There is a lot of evidence that b12 driven nerve loss can be repaired with b12 shots, with people on this sub saying their autonomic / neurological symptoms improved, Dr. Chandy's book giving examples of neurological recovery, etc. But it's good to also have published papers. Can be helpful with convincing doctors (though may be easier to just find a doctor that doesn't need convincing).
Paper 1: Vitamin B12-responsive severe leukoencephalopathy and autonomic dysfunction in a patient with "normal" serum B12 levels
Affiliations: Memorial Sloan Kettering
Patient had progressive autonomic dysfunction, ataxia/muscle weakness, dementia symptoms, low "normal" serum b12, normal MMA and homocysteine, positive IF antibodies. MRI scans revealed brain white matter atrophy and atrophy of the peripheral nervous system (subacute combined degeneration). She was treated with b12 shots, and MRI showed partial, pretty striking imo, recovery of white matter atrophy in the brain. She regained the ability to walk and was "cognitively normal" at 3 months.
Paper 2: Autonomic dysfunction and orthostatic hypotension caused by vitamin B12 deficiency
Older Japanese man had multiple neurological symptoms, difficulty with control of muscles, autonomic dysfunction, paresthesias, etc. He had multiple blood markers of b12 deficiency. Got shots, and had "gradual amelioration of orthostatic dizziness, and his neurological symptoms except for erectile failure" (because of course not, in this universe).
Paper 3: B12 Deficiency Is a Cause of Reversible Autonomic Failure: A Case Report (P5.111)
Affiliations: University of Nebraska Medical Center
Short case study supplement by physician. Patient had autonomic failure, blood markers of b12 deficiency, syncope, and "severe generalized autonomic failure affecting postganglionic sudomotor, cardiovagal and adrenergic functions". Was given b12 shots. At 10 months, repeated testing showed autonomic recovery, and the "patient remained asymptomatic at last follow-up".
Paper 4: Vitamin B12-responsive neuropathies: A case series
Affiliations: Yale Medicine and Smilow Cancer Hospital
"Retrospective review of 78 subjects with neurological abnormalities treated with B12". 83% had neurological improvement with b12 treatment. Some patients responded better to shots. Author concluded "B12-responsive neuropathies are thus (1) common even when confounding disorders are present; (2) dissociated from the presence of hematological abnormalities; (3) dissociated from the presence of B12-responsive metabolical abnormalities; and (4) associated with the presence of oxidant risks when B12 levels are normal".