.
Part Two - Karen begins treatment
Interviewee: Prof Richard Nicholas Consultant Neurologist
Karen often loses her sight and the feeling down one side of her body.
In part three Karen has undergone a 5 day infusion of the drug.
It is a gruelling treatment that has left her feeling terrible.
Part Three - Post-treatment