General description

Vitamin B12 deficiency

Since the body cannot synthesize vitamin B12, it must be obtained from the diet. Dietary vitamin B12 binds to intrinsic factor, a glycoprotein produced by gastric parietal cells, allowing absorption in the distal ileum. Once absorbed, vitamin B12 enters the bloodstream, binds to transcobalamin, and is transported to the liver and other tissues.

The most common cause of vitamin B12 deficiency is malabsorption, often due to conditions like pernicious anemia, where an autoimmune process damages gastric parietal cells, reducing intrinsic factor production. Other causes include gastric resection, ileal disease, bacterial overgrowth syndrome, where bacteria consume vitamin B12 before it is absorbed, parasitic infections like tapeworm, and exposure to nitrous oxide, which deactivates vitamin B12.

Subacute combined degeneration of spinal cord (SCD)

Subacute combined degeneration of spinal cord (SCD) is a neurological disorder caused by vitamin B12 (cobalamin) deficiency, leading to degeneration in the posterior and lateral columns of the spinal cord.

SCD typically has a gradual onset, presenting first with symmetrical tingling and numbness in the hands and feet, often more severe in the legs (glove-and-stocking pattern). Over weeks to months, patients may experience deep sensory loss, muscle weakness, spasticity, and difficulty walking due to early involvement of the posterior columns, resulting in ataxia. As the condition progresses, symptoms may include visual disturbances, mental status changes, bilateral spastic paresis, reduced sensitivity to pressure, vibration, and touch, and a positive Babinski sign. Severe, prolonged B12 deficiency can lead to irreversible nervous system damage, making early diagnosis and treatment crucial.

Leukoencephalopathy associated with cobalamin deficiency

Vitamin B12 deficiency can sometimes lead to extensive white matter lesions, resulting in cognitive impairment, pyramidal tract symptoms, sensory disturbances, and visual impairment. In some cases, involuntary movements may also occur.