Donna, a 42-year-old mother of two, has been experiencing intermittent tingling and numbness in both of her feet. She has also had trouble holding a pen while writing. In the past few months, the tingling and numbness in her extremities seemed to subside on its own, so she was not very concerned. Recently, though, the symptoms have spread to her knees and thighs and are persisting. Yesterday, she stumbled when getting out of bed in the morning. When she tried to stand, her right leg was too weak to hold her weight and she fell again. She noticed that she scraped her right knee during the fall, but does not feel any pain from the wound. Donna notices that she has blurry vision and thinks that might be the reason she fell.