So much for THAT theory.It says 4.100 mmol/L and the range for normal is 3.500 - 5.800 mmol/L? I believe
What is his potassium level? Do you have copies of his bloodwork? Low potassium causes them to walk on their "hocks" , general weakness, can cause lethary, constipation, twitches, a stiff neck, even hoarseness.
Why does your wife suspect a brain tumor? just a gut feeling?
BTW, our Vet told us that pretty much all cats have a small amount of crystals in their urine. Said this was normal. .