B12 deficiency

[An-S]

  Two years ago, I began receiving monthly 1000 mcg injections of B12 for severe
  symptoms (my dr. missed my "rock-bottom" B12 test results seven months
  earlier, and instead of injections, sent me to a counselor for "emotional
  healing"!).
  Two months ago, I was on erythromycin for an infection and experienced quite
  a few symptoms, including a numb tongue, palate and gums; liver problems,etc.
  The feeling in my mouth returned two weeks after completing the antibiotics.
  Three weeks ago, I began to experience the familiar muscle twitches,
  random numbness, eyesight problems, etc. associated with a B12 deficiency.
  Bloodwork has shown an above normal B12 level - yet an obvious
  megaloblastic anemia.
  First of all, could the antibiotic have caused another B12 crisis?
  Second, if I do have another B12 deficiency, will my neurological symptoms
  become permanent?  What about a folate deficiency - would that cause my
  B12 level to appear normal while being B12 anemic?
  Thank you.
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Dear Risa:
Megaloblastic anemia despite high vitamin B12 levels suggests one of the following possibilities: a disorder of vitamin B12 metabolism (rare), folate deficiency (malabsorption, malnutrition, alcoholism, some cancers and hematological states, pregnancy), disorder of folate metabolism (such as with some cancer drugs), or a primary disorder of the bone marrow (such as a myelodysplastic syndrome, which can even spuriously raise measured vit B12 levels). The precise diagnosis may require the involvement of a hematologist.
Your neurological symptoms can plausibly be a consequence of Vit B12 deficiency, but are not typical. An exposure to Erythromycin should not cause or unmask Vit B12 or even Folate deficiency (although some other antibiotics could potentially do the latter). Exposure to nitrous oxide (for surgery, or as a recreational agent) can unmask or even cause vitamin B12 deficiency, even in the presence of a normal B12 level.
It is a little difficult to answer your second question. The milder manifestations of B12 deficiency improve remarkbly well in 6 months or so.