Also affects dorsal and lateral columns of spinal cord--> myleopathy
Also affects cognitive function, bone marrow
Etiology
Pernicious anemia: an auto-immune process w/anti-bodies directed against the parietal cells--> decreased intrinsic factor--> impaired ability to absorb B12
S/p gastrectomy, w/loss of parietal cells
Malabsorption: crohn's dz, gastric by-pass, ileal resection (site of b12 absorption in small intestine)
Diet related (ie dont consume or have access to B12) or from meds that interfere w/absorption (e.g. PPI, H2 blockers); chronic metformin use; Nitrous oxide abuse ("whippets"), which inactivates B12
Symptoms
Gait problems
Fatigue
Sob w/anemia
Progressive numbness
Paresthesia which can be painful
Affects legs more common then arms
Symmetric weakness
Confusion/cognitive impairment
Physical Exam Findings
Ataxia
+ rhomberg
Tachycardia if sig anemia
Tongue can be smooth and swollen if severe
Diminished peripheral sensation
Impaired proprioception
Impaired vibration sense
Hyperreflexia (if myelopathy predominates) or hyporeflexia (if PN predominates)
Symmetric weakness
Tests
Low serum B12; elevated methylmalonic acid, homocysteine (less specific than MMA)
Sometimes macrocytosis, anemia, hyper-segmented PMNs; w/severe deficiency, can develop pancytopenia