A 50-year-old man was initially seen with a 2-month history of bilateral lower extremity paresthesias and electric shock–like sensations with neck flexion (Lhermitte sign). He had maintained a strict vegetarian (vegan) diet for more than 15 years. Examination revealed markedly impaired lower extremity vibratory and joint-position sensation, with relative preservation of pain and temperature. Strength and reflexes were normal. The serum vitamin B12 level was less than 50 pg/mL (37 pmol/L) (reference range, 211-911 pg/mL [156-672 pmol/L]). Test results for antiparietal cell and anti-intrinsic factor antibodies were negative. Three months after the initiation of intramuscular repletion, the patient's vitamin B12 level had normalized and his symptoms had partially resolved.
Nakamura K, Mukherjee P, Swanson RA. Vitamin B12 Deficiency. Arch Neurol. 2004;61(6):960. doi:10.1001/archneur.61.6.960