Nerve root disorders result from sudden or long-term pressure on the spinal nerve root.
Nerve root disorders usually result from a herniated disk or osteoarthritis in the spine.
These disorders can cause pain, abnormal sensations, and/or muscle weakness in the area of the body they supply.
Doctors diagnose nerve root disorders based on results of imaging tests, electrodiagnostic testing, and tests to identify the cause.
(See also Overview of Peripheral Nervous System Disorders.)
Nerve roots are the short branches of a spinal nerve. Spinal nerves exit the spinal cord along the length of the spine. Each spinal nerve contains two nerve roots: one motor and one sensory. (Motor nerve roots contain nerve fibers that carry commands from the brain and spinal cord to muscles. Sensory nerve roots contains nerve fibers that carry sensory information about such things as touch, position, pain, and temperature from the body to the spinal cord.) After exiting the spinal cord, the two nerve roots join to form a single spinal nerve. Each spinal nerve then goes between two back bones (vertebrae) in the spine to connect to a specific area of the body. The surface of the skin is divided based on these specific areas, which are called dermatomes. A dermatome is an area of skin whose sensory nerves all come from a single spinal nerve root.
The Spine
A column of bones called vertebrae make up the spine (spinal column). The vertebrae protect the spinal cord (a long, fragile structure contained in the spinal canal), which runs through the center of the spine. Between the vertebrae are disks composed of cartilage, which help cushion the spine and give it some flexibility. Spinal nerves: Emerging from the spinal cord between the vertebrae are 31 pairs of spinal nerves. Each nerve emerges in two short branches (roots)—motor and sensory—which join to form a spinal nerve. The motor roots carry commands from the brain and spinal cord to other parts of the body, particularly to skeletal muscles. The sensory roots carry information to the brain from other parts of the body. Cauda equina: The spinal cord ends about three fourths of the way down the spine, but a bundle of nerves extends beyond the cord. This bundle is called the cauda equina because it resembles a horse's tail. The cauda equina carries nerve impulses to and from the legs, lower intestine, and bladder. |
Dermatomes
The surface of the skin is divided into specific areas, called dermatomes. A dermatome is an area of skin whose sensory nerves all come from a single spinal nerve root. Sensory nerves carry information about such things as touch, pain, temperature, and vibration from the skin to the spinal cord. Spinal roots come in pairs—one of each pair on each side of the body. There are 31 pairs:
There are dermatomes for each of these nerve roots. Sensory information from a specific dermatome is carried by sensory nerve fibers to the spinal nerve root of a specific vertebra. For example, sensory information from a strip of skin along the back of the thigh, is carried by sensory nerve fibers to the 2nd sacral vertebra (S2) nerve root. |
Causes of Nerve Root Disorders
The most common cause of nerve root disorders is
A herniated disk can cause a nerve root disorder by putting pressure on the nerve root next to it.
Rheumatoid arthritis (RA) or osteoarthritis can cause changes in the spine that put pressure on (compress) nerve roots, especially in the neck and lower back. In osteoarthritis, bone in the spine can overgrow and narrow the opening between the vertebrae that the nerve root goes through.
Less commonly, a tumor or other mass (such as an abscess) puts pressure on a nerve root.
Diabetes mellitus can cause a nerve root disorder by damaging blood vessels that provide blood to the nerve root.
Infections, such as tuberculosis (TB), Lyme disease, syphilis, and shingles, sometimes affect nerve roots.
Symptoms of Nerve Root Disorders
Symptoms of nerve root disorders depend on which nerve root is affected. Pain, abnormal sensations, and/or muscle weakness occur in the area of the body supplied by the nerve root. The pain may feel like an electric shock that radiates through the affected area. Muscles may waste away and/or twitch. Affected muscles may become paralyzed.
Pain may be worsened by movement, including moving the back, coughing, and sneezing.
If the lowest roots of the spinal cord (the cauda equina) are affected, people may have weakness in the legs, urinary problems (such as incontinence or retention of urine), lose control of their bowels, and lose sensation in the buttocks, genital area, bladder, and rectum. Men may have trouble having an erection. This disorder, called cauda equina syndrome, is a medical emergency. The problem—such as a herniated disk, an abscess, a tumor, or a blood clot—that is putting pressure on the cauda equina must be corrected to prevent permanent nerve damage.
Diagnosis of Nerve Root Disorders
Imaging tests
Sometimes electrodiagnostic tests
Doctors ask about symptoms and do a physical examination. The findings provide clues to the diagnosis and help doctors determine where the problem is.
Magnetic resonance imaging (MRI) or computed tomography (CT) is done to confirm the diagnosis. MRI shows the spinal cord, as well as abnormalities in the soft tissues around the cord, such as abscesses, hematomas (collections of blood), tumors, and ruptured disks, and in bone, such as tumors, fractures, osteoarthritis, and cervical spondylosis.
If MRI cannot be done and if results of CT are unclear, myelography is done. For myelography, a radiopaque contrast agent (which can be seen on x-rays) is injected into the space around the spinal cord, and x-rays are taken. CT myelography may also be done. CT myelography can provide detailed images of the spinal cord and surrounding bone.
Electrodiagnostic tests (electromyography and nerve conduction studies) are done to identify which nerve roots are damaged and to confirm that symptoms are caused by compression of the spinal nerve rather than by problems in the spinal cord or in a nerve plexus (a network of nerve fibers, where fibers from different spinal nerves are sorted and recombined to serve a particular area of the body). However, these tests cannot always identify the cause.
If imaging tests do not identify a cause, a spinal tap is done, and doctors analyze the fluid that surrounds the brain and spinal cord (cerebrospinal fluid) to check for infections. Doctors also measure the blood glucose level after people have fasted to check for diabetes and may do other tests depending on the suspected cause.
Treatment of Nerve Root Disorders
Treatment of the cause
Treatment of pain
Surgery (usually as a last resort)
Causes of nerve root disorders are treated when possible.
For sudden, immediate pain, non-opioid pain relievers (analgesics)
For long-lasting (chronic) painOpioid pain relievers have a risk of addiction. Some antidepressants and antiseizure medications, which are usually not considered pain relievers, can lessen pain due to nerve damage. Physical therapy may also help relieve pain. If all of these treatments are ineffective, some people may wish to try alternative medicine (such as transdermal electrical nerve stimulation, chiropractic, acupuncture, or medicinal herbs).
If the pain is unrelenting or if pressure on spinal nerves is causing muscle weakness or loss of sensation, surgery to relieve the pressure may be necessary. If compression of the cauda equina or the spinal cord causes urinary or fecal incontinence, surgery is usually necessary and is done promptly to prevent permanent damage.
