I would get a B12 level run, ASAP. Nexium can block absorption of B12 (and some other nutrients--folic acid, iron, calcium,
zinc and magnesium).

When B12 gets low there are neuro symptoms, some may mimic MS.

His level should be 500 or more to be normal. USA labs still report very low levels like 150-200 as normal and they are not.

We have many threads on B12 at the Vitamin forum here and at PN.
Here is the information thread I made on PN:
http://neurotalk.psychcentral.com/thread85103.html

Some people have other reasons for B12 to fail. One is failure of intrinsic factor to be made in the stomach (which binds B12 from food) and this can be hereditary.
The other is from malabsorption, which is caused by a food intolerance called Gluten intolerance. Other inflammatory conditions in the intestines can be a factor too, like Crohn's.
Some drugs block B12, like metformin, for example.

You really need to read up on this. It is easy to fix, and most likely will need supplements for life. Oral works as well as
injections, and it is very inexpensive.