I'm sorry to hear about the struggles your husband is going through. I strongly empathize, as I have GERD, have had surgery, and still, until recently, had serious, non-specific symptoms that were getting progressively worse. This past summer, my wife thought I was going to die. I was also into bodybuilding since the age of 17 (now 51), and had always eaten well. I don't eat junk food, soda, coffee, or drink alcohol, and am also vegetarian.
You mention PPIs making things worse, which, coupled with the other symptoms you describe, is significant. Both of you may be resistant to what I am going to say. But I would strongly encourage you to explore food intolerance...specifically gluten and casein.
Food intolerance is a separate condition from food allergy. Food allergy usually produces severe symptoms within 30 minutes, while food intolerance is more subtle, and symptoms appear from 12 to 72 hours later. Food intolerance causes an autoimmune reaction, and, depending upon the individual, can manifest in a host of different ways.
Your husband's first reaction will undoubtedly be, "I don't have food intolerance. I've eaten the same things my entire life and never experienced indigestion." I never experienced indigestion, either. When we are young, and our immune systems are more robust, food intolerance stays in check. When it appears later in life, it's called an "adult onset" condition, but all that says is that your body is finally weakened to the point that the symptoms become obvious.
Two symptom categories of gluten intolerance that are considered more serious, are gluten-induced neuropathy and gluten ataxia. At the worst of my symptoms before I discovered my intolerance, I had crushing migraines 3-4 times per week, cognition/memory issues, "brain-fog," etc. Also depression, apathy, and chronic fatigue, in addition to joint pain/arthritis, asthma, and muscle weakness. I also had blurry vision in my left eye especially, and watering, stinging eyes. This symptom actually got worse on the diet. I discovered that this is not an uncommon symptom, and is caused by B2 deficiency as a result of damage to the small intestine. The reason the symptom gets worse on the diet is because grains and cereals are eliminated, which are among the main contributors of B-vitamins (but only because they are artificially fortified!) I supplemented B2, and the symptom reversed in 24-48 hours. There are other deficiencies associated with intolerance, which include all the B vitamins and D as well. I recommend seeing your doctor and getting blood tests, as well as a celiac panel. It's quite possible that your husband's B12 and folate will come back in the normal range, but this is because these are imperfect serum-level tests. You should also do methylmalonic acid (MMA), because this evaluates B12 metabolism on a cellular level, and also gives a window into homocysteine levels -- another important consideration.
Other intolerance patients note the neural symptoms you described. I should add that, now eight weeks into the elimination diet, my lung capacity is nearly restored. I did not realize how impaired my lungs were until they came back!
Getting back to the PPIs, I found something else interesting as I tried to educate myself about this condition. I never had a headache in my life until doctors tried prescribing PPIs back in 2009 and 2010. They gave me crippling headaches, which is a possible side-effect. But even after stopping the PPIs, the headaches continued and got worse. In those individuals who are predisposed to food intolerance, acid-suppression therapy can cause full-blown symptoms, because the lack of stomach acid allows undigested protein molecules to pass into the small intestine where the damage begins. These molecules are sometimes called, "proteins with teeth."
There's much more I could write here, but I don't want to get on my soapbox! In four years I saw ten doctors, in private practice, a large university hospital, and even at the Mayo clinic -- and none of them mentioned diet, let alone food intolerance! When the autoimmune symptoms began snowballing, diagnoses ranged from andropause to hypothyroidism to brain tumor, and I endured many uncomfortable and expensive tests while continuing to suffer. Keep an open mind, and consider what I've shared.