Nerve Conduction Study

A medical diagnostic tool used to evaluate the ability of the motor and sensory nerves for electrical conduction is the Nerve conduction study. Nerve conduction studies are performed by medical specialists in neurophysiology, physiatry and neurology with sub-specialization in electro diagnostic medicine. The common measurement made during this test is called Nerve conduction velocity or NCV. This is conducted to determine the damage and destruction caused to nerves.

Procedure

The procedure is to stimulate the nerve with surface electrode patches attached to the skin. Two electrodes are placed on the skin over the nerve. One electrode stimulates the nerve with a mild electrical impulse. The resulting electrical activity is recorded by another electrode. This testing is repeated in about 2 - 3 places along the arms or legs. After the procedure, the nerve conduction speed is calculated by measuring the distance between electrodes and the time it takes for electrical impulses to travel between electrodes.

The nerve conduction velocity (speed) is then calculated by measuring the distance between electrodes and the time it takes for electrical impulses to travel between electrodes.

A related procedure that may be performed is electromyography (EMG). An EMG measures the electrical activity in muscles and is often performed at the same time as NCS. Both procedures help to detect the presence, location and extent of diseases that damage the nerves and muscles.

Prior to the procedure

This study does not require any fasting or sedation prior to the procedure. But body temperature must be maintained before and during the procedure as low body temperature slows nerve conduction. Keep the doctor informed in case of any medicine or herbal supplements you might be taking. You must stop using lotions or oils on your skin a few days before the procedure. Based on your medical condition, the doctor may request any other specific preparation.

During the procedure

A nerve conduction study is performed as an outpatient procedure although procedures may vary depending upon the condition and doctor's practices. The study is performed by a neurologist although a technologist may perform portions of the test. During the procedure, the patient is asked to remove any clothing, jewelry, hairpins, eyeglasses, hearing aids, or any other metal objects that may interfere with the procedure.

The patient is asked to either sit or lie down for the test. A recording electrode is attached to the skin over the nerve with a special paste. A stimulating electrode is placed at a known distance away from the recording electrode. The nerve is stimulated by a mild and brief electrical shock through the stimulating electrode. You might experience minor discomfort for a few seconds. The patient senses rapid tingling in the area. The stimulation of the nerve and the response are displayed on an oscilloscope.

What does the test results indicate?

Generally, the nerve conduction velocity would be around 50 to 60 meters per second. But it tends to vary from person to person and from one nerve to another.

The speed of the nerve conduction study is related to the diameter of the nerve and the degree of myelin sheath (which is a type of insulation) around the nerve. While a normally functioning nerve will transmit a stronger and faster signal, a damaged nerve will be slower. The larger the wire, the better the insulation and more consistent and stronger will be the signal.

If results are abnormal, they may be due to some sort of neuropathy or damage to the nerve resulting from a traumatic injury or nerve. Sometimes, other diseases may also cause the impulses to slow down. It could be due to conduction block that is an obstacle to the impulse within the nerve or due to demyelination or damage to the myelin sheath.

Why nerve conduction study?

Nerve conduction study is done along with EMG to differentiate a nerve disorder from a muscle disorder. While nerve conduction study detects whether the nerve has any problem, EMG detects whether a muscle is functioning properly in response to the nerve's stimulus. Whenever there is any neurologic injury or disorder, nerve conduction studies often combined with needle electromyography measure are used. This helps in identifying cause for any pain or weakness in the limbs from spinal nerve compression or injury.

Nerve conduction studies are used primarily for evaluation of numbness, tingling and burning or weakness of arms and legs depending upon the part of the body the symptom is present. Physical examination by the doctor and patient's history help to direct the investigation. A number of disorders are diagnosed by nerve conduction studies - carpal tunnel syndrome, Gullian-Barre syndrome, peripheral neuropathy, spinal disc herniation, ulnar neuropathy and others.

