There are several diseases and conditions that mimic MS. Following is a list by type. I'm not guaranteeing that these are all of them, but it's a pretty good list.
Human T-cell lymphotrophic virus-1
Central Nervous System Angitis
Dural Arteriovenous Fistulas
Other Diseases and Conditions:
Vitamin B12 deficiency
Amyotrophic lateral sclerosis (ALS or Lou Gehrig's disease)
The Multiple Sclerosis Foundation published an article that talks about these mimicing conditions in detail. This article tells how each condition is similar to MS, and then why it is different.
I hope this list and link provide you with the information you need. If not, perhaps a chat with your doctor would be more helpful. Good luck.