Definition of Subacute combined degeneration:

Subacute combined degeneration of the spinal cord is a disorder that involves weakness, abnormal sensations, mental problems, and vision difficulties.

Causes, incidence, and risk factors:

Subacute combined degeneration of the spinal cord is caused by a vitamin B12 deficiency. (For specific information on vitamin B12 deficiency, see the article on pernicious anemia.)

Subacute combined degeneration primarily affects the spinal cord, but it can also damage the brain, the nerves of the eye, and the peripheral (body) nerves. At first, the disease damages the covering of the nerves (the myelin sheath), which speeds nerve signaling. It later affects the entire nerve cell.

How a lack of vitamin B12 damages nerves is unclear. However, experts believe the lack of this vitamin causes abnormal fatty acids to form around cells and nerves.

You have a higher risk for this condition if you cannot absorb vitamin B12 from the intestines or if you have:

• Pernicious anemia
• Disorders of the small intestine, including Crohn's disease
• Malabsorptive conditions, which can occur after gastrointestinal surgery