Merck Manual

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Subacute Combined Degeneration


Michael Rubin

, MDCM, New York Presbyterian Hospital-Cornell Medical Center

Reviewed/Revised Feb 2023

Subacute combined degeneration is progressive degeneration of the spinal cord due to vitamin B12 deficiency.

  • Nerve fibers that control movement and sensation are damaged.

  • People have general weakness, tingling and numbness in the hands and feet, and stiff limbs and may become irritable, drowsy, and confused.

  • Blood tests can confirm vitamin B12 deficiency.

  • Vitamin B12, if promptly given by injection or by mouth, usually results in complete recovery.

Subacute combined degeneration usually affects people older than 40.

It is due to a deficiency of vitamin B12 Vitamin B12 Deficiency Vitamin B12 deficiency can occur in vegans who do not take supplements or as a result of an absorption disorder. Anemia develops, causing paleness, weakness, fatigue, and, if severe, shortness... read more , which usually also causes anemia. Pernicious anemia is a type of anemia that is due to a vitamin B12 deficiency. It is not related to diet but to the body's inability to absorb vitamin B12.

Vitamin B12 is necessary for the formation and maintenance of a fatty sheath (myelin sheath) that surrounds some nerve cells and that speeds transmission of nerve signals. In subacute combined degeneration, the myelin is damaged, causing sensory and motor nerve fibers from the spinal cord to degenerate. The brain, nerves of the eyes, and peripheral nerves are sometimes also damaged.

Symptoms of Subacute Combined Degeneration

Subacute combined degeneration begins with a general feeling of weakness. Tingling, a pins-and-needles sensation, and numbness are felt in both hands and feet. These sensations tend to be constant and to gradually worsen. People may not be able to feel vibrations and may lose the sense of where their limbs are (position sense). The limbs feel stiff, movements become clumsy, and walking may become difficult. Reflexes may be decreased, increased, or absent.

Rarely, vision is reduced.

People who have this disorder may become irritable, apathetic, drowsy, suspicious, and confused. Their emotions may change rapidly and unpredictably. Rarely, dementia develops.

Diagnosis of Subacute Combined Degeneration

  • Blood tests

  • Computed tomography (CT) or magnetic resonance imagine (MRI)

Blood tests to measure levels of vitamin B12 can confirm the deficiency. CT or MRI is done to rule out other causes of the symptoms.

Treatment of Subacute Combined Degeneration

  • Injections of vitamin B12

Recovery is more likely if subacute combined degeneration is treated early. When treated within a few weeks after symptoms appear, most people recover completely. If treatment is delayed, the progression of symptoms may be slowed or stopped, but full recovery of lost function is less likely.

Most people are immediately given injections of vitamin B12, which are continued indefinitely to prevent symptoms from recurring. Large doses of vitamin B12 taken by mouth can be used if vitamin B12 deficiency is mild and symptoms of nerve damage have not developed.

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