Doctors typically diagnose MS with a laboratory test called an MRI - Magnetic Resonance Imaging. This test simply provides doctors a picture of your brain, spine, and nerves so s/he can look for scarring.

Diagnosing a person with MS can be a tricky thing to do because everybody's symptoms can be different and because some of the symptoms are also warning signs of other diseases of the central nervous system.

In order to establish a diagnosis of MS, there must be one or more area of malfunction in the central nervous system and these malfunctions must have appeared at least two separate times.

These pictures are from actual MRIs conducted on people where doctors detected scarring which is a main indication of MS.
(Source: MS Tutorial - www-medlib.med.utah.edu/kw/ms)