I get quite a lot of patients with low B12, usually without any neuropsychiatric complication and would treat. I don't think there is any value in doing a Schilling test these days given that I always give B12 IM so its irrelevant. I will usually check anti-IF and anti-parietal cell antibodies if i'm thinking pernicious anemia.
B12 deficiency isn't usually rocket science, and I don't think medicine need to be involved unless you think the cause is Yersinia or Diphylobothrium latum infection etc.
The one thing I see here is alot of psychiatrists only order B12 and not folate. Folate deficiency can cause dementia too, and if you are getting a low B12 you need to know the folate, as treating low B12 but not low folate can precipitate subacute combined degeneration of the spinal cord.
The other thing is to check the K+ with the repeat B12 injections as you get massive red cell production which causes hypokalemia, sometimes significant which needs to be corrected.
The other thing to mention is B12 deficiency is rarely a 'reversible cause' of dementia. I have never seen giving B12 improve someone's cognitive function significantly and am told by the geriatricians the aim is more to prevent further cognitive decline and you rarely get improvement
Ok, first, let's say we are working in an impoverished African country with very limited health care resources and we can't waste anything. Also we have one internist and one psychiatrist and they keep a strict eye on expenses, and stay within their realms of expertise.
Second, I thought it was the reverse of what you're saying--that if you give only folate to a person who's deficient in both folate and B12, that the anemia corrects but the B12-related neurological damage continues. That's how folate repletion alone can mask B12 deficiency--is that correct?
IF that's correct, and
if the patient
has dementia, you can just check B12. If it's
normal, then stop there and look for a different cause of dementia. If it's low, then check an MCV. If that's normal, stop, assume it's low B12 with normal folate, and just treat the B12. If the MCV is high, then check folate. If that's low, then replete both folate and B12. Because if you are going to treat the dementia you should do the patient a favor and also treat the anemia, and just giving B12 won't correct the anemia if both are low. Although the only reason I can think of why someone would be low in both would be malnutrition, and you should be treating that anyway regardless of dementia.
The problem with B12 deficiency in psychiatry is that we start by seeing the dementia, rather than the macrocytic anemia. Once you've determined that low B12 is causing dementia, you're kind of obligated to look for and treat the anemia. But technically, that is not psychiatry.
In fact, if the problem is
only anemia and
no dementia, then we shouldn't even know about the problem.
Now, in our patient with dementia who turns out to have low B12, knowing the reason seems important to me--so back to the Schilling test. If the cause is pernicious anemia, then the treatment would be different than if it's just poor diet. You might need a higher dose or an IM formulation. Since supplies are limited, we want to correctly identify these people.
I know B12 deficiency is not very complicated and we in psychiatry could certainly handle it assuming there's no schilling test. But just as a matter of principal I was saying I'd send a patient with low B12 and no neuropsych sx to medicine because it falls in their realm in that case.
In real life I would not do any of this of course.
