Severe vitamin B12 deficiency can occur with normal blood levels of B12

Vitamin B12 deficiency is common in the elderly, vegetarians, people with diabetes, and other chronic conditions. This deficiency can cause neurological, psychiatric, hematological, and other symptoms. It can be a contributing factor to migraines, especially in people who experience visual auras.

If not treated, vitamin B12 deficiency can cause dementia, spinal cord damage, loss of vision, and permanent nerve damage. I check vitamin B12 levels in all of my patients. The blood test, however, is not always reliable. There are reports of severe deficiency with perfectly normal levels. This is why when a deficiency is suspected, additional tests are needed. These are homocysteine and methylmalonic acid levels. These tests can disclose the presence of a deficiency when vitamin B12 level is in the normal range.

To further complicate matters, a report by neurologists at UCSF described a patient with normal blood tests who nevertheless had a severe vitamin B12 deficiency in the brain. They discovered that this patient had antibodies to a receptor (CD320) that is necessary for the uptake of vitamin B12 from the blood into the brain across the blood-brain barrier. The spinal fluid of this patient completely lacked vitamin B12. Her presenting symptoms were difficulty speaking, unsteadiness, and tremor. She had no peripheral manifestations of vitamin B12 deficiency, only those related to the brain. She recovered with high doses of vitamin B12 supplementation and immunosuppressive therapy to reduce the amount of antibodies against the CD320 receptor.

The authors screened a few hundred patients with lupus, multiple sclerosis, and healthy controls. They found these antibodies in 6% of healthy controls, 6% of those with lupus without neurological symptoms, and 6% with multiple sclerosis. Antibodies were present in 21% of patients with lupus who had neurological symptoms.

This newly described condition is called autoimmune B12 central deficiency (ABCD). The role of these antibodies in healthy people is not clear. However, people with unexplained neurological symptoms should have a blood test for homocysteine, methylmalonic acid, and CD320 antibodies.