Spinal cord injury

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Overview
Spinal cord injury causes myelopathy or damage to white matter or myelinated fiber tracts that carry sensation and motor signals to and from the brain. It also damages gray matter in the central part of the spinal, causing segmental losses of interneurons and motorneurons. Spinal cord injury can occur from many causes, including:
 * Trauma such as automobile accidents, falls, gunshots, diving accidents, war injuries, etc.
 * Tumor such as meningiomas, ependymomas, astrocytomas, and metastatic cancer.
 * Ischemia resulting from occlusion of spinal blood vessels, including dissecting aortic aneurisms, emboli, arteriosclerosis.
 * Developmental disorders, such as spina bifida, meningomyolcoele, and other.
 * Neurodegenerative diseases, such as Friedreich's ataxia, spinocerebellar ataxia, etc.
 * Demyelinative diseases, such as Multiple Sclerosis.
 * Transverse myelitis, resulting from spinal cord stroke, inflammation, or other causes.
 * Vascular malformations, such as arteriovenous malformation (AVM), dural arteriovenous fistula (AVF), spinal hemangioma, cavernous angioma and aneurysm.

Classification
The American Spinal Cord Injury Association or ASIA defined an international classification based on neurological levels, touch and pinprick sensations tested in each dermatome, and strength of ten key muscles on each side of the body, i.e. shoulder shrug (C4), elbow flexion (C5), wrist extension (C6), elbow extension (C7), hip flexion (L2), knee extension (L3), ankle dorsiflexion (L4), long toe extension (L5), and ankle plantar flexion (S1). Each muscle is graded on a scale of 0-5 where 0 is paralyzed, 1 is slight movement, 2 is definite movement, 3 is movement against gravity, 4 is movement against manual resistance, and 5 is normal. The scores of the muscles add up to 100. The pinprick and touch sensations are grade separately for each dermatome on a scale of 0-2 where 0 is absent sensation, 1 is abnormal sensation, and 2 is normal. These add up to 112 points each for pinprick and touch.

Traumatic spinal cord injury is classified into five types by the American Spinal Injury Association (ASIA) and the International Spinal Cord Injury Classification System.
 * A indicates a "complete" spinal cord injury where no motor or sensory function is preserved in the sacral segments S4-S5. A complete injury is one in which there is some neurological level below which there is no motor or sensory function.  Since the S4-S5 segment is the lower segmental, absence of motor and sensory function indicates "complete" spinal cord injury.
 * B indicates an "incomplete" spinal cord injury where sensory but not motor function is preserved below the neurological level and includes the sacral segments S4-S5. This is typically a transient phase and if the person recovers any motor function below the neurological level, that person essentially becomes a motor incomplete, i.e. ASIA C or D.
 * C indicates an "incomplete" spinal cord injury where motor function is preserved below the neurological level and more than half of key muscles below the neurological level have a muscle grade of less than 3.
 * D indicates an "incomplete" spinal cord injury where motor function is preserved below the neurological level and at least half of the key muscles below the neurological level have a muscle grade of 3 or more.
 * E indicates "normal" where motor and sensory scores are normal. Note that it is possible to have spinal cord injury and neurological deficit with completely normal motor and sensory scores.

In addition, there are several clinical syndromes associated with incomplete spinal cord injuries.
 * The Central Cord syndrome is associated with greater loss of upper limb function compared to lower limbs.
 * The Brown-Séquard syndrome results from injury to one side with the spinal cord, causing weakness and loss of proprioception on the side of the injury and loss of pain and thermal sensation of the other side.
 * The Anterior Spinal syndrome results from injury to the anterior part of the spinal cord, causing weakness and loss of pain and thermal sensations below the injury site but preservation of proprioception that is usually carried in the posterior part of the spinal cord.
 * Tabes Dorsalis results from injury to the posterior part of the spinal cord, usually from infection diseases such as syphilis, causing loss of touch and proprioceptive sensation.
 * Conus Medullaris syndrome results from injury to the tip of the spinal cord, located at L1 vertebra.
 * Cauda Equina syndrome is, strictly speaking, not really spinal cord injury but injury to the spinal roots below the L1 vertebra.

One can have spine injury without spinal cord injury. Many people suffer transient loss of function ("stingers") in sports accidents or pain in "whiplash" of the neck without neurological loss and relatively few of these suffer spinal cord injury sufficient to warrant hospitalization. In the United States, the incidence of spinal cord injury has been estimated to be about 35 cases per million per year, or approximately 10,500 per year (35 * 300). In China, the incidence of spinal cord injury was recently estimated to be as high as 65 cases per million per year in urban areas. If so, assuming a population of 1.3 billion, this would suggest an incidence of 84,500 per year (65 * 1300).

The prevalence of spinal cord injury is not well known in many large countries. In some countries, such as Sweden and Iceland, registries are available. About 450,000 people in the United States live with spinal cord injury (one in 670), and there are about 11,000 new spinal cord injuries every year (one in 30,000). The majority of them (78%) involve males between the ages of 16-30 and result from motor vehicle accidents (42%), violence (24%), or falls (27%).

