I think the words of a Neurology Forum Expert sums up when you can see abnormal evoked potentials best:
http://www.medhelp.org/forums/neuro/messages/30149.html
He/she states:
"ANYTHING which interferes with the function of the nerve fibers will cause an abnormal test result. The test only proves that there is some problem, somewhere but it is not at all specific as to the identity of the underlying disease. becuuse of this the test must be interpreted in context, that is in the context of your symptoms, the findings on physical examination and the results of other supportive tests like the spinal tap and MRI."
I did a little bit of noodling around to get some examples. Things like acute viral encephalitis, acute cerebellar ataxia, Acute Disseminated EncephaloMyelitis (ADEM), tumors (benign and malignant), Systemic Lupus Erythematosis (SLE or Lupus), likely any rheumatologic disease that can cause a cerebritis (brain inflammation). It's late at night so that is where I stopped.
So, I found that any thing that damages the nerves of the central nervous system can cause abnormal (slowed) evoked potential results.
Yes, this test is often used when trying to nail down MS, but it is not nearly sensitive or specific enough to be a defining test for MS.
Of the things I listed, Lupus and ADEM are really on the list of mimics of MS. As far as severe B12 deficiency, or things like Lyme Disease or HIV, or Wilson's Disease etc., I don't know. Would have to look them up.
Welcome to our forum. Why don't you tell us what led to your having the sensory evoked potential? We have a lot of people with great experience and information here.
Quix