Subacute combined degeneration
Subacute combined degeneration of the spinal cord; SCDSubacute combined degeneration (SCD) is a disorder of the spine, brain, and nerves. It causes weakness, abnormal sensations, mental problems, and vision difficulties.
Abnormal sensations
Numbness and tingling are abnormal sensations that can occur anywhere in your body, but they are often felt in your fingers, hands, feet, arms, or le...
Vision difficulties
There are many types of eye problems and vision disturbances, such as: Halos Blurred vision (the loss of sharpness of vision and the inability to see...
Causes
SCD is caused by vitamin B12 deficiency. It mainly affects the spinal cord. But its effects on the brain and the peripheral (body) nerves are the reason for the term "combined." At first, the nerve covering (myelin sheath) is damaged. Later, the entire nerve cell is affected.
Doctors do not know exactly how a lack of vitamin B12 damages the nerves. It is possible that the lack of this vitamin causes abnormal fatty acids to form around cells and nerves.
People are at high risk for this condition if vitamin B12 cannot be absorbed from their intestine or if they have:
- Pernicious anemia, a condition in which the body does not have enough healthy red blood cells due to vitamin B12 deficiency
Pernicious anemia
Anemia is a condition in which the body does not have enough healthy red blood cells. Red blood cells provide oxygen to body tissues. There are man...
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Crohn disease
Crohn disease is a disease where parts of the digestive tract become inflamed. It most often involves the lower end of the small intestine and the be...
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- Use of nitrous oxide (laughing gas), especially if used as a recreational drug
Symptoms
Symptoms include:
- Abnormal sensations (tingling and numbness)
- Weakness of the legs, arms, or other areas
These symptoms slowly get worse and are usually felt on both sides of the body.
As the disease worsens, symptoms may include any of the following:
- Clumsiness, stiff or awkward movements.
Clumsiness
Uncoordinated movement is due to a muscle control problem that causes an inability to coordinate movements. It leads to a jerky, unsteady, to-and-fr...
Read Article Now Book Mark Article - Mental changes, which can range from mild memory problems, irritability, apathy, and confusion, to severe dementia and psychosis. Severe dementia is uncommon, but in some cases it's the first symptom of the disorder.
Dementia
Dementia is a loss of brain function that occurs with certain diseases. It affects one or more brain functions such as memory, thinking, language, j...
ImageRead Article Now Book Mark Article - Decreased vision.
- Depression.
Depression
Depression may be described as feeling sad, blue, unhappy, miserable, or down in the dumps. Most of us feel this way at one time or another for shor...
ImageRead Article Now Book Mark Article - Sleepiness.
- Unsteady gait and loss of balance.
Unsteady gait
Walking abnormalities can be caused by many different types of problems. Problems with the joints, (such as arthritis), bones (such as deformities),...
ImageRead Article Now Book Mark Article - Falls due to poor balance.
Exams and Tests
Your health care provider will perform a physical exam. The exam usually shows muscle weakness and sensation problems on both sides of the body, especially in the legs. Knee jerk reflexes are often decreased or lost. Muscles may have spasticity. There may be reduced senses of touch, pain, and temperature.
Spasticity
Spasticity is stiff or rigid muscles. It may also be called unusual tightness or increased muscle tone. Reflexes (for example, a knee-jerk reflex) ...
Tests may be needed to determine why you are deficient in vitamin B12.
Nerve conduction studies and electromyography may be done to test for nerve damage in the extremities.
An eye exam may show damage to the optic nerve, a condition called optic neuropathy. There may also be abnormal pupil responses, loss of sharp vision, and other changes.
Optic neuropathy
Optic nerve atrophy is damage to the optic nerve. The optic nerve carries images of what the eye sees to the brain.
Blood tests that may be ordered include:
- Complete blood count (CBC)
Complete blood count (CBC)
A complete blood count (CBC) test measures the following:The number of white blood cells (WBC count)The number of red blood cells (RBC count)The numb...
ImageRead Article Now Book Mark Article - Vitamin B12 blood level
Vitamin B12 blood level
The vitamin B12 level is a blood test that measures how much vitamin B12 is in your blood.
Read Article Now Book Mark Article - Methylmalonic acid and homocysteine blood level
Methylmalonic acid and homocysteine blo...
The methylmalonic acid blood test measures the amount of methylmalonic acid in the blood.
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Treatment
Vitamin B12 is given, usually by injection into a muscle. Injections are often given once a day for a week, then weekly for about 1 month, and then monthly. Vitamin B12 supplements, either by injection or high-dose pills, must continue throughout life to prevent symptoms from returning.
Outlook (Prognosis)
Early treatment improves the chance of a good outcome.
How well a person does depends on how long they had symptoms before receiving treatment. If treatment is received within a few weeks, complete recovery may be expected. If treatment is delayed for longer than 1 or 2 months, full recovery may not be possible.
Untreated, SCD results in continued and permanent damage to the nervous system.
When to Contact a Medical Professional
Contact your provider if abnormal sensations, muscle weakness, or other symptoms of SCD develop. This is particularly important if you or a family member has had pernicious anemia or other risk factors.
Prevention
Some vegetarian diets, especially vegan, may be low in vitamin B12. Taking a supplement can help prevent SCD.
References
Pytel P, Anthony DC. Peripheral nerves and skeletal muscles. In: Kumar V, Abbas AK, Aster JC, eds. Robbins and Cotran Pathologic Basis of Disease. 10th ed. Philadelphia, PA: Elsevier; 2021:chap 27.
So YT. Deficiency diseases of the nervous system. In: Jankovic J, Mazziotta JC, Pomeroy SL, Newman NJ, eds. Bradley and Daroff's Neurology in Clinical Practice. 8th ed. Philadelphia, PA: Elsevier; 2022:chap 85.
Central nervous system and peripheral nervous system - illustration
The central nervous system comprises the brain and spinal cord. The peripheral nervous system includes nerves outside the brain and spinal cord.
Central nervous system and peripheral nervous system
illustration
Central nervous system - illustration
The central nervous system is made up of the brain and spinal cord. The brain functions to receive nerve impulses from the spinal cord and cranial nerves. The spinal cord contains the nerves that carry messages between the brain and the body. Spinal cord injury can occur when there is damage to the cells within the spinal cord or when the tracts of nerves that run up and down the spinal cord are severed.
Central nervous system
illustration
Central nervous system and peripheral nervous system - illustration
The central nervous system comprises the brain and spinal cord. The peripheral nervous system includes nerves outside the brain and spinal cord.
Central nervous system and peripheral nervous system
illustration
Central nervous system - illustration
The central nervous system is made up of the brain and spinal cord. The brain functions to receive nerve impulses from the spinal cord and cranial nerves. The spinal cord contains the nerves that carry messages between the brain and the body. Spinal cord injury can occur when there is damage to the cells within the spinal cord or when the tracts of nerves that run up and down the spinal cord are severed.
Central nervous system
illustration
Review Date: 4/29/2023
Reviewed By: Joseph V. Campellone, MD, Department of Neurology, Cooper Medical School of Rowan University, Camden, NJ. Review provided by VeriMed Healthcare Network. Also reviewed by David C. Dugdale, MD, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.
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