It was an exhaustively researched...shot in the dark.
You see, my husband was going down the tubes at the same time, but with totally different symptoms. The docs basically sent him home to die after his second acute pancreatitis attack in two months, fatty liver (this is a guy who never touched alcohol) constant dizziness, personality change, screaming pain in practically every muscle of his body, constant exhaustion, heart problems, high cholesterol, pre-diabetes, stalled digestive system...in short, a mess. I decided I had nothing to lose by searching for similar case studies for each of them on PubMed and then do a cross reference against my family's present symptoms and known medical histories. It took me about three months of 24/7 research to get to a "bottom line" of pernicious anemia. I had to twist my GP's arm somewhat to write a script for the shots, but for my husband at least, they worked immediately. I had to dig some more until I discovered that my son's extensive neuro damage required huge amounts of "hydroxocobalamin" and NOT the "cyanocobalamin" I was given by my GP. I wish I had found those links I posted when I was going through that . I discovered them just recently!
It was shocking to realize how clueless most doctors are about the symptoms and treatment of B12 deficiency. The same applies to neurologists (who should know better) and especially psychiatrists.
There's an outstanding book by Sally Pacholok R.N., and Jeffrey Stuart M.D. which you can get as an e-book on Amazon which IMHO every parent should read called, "Whats Wrong With My Child?"
I must warn you however - after you read that book, you won't sleep for a week!