In Europe it is actually very common practice to administer B12 shots for any nerve related pain (lumbar nerve pain, shingles , etc) and those have amazing effect. Now here in the USA it is "unheard of" tactic *sigh.
My husband had shingles flair 10 years ago and doctor was giving him all kind of meds with no effect and I insisted after 2 weeks of aginy to give him B12 shot or that I will find who will give him a shot and he got one - in TWO days shingles pain was literary gone ! Day one was 50% better, next day gone . BUT, I am sure that that same doctor never offered a B12 shot to any future patient.

B12 deficiency is actually common in older people because guts are getting older and absorbency is less efficient. For that reason it is better to take B12 tablets that are dissolved slowly under the tongue. That way vitamins are directly absorbed in bloodstream.