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 your doctor.
Without the ability to examine your mother and obtain a history, I can not tell you what the exact cause of her symptoms is. However I will try to provide you with some useful information.
Your mother's symptoms of episodic severe headache followed by other neurologic symptoms could be consistent with migraine. While confusion and memory problems during migraine is most commonly an occurrence in children, in which case it is called confusional migraine, this can occasionally happen in adults as well. Two normal MRIs of the brain does rule out stroke; I am not sure what you mean above by "CT showed seizure" and I do not exactly understand what abnormality the CT showed, but with 2 normal MRIs, the majority of tumors, vascular malformations, bleeds etc can be ruled out.
One condition in older adults that causes headaches with other neurologic symptoms is vasculitis. However, the headaches and symptoms would not be episodic with return to normal as it sounds like is the case in your mother, but rather constant and progressive. Vasculitis basically means inflammation of the blood vessels; this can be either due to autoimmune/rheumatologic disorders like lupus, or can be what is called primary CNS vasculitis, or vasculitis that occurs only in the blood vessels in the brain without a systemic cause. Vasculitis is diagnosed based on history, examination, imaging of blood vessels of the brain (which can be accomplished with an MRA or CT angiogram but the most sensitive test is a standard cerebral angiogram). Lumbar puncture to analyze the cerebrospinal fluid, the fluid that bathes the brain and spine, can sometimes be helpful.
Lupus is diagnosed based on a combination of clinical signs, organs involved, and specific blood tests. A photosensitive rash can occur in lupus, but a rash in isolation does not diagnose systemic lupus.
In people above the age of 55, one potential cause of headaches is called giant cell arteritis or temporal arteritis. This is due to an inflammation in the temporal artery and other arteries in the body. Symptoms include one sided headache pain in the temple and jaw that may be triggered by chewing. This condition can be diagnosed by a blood test called an ESR and a biopsy of the artery. If the ESR is normal, this diagnosis becomes unlikely. It is treatable with corticosteroids.
I recommend continued follow up with your neurologist. If a vasculitis is suspected, evaluation by a rheumatologist may be indicated.
Thank you for this opportunity to answer your questions, I hope you find the information I have provided useful, good luck.
I neglected to mention that my mother was diagnosed with fibromyalgia in 2000 and that she has recently had strange rashes appear on her arms, legs and back. They do not hurt or itch. They are just raised discolorations that come and go. Her skin is left leathery-like. She also gets a rash when she goes out in the sun. I believe some of this was the reason the nurse mentioned lupus. I do not know if any of this is related to her current problem.
Lisa