There is a test that is done ( mine took 6 hours the first time and 3 hours the next) that that call a neuropsych test. It is a lot like a really long IQ test but what it does is see how each part of your brain is working and what, if any, damage has been done. When mine was done they found that my short term memory has been damaged (borderline deficient on the 1st and waiting the results of the 2nd) and my motor skills have been damaged on both sides but the most damage has been done on my right side (deficient on the right and borderline on the left). It also found that I had depression (ya think?) and my last MRI showed a decreased blood flow to my brain. So the answer to your question is yes, they can be diagnosed and I am afraid that I am stuck like this forever. There are memory building things that I can do to try and help but honestly they only upset me because they are a constant reminder of how far down I have fallen.
I broke down crying during my first neuropsych partially from relief that there was proof and partially because I knew my life as it had been was over. I had hoped that I could one day go back to work and be able to grasp the legal documents that I had been reading for years and fixing the issues that I had become so good at fixing. This showed me that it would be no more. It doesn't mean my life is over but the rest will be very different from what I had known before.
Success is not final, failure is not fatal: it is the courage to continue that counts.