Thanks for using the forum. I am happy to address your questions, and my answer will be based on the information you provided here. Please make sure you recognize that this forum is for educational purposes only, and it does not substitute for a formal office visit with a doctor.
Without the ability to examine and obtain a history, I cannot tell you what the exact cause of the symptoms is. However I will try to provide you with some useful information.
I am sorry to hear about the difficulties that you are experiencing. Since you have already had some diagnostic tests completed, many of the following possibilities may have been ruled out. You have likely already had routine bloodwork to ensure that your blood counts are normal, and that there is no electrolyte imbalance. It sounds like hypothyroidism has already been ruled out, and that you are being checked for vitamin deficiencies. A potential cause of dementia or encephalopathy in young patients is HIV. If an HIV test has not been performed, I would consider getting a screening test. Toxic exposures, including chronic alcoholism, can also be a culprit.
A less likely possibility with a normal MRI and the absence of other neurological symptoms is that there is a brain lesion that is causing your memory loss/confusion. I am using a very general term in brain lesion, as there can be many different causes of lesions in the brain including autoimmune, malignancy, vascular, or infectious.
Seizures are also a consideration, especially if your symptoms appear to be occurring episodically. Seizures can present as confusion or memory loss, and do not necessarily need to have motor involvement. A normal EEG may not necessarily rule out this possibility, especially if you did not experience any symptoms during monitoring.
Another group of problems that can cause thinking problems and fatigue are psychiatric. Clinical (medical) depression and anxiety can sometimes be expressed in this way. Also, attention deficit disorder (ADD) may sometimes be the cause of concentration and memory difficulties. Many people think of this as a childhood disorder but it can start in childhood and not be diagnosed until adulthood.
Thank you for this opportunity to answer your questions, I wish the best of luck to your and your physicians in figuring out the cause of your symptoms.
Thank you so much for your response. Lots of good information, thank you! And my doctor had kind of hinted that the tests that were "negative" were all absolute, & could not be a false negative. I was especially curious that EEGs can be falsely negative, as I asked my doc about that also. Because common sense tells me that if I'm not in the middle of a seizure at THAT moment, then couldn't the result be "negative"??? I was assured that it would show SOME abnormal brain function if I had even slight seizures. I will look into that more & ask my primary doc about what she thinks.
I am currently waiting on a 2nd round of blood tests: retesting thyroid function, vitamin B12, and mercury levels (I have a lot of "silver" dental fillings that they brought up). I believe a sleep study will be next if all those are "negative", & then a visit to a psychologist was also my request. :) I DO have ADD, diagnosed at 27 (and I'm 36 now). But this feels quite different than my usual ADD symptoms.
The only question I had left, was about the brain lesions occurring with a "normal" MRI. So, how would they FIND any brain lesion (if that were the cause) if it doesn't show up on MRI? Not that I'm worried it is something that severe, I feel it will be a far simpler explanation, but it's scary to think something like a brain lesion COULD occur with all tests being "normal"! :)
Well, thank you, again, for your response. Gave me enough information to know they're at least looking for some of the possible culprits already, & now I may ask about the EEG again.
Thanks so much!