b12 Deficiency also mimics MS see here http://www.b12d.org/MS-like-presentation & symptom check for B12 Deficiency here http://www.b12d.org/content/b12-signs-symptoms-assessment
Vitamin B12 Deficiency can mimic certain conditions. You will find a patient leaflet on The Pernicious Anaemia Society website. Doctors don't think about PA in one so young but there are cases that have a genetic cause. If you have B12d it can be treated with high dose B12 injections.
Symptoms of chiari malformation seem so similar to Multiple schlerosis, which can be extremely difficult to diagnose.
Have you researched MS? Often before diagnose patients develop a long history of what looks like complaining with no cause - before the diagnosis is finally made.