MS symptoms can be vague, and many other neurological problems can have similar symptoms, even scans cannot always tell.
[link removed] will give you some idea of how many other diseases show similarities.

First I was diagnosed with MG (left eye and face drooping; extreme weakness in legs and arms; I can't look up at all; double vision to the left and right and when looking up; bad balance problems; choking; weakness in voice). Tests came back negative. Now symptoms are extremely worse. Extreme pins & needle feelings in arms, legs, feet, across the back, across the stomach, across the chest and the buttocks. I can barely walk, with a schuffling; It's extremely difficult to get up and down out of a chair or climbing steps; the weakness has gotten extremely worse; Pins & needles worse; lost feeling in feet and parts of legs (I burnt my left knee on a heater and didn't even feel it); my right heel around the edges of the heel is extremely painful and increase when I'm on my feet a lot. It keeps me from sleeping; it doesn't stop when I'm off of my feet or have my legs up on the couch and I get sharp blairing pains that shoot up; I feel short of breath or my breathing is labored. My blood work and spinal tap also came back normal. My neurologist advised that she feels it's MS. I am going to have another MRI with a MRA this coming Mon. as there were some spots on the last MRI 10/08 but nothing really definite. I've had blood work, CT head, MRI head, cervical and lumbar (I have 1 bulging disc in cervical & lumbar with stenosis). This has been going on since May 08 and I'm just so frustrated. Please advise if there are other diseases that mimic MS. Thanks so much.

Chronic Fatigue Syndrome/fibromyalgia can mimic many MS symptoms. Benzodiazepine and SSRI withdrawal syndrome also.