Manish Sharma, M.B.B.S.
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The nervous system is a complex and wide-reaching network of nerve cells called neurons. Their connections, called synapses, reach all areas of the body. The nervous system receives and relays sensory information like vision, sound, smell, taste, touch and pain.
The nervous system is fragile. It can be damaged, and it heals with great difficulty, if at all. This affects the brain's ability to communicate with your muscles and sensory organs. Nervous system injuries can be painful, and cause weakness, tingling, numbness and even changes in blood circulation.
All the neurons in your body start and end in your brain or spinal cord. The brain and spinal cord make up the central nervous system, which is usually what first comes to mind for many people.
The peripheral nervous system, on the other hand, connects the central nervous system with your internal organs, muscles and sensory tissues. These nerves fire muscles; sense temperature; and control your heart, lungs and other involuntary functions essential to life. To put it simply, neurons are like electrical wires that are lined on the outside by special cells that provide insulation. Each neuron has a head called the cell body and a long tail called an axon. The head is connected to the spinal cord or brain, and the tail connects to a muscle or organ.
Central nervous system injuries
Injuries to the spinal cord or brain can happen in an instant. They can be caused by an auto accident, sports injury, fall, stroke, ruptured brain aneurysm, lack of oxygen, gunshots or an explosive blast. These injuries are often called traumatic brain injuries or traumatic spine injuries.
Injured nerve cells in the central nervous system typically do not regenerate. However, this part of the nervous system can reorganize in response to an injury. This is called "plasticity." Luckily, the brain has a lot of built-in redundancy. Simply put, when one area loses function, other undamaged areas of the brain can take over. For example, if a stroke causes an area of brain damage, other parts of the nervous system can take over the lost function of the damaged area. The chance of recovery is greatest in patients 40 and younger after a traumatic brain injury.
Neurosurgeons can't alter the primary injury suffered by the brain or spinal cord, but they can prevent secondary damage from occurring. Surgical procedures can relieve pressure on the spinal cord and brain. This prevents damage from progressing to other areas.
Peripheral nervous system injuries
Injuries to the peripheral nervous system can happen slowly over time or in an instant. Accidents, falls and sports can cause injuries. Repetitive microtrauma, such as carpal tunnel syndrome, also can cause nerve damage. Other causes of nerve injury include diabetes, radiation, alcoholism, viral illnesses, birth trauma, surgery, autoimmune reactions and certain hereditary conditions.
Three types of peripheral nervous system injuries are:
This is the mildest and most common type of nerve injury. The nerve itself is intact and merely stunned. Any resulting numbness, weakness or loss of function is temporary, and most people make nearly a complete recovery with rest and time. Surgery is rarely needed.
This is a partial nerve injury. The outer nerve sheath is intact, but the neurons within are damaged. Nerve cells can regenerate and grow back at a rate of about an inch a month, but recovery is typically incomplete and slow.
This is a complete nerve injury, where the nerve sheath and underlying neurons are severed. If there is an open cut, a neurosurgeon can see the cut nerve ends at surgery and repair this. If the gap is less than 2 centimeters, the nerve ends may be sutured together, provided they come together easily. Larger gaps may need artificial conduits or nerve grafts to fill the defect. Surgery is almost always needed.
Stretch injuries are the most encountered pattern of nerve damage. These may result from a fall, a birth injury, a motor vehicle accident, a surgical procedure or workplace injury. All three types of nerve injuries detailed above also can occur or in combination with one another. Most people improve within three to six months, but surgery may be needed based on the lack of clinical improvement and other tests, including an ultrasound and electromyography.
The chance of nerve regeneration is greater within the peripheral nervous system. This is because these neurons have a different lining, or sheath, made up of Schwann cells. The central nervous system does not have these cells. Schwann cells can help damaged nerves regenerate and restore function. On average, damaged nerves can grow back at a rate of about 1 inch per month or 1 millimeter per day.
Surgery is needed if there is significant scar tissue or a gap between cut nerve ends. Neurolysis is a surgical procedure that removes scar tissue from around and sometimes from within the nerve to improve its function. Direct nerve repair or primary neurorrhaphy involves suturing cut nerve ends together with ultrafine sutures or glue. Nerve grafting repairs larger gaps that are bridged with nerves harvested typically from the patient's leg, cadaver nerves or synthetic conduits that may be lined with biological factors to enhance nerve regeneration.
Neurotization or nerve transfers involve sacrificing a healthy nerve by severing it and using it as a source of neurons to hot-wire a more important damaged nerve close to its entry into the paralyzed muscle. This bypasses scarring at the level of injury and reduces the time taken to reenergize the muscle. A neurosurgeon can use one or more procedures to repair damaged nerves.
Nerve surgery isn't right for every patient. These procedures are most successful in younger patients who are in good overall health. Patients who are obese; smoke; or have diabetes, poor circulation or undergone radiation therapy previously fare worse.
Complex regional pain syndrome
This is a rare but severe form of chronic pain that affects a limb. The pain is out of proportion to the severity of the initial injury.
Type 1 complex regional pain syndrome may occur after an injury that did not directly damage the limb or nerves therein, such as after a stroke or heart attack. Type 2 complex regional pain syndrome occurs after a crush injury to a limb and direct nerve damage there. This poorly understood condition likely involves inflammation and hypersensitivity at the level of the peripheral and central nervous systems.
Symptoms include extreme burning or throbbing pain, sensitivity to touch, changes in skin color, skin temperature and swelling. Physicians aren't sure why this occurs in some people and not others. A multidisciplinary team of health care professionals is needed to treat this rare and agonizing condition.
Peripheral nerve injuries can be treated nonoperatively with rest, physical therapy, desensitization techniques and medications to numb the pain while allowing the nerve to grow back. Surgical procedures have evolved over the years and produce excellent results in carefully selected patients with paralyzed muscles, pain, numbness and lost function.