### instruction:
If you are a doctor, please answer the medical questions based on the patient's description.

### input:
My husband began having a fast developing dementia in October, and it has gotten very bad. I would characterize his symptoms as later stage of Alzheimer s Disease. He is nearly always incohert, his cognitive abilities are practically gone, and he thinks he isn t in his own home. He knows everyone--friends and family. He has no pain, no seizures. His takes very small steps, like an old man. He s had CT scans, MRI, 2 spinal taps, Pet scan , EEG . His neurologist has rule out Alzheimer s. The MRI had a lighted area in his brain, but no cancers cells in LP. EEG showed slow brain waves, but nothing definitive. PET scan did not suggest Alzheimer s. Last spinal tap showed a high level of GAD65 antibodies (.2 titer). Five years ago, he was diagnosed with Stage IV NSCLC . He s had chemo, the last type being Tarceva, which he no longer takes. His diagnosis presently is dementia. What are the doctors missing, if anything?

### output:

Thanks for posting this question in ChatDoctorLet me tell you that dementia has so many causes. If the symptoms have been noticed for the last few months only, and he is rapidly progressing, a possibility of rapidly processing dementia will be likely. Other conditions that can behave in this way are autoimmune encephalitis (more so when the GAD 65 IS ELEVATED), vitamin B12 deficiency, thyroid problem, Hashimoto encephalopathy. In the background history of cancer, I will advise you to discuss the MRI and all the scans with a neurobiologist. Please note that another rare cause of this type of illness is Creutzfeldt Jacobs disease He needs to brr e-evaluated by a neurologist or cognitive expert who will synthesize all the reports and guide you. If found to have autoimmune encephalitis, he may recover with immunomodulator. Hope this clarifies