Deenie... sorry you are having to deal with this with your husband but so glad you found us. Everything you have described here is text book dementia. Variations of this story is the same for just about everyone who deals with this disease.
We noticed symptoms in the beginning but do not connect it to cognitive loss. It's a bad day, they are stressed, it was a one time incident are some of the things we think. But when that one incident happens (as hubby losing his car) we stand back and wonder. He did not just get dementia when he was diagnosed... it has been present in a very mild for for years. It just got bad enough that a decision was made to find out what was going on.
Nothing will show in the medical test except perhaps some minor atrophy on the MRI. Unless you have a previous MRI for comparison it may not even be mentioned. If diagnosed early enough it will not even show up. There is no blood test for dementia. They just rule out many other causes. The Neurologist or PCP should have given him a memory test. That is the best way to know if there is a cognitive decline. Then you rule out everything else and dementia is what is left.
The blocked arteries can be causing Vascular Dementia if there are blockages in the brain. My Dad had Vascular Dementia. It is the second leading cause of dementia. It may also be mixed Dementia involving both Vascular and Alzheimer's... or other dementia types. Aricept is one of the Memory medications that is supposed to improve cognition. It works for a small percentage of people to slow down the progression. It does not reverse, cure, or stop the progression of the disease and it does have side effects. Please discuss the side effects with your pharmacist. They are much more informed about medication than your doctor. Considering his behavioral changes after the Aricept I would definitely talk to the pharmacist.
Seroquil is used frequently for behavioral changes in those with dementia. Some respond well, as your husband. Hopefully his outburst are under control. These outburst are a function of his cognitive decline. Not only is his memory impaired but his ability to understand and respond correctly. You may never know what angered him because it was something in his brain, not something you did. His inability to comprehend what is going on is the problem. Once he is agitated he is less able to understand. He responds on a basic fight or flight adrenalin level. You did what was best. You also need to know that he can not tell you what is going on in his mind. He doesn't have the words and ability to explain what he is feeling... he is just reacting.
Evenings are usually worse. It is known as Sundowning. Science does not have a explanation but it is a known reaction to the end of the day by many if not most with dementia. It may help if you keep the house well lit at that time of day, keep life routine and calm, and avoid triggers that upset him. Sometimes a nap late in the day can help as well to avoid him being over tired at this time of day.
Making decision, ordering from a menu, and such involve cognitive awareness that he obviously no longer has. For Dad, and Mom (who has Alzheimer's) I would make suggestions. "I would like to go out to eat." That indicates I would like to go out to eat and it is a yes or no answer. Makes it easy for them. Once there I would say... "You always loved the XXX". That gave him one choice, yes or no, and much easier then dealing with all those words on the menu. If you know he has difficulty with even simple decision you can help him by making it easy.
Crowds and loud noises will bother him because he can no longer deal with all the sensory input. They ability to focus is lost so they can not separate conversations. They hear everything at the same level and that is overwhelming. Large crowds are over stimulating when you don't know what to do. Loud noises are startling. They have no basis for these noises and jump as we do when we hear something we can't identify.
Routine is going to be your friend. Keeping him in a set routine will make him calmer.... and your life better. We like to go out. We like noisy crowds and excitement. They totally and completely overwhelm his ability to deal. I quiet dinner for two at home will become the best times.
Since he has gotten lost already you need to be aware of wandering. It is not unusual for someone with dementia to go out to get the mail and not come back. Keep an eye on him and be sure there are locks on the doors at night that he is unfamiliar with.
A word to the wise. If you do not have durable power of attorney, medical power of attorney, will, and living will done for him please do it NOW. It will make life so much easier later when you are responsible for his total care. Also make sure you name is on all accounts... banking, financial, utilities, credit cards... everything. That way you will not have a problem when changes need to be made. A good elder lawyer can help you with this. Check prices because not all are the same. If cost is a problem call the bar association and find a lawyer that can do it pro bono in your area. Just please get this done ASAP.
Again... glad you found us and know each of us here is going through the same things. We are here to support each other and here for you