Vitamin B₁₂ deficiency causes impairment of normal DNA and fatty acid synthesis resulting in megaloblastic anemia, loss of proprioception and vibration sense with sensory disturbance.

MR imaging findings of subacute combined-degeneration of the cord is of long-segment, bilateral T2 hyperintensity of the dorsal columns giving rise to an “inverted V” or “rabbit-ear” appearance. In severe cases, signal abnormality can extend proximally to involve the brainstem and cerebellum.

Causes of B₁₂ deficiency include pernicious anemia, ileal or gastric fundal resection and a severely restricted diet.

Copper deficiency, most commonly related to reduced absorption after gastric surgery, can cause an indistinguishable clinicoradiological appearance.

Nitrous oxide administration can provoke symptomatic B₁₂ deficiency in patients with previously subclinical deficiency due to its action in oxidising active cobalamin into its inactive form.