The Effects of Spinal Cord Injury
The exact effects of a spinal cord injury vary according to the type and level injury, and can be organized into two types:
 * In a complete injury, there is no function below the "neurological" level, defined as the lowest level that has intact neurological function. If a person has some level below which there is no motor and sensory function, the injury is said to be "complete".  Recent evidence suggest that less than 5% of people with "complete" spinal cord injury recover locomotion.
 * A person with an incomplete injury retains some sensation or movement below the level of the injury. The lowest spinal cord level is S4-5, representing the anal sphincter and peri-anal sensation.  So, if a person is able to contract the anal sphincter voluntarily or is able to feel peri-anal pinprick or touch, the injury is said to be "incomplete".  Recent evidence suggest that over 95% of people with "incomplete" spinal cord injury recover some locomotory ability.

In addition to a loss of sensation and motor function below the point of injury, individuals with spinal cord injuries will often experience other complications of spinal cord injury:
 * Bowel and bladder function is regulated by the sacral region of the spine, so it is very common to experience dysfunction of the bowel and bladder, including infections of the bladder, and anal incontinence.
 * Sexual function is also associated with the sacral region, and is often affected.
 * Injuries of the C-1, C-2 will often result in a loss of breathing, necessitating mechanical ventilators or phrenic nerve pacing.
 * Inability or reduced ability to regulate heart rate, blood pressure), sweating and hence body temperature.
 * Spasticity (increased reflexes and stiffness of the limbs).
 * Neuropathic pain.
 * Autonomic dysreflexia or abnormal increases in blood pressure, sweating, and other autonomic responses to pain or sensory disturbances.
 * Atrophy of muscle.
 * Osteoporosis (loss of calcium) and bone degeneration.
 * Gallbladder and renal stones.

The Location of the Injury
Knowing the exact level of the injury on the spinal cord is important when predicting what parts of the body might be affected by paralysis and loss of function.

Below is a list of typical effects of spinal cord injury by location (refer to the spinal cord map to the right). Please keep in mind that while the prognosis of complete injuries are predictable, incomplete injuries are very variable and may differ from the descriptions below.

Cervical injuries
Cervical (neck) injuries usually result in full or partial tetraplegia. Depending on the exact location of the injury, one with a spinal cord injury at the cervical level may retain some amount of function as detailed below, but are otherwise completely paralyzed.


 * C3 vertebrae and above : Typically lose diaphragm function and require a ventilator to breathe.
 * C4 : May have some use of biceps and shoulders, but weaker'''
 * C5 : May retain the use of shoulders and biceps, but not of the wrists or hands.'''
 * C6 : Generally retain some wrist control, but no hand function.
 * C7 and T1 : Can usually straighten their arms but still may have dexterity problems with the hand and fingers. C7 is generally the level for functional independence.

Thoracic injuries
Injuries at the thoracic level and below result in paraplegia. The hands, arms, head, and breathing are usually not affected.


 * T1 to T8 : Most often have control of the hands, but lack control of the abdominal muscles so control of the trunk is difficult or impossible. Effects are less severe the lower the injury.
 * T9 to T12 : Allows good trunk and abdominal muscle control, and sitting balance is very good.

Lumbar and Sacral injuries
The effect of injuries to the lumbar or sacral region of the spinal canal are decreased control of the legs and hips, urinary system, and anus.

Central Cord and Other Syndromes


Central cord syndrome (picture 1) is a form of incomplete spinal cord injury characterized by impairment in the arms and hands and, to a lesser extent, in the legs. This is also referred to as inverse paraplegia, because the hands and arms are paralyzed while the legs and lower extremities work correctly.

Most often the damage is to the cervical or upper thoracic regions of the spinal cord, and characterized by weakness in the arms with relative sparing of the legs with variable sensory loss.

This condition is associated with ischemia, hemorrhage, or necrosis involving the central portions of the spinal cord (the large nerve fibers that carry information directly from the cerebral cortex). Corticospinal fibers destined for the legs are spared due to their more external location in the spinal cord.

This clinical pattern may emerge during recovery from spinal shock due to prolonged swelling around or near the vertebrae, causing pressures on the cord. The symptoms may be transient or permanent.

Anterior cord syndrome (picture 2) is also an incomplete spinal cord injury. Below the injury, motor function, pain sensation, and temperature sensation is lost; touch, proprioception (sense of position in space), and vibration sense remain intact. Posterior cord syndrome (not pictured) can also occur, but is very rare.

Brown-Séquard syndrome (picture 3) usually occurs when the spinal cord is hemisectioned or injured on the lateral side. On the ipsilateral side of the injury (same side), there is a loss of motor function, proprioception, vibration, and light touch. Contralaterally (opposite side of injury), there is a loss of pain, temperature, and deep touch sensations.

Treatment
Treatment for acute traumatic spinal cord injuries have consisted of giving high dose methylprednisolone if the injury occurred within 8 hours. The recommendation is primarily based on the National Acute Spinal Cord Injury Studies (NASCIS) II and III. Some of the claims of the studies have been challenged as being from faulty interpretation of the data.

Breakthrough medical research shows stem cell transplants could have the potential to help or cure paralysis caused by spinal injury. Stem cells are primal cells found in all multi-cellular organisms. They can be made to differentiate into a range of specialized cells including nerve cells, which can be transplanted into the body.

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