If am having optic neuritis and brain lesions but its not ms, what are the other possible conditions?

Many causes : Many potential causes including ischemic & embolic (like stroke) demyelination (like MA), nerve compression. Hope that helps

THE USUAL SUSPECTS: Although this could be "Clinically Isolated Syndrome", with eventual clinically definite MS, other considerations could include an NMO spectrum disorder (get NMO-IGg, aquaporin-4 antigen), but consider sarcoid, a vasculits like lupus, Lyme disease, HIV, syphilis, Sjogren's, and perhaps B-12 issue. Statistically, you have >80% chance of MS confirmation within next 14 yrs, if only one lesion.