Risks of the procedure

Although the voltage of electrical pulses used in this study is quite low, there may be risks depending upon specific medical conditions. Certain factors such as damage to the spinal cord, severe pain before the test and body temperature may affect the test. In case you are using cardiac defibrillator or pacemaker, adequate precautions need to be taken.

Ulnar Neuropathy

Ulnar nerve is a nerve that originates in the brachial plexus and travels downwards to the arm. It extends from shoulder to the wrist and branches into little finger and ring finger. It is responsible for sending sensation to the inner forearm, a portion of the palm near the little finger and half of the ring finger. Any damage caused to this nerve leads to a condition called ulnar neuropathy.

One of the most common causes of repeated neuropathy is compression. This is the only nerve in the entire body that is not well protected by bones and muscles and hence more prone to damage. The ulnar nerve can be constricted and get entrapped as it passes through the elbow and wrist. It can even be entrapped under the collarbone or at the point of origination near spinal cord. However, the ulnar nerve is commonly entrapped at the elbow and the condition is known as Cubital Tunnel Syndrome. It is also referred to as ulnar nerve compression, Ulnar nerve palsy or ulnar nerve entrapment. The other names for ulnar nerve condition are Bicycler's neuropathy and Guyon's canal syndrome.

Patients with ulnar nerve compression at any level have altered sensation in the little and ring fingers. Indeed, in most patients, sensory loss is the first symptom to be reported. As the condition progresses, they may also notice clumsiness in the hand, as the ulnar nerve is the principal motor supply to the intrinsic muscles of the hand. In well‐established cases, there may be marked wasting of the small muscles of the hand and the ulnar‐sided muscles of the forearm. Typical symptoms of this condition involve numbness and reduced sensation in the fingers. Clumsiness or weakness of the hands might be noticed. There is loss of grip and reduced coordination between fingers.

Direct injury to the nerve or pressure are primary causes for this condition. In severe cases of ulnar nerve compression, wasting of the muscles of the hand and forearm may be detected. Any injury such as fracture, dislocation or severe twisting of elbow can affect the the ulnar nerve. Pressure on the nerve caused by swelling or injury of adjacent tissue can also lead to ulnar nerve compression.

A through physical examination is conducted and history and symptoms of the patient are noted. Doctor may ask the patient to perform certain tasks with the hands to understand if the pain is arising due to ulnar nerve entrapment. Ultrasonography and/or MRI of the ulnar nerve in conjunction with nerve conduction study to assess the functioning of the ulnar nerve, can help identify the location at which it is being compressed.

Treatment of Ulnar Nerve Compression

Ulnar neuropathy is most often treatable through a conservative approach. Pain relievers and anti-inflammatory drugs are prescribed to address the pain. Steroid injections, though highly effective, are avoided as they can damage the nerve when injected in that region.

• Giving some rest to the elbow and keeping it straight relieves the pain. Doctor may prescribe a padded brace or splint to wear at night to keep the elbow straight while sleeping.
  
• Occupational therapy is also found to be highly effective in treating ulnar neuropathy as it strengthens the ligaments and tendons surrounding the elbow region and wrist.
  
• Nerve gliding exercises are also taught to release the trapped ulnar nerve through cubital tunnel at the elbow or the Guyon's canal at the wrist.
  
• When physical therapy and other forms of non-surgical treatment fail to address the pain and when the arm muscle is getting wasted, nerve entrapment surgery is the only option to treat ulnar neuropathy.

Axonotmesis

Axonotmesis is nerve injury where severe disruption of axons and surrounding endoneural sheaths takes place. Axonotmesis is characterized by axonal injury with subsequent degeneration or regeneration. The result of an Axonotmesis injury is motor, sensory and autonomic paralysis. In Axonotmesis, if the force creating nerve damage is removed in timely manner, then the axon may regenerate leading to recovery from this nerve injury. Axonotmesis is a more severe nerve injury with disruption of the neuronal axon. But in axonotmesis, the Schwann sheath is maintained. Seddon classified the nerve injury based on the extent of damage to the nerves following 'pathotofical types' on the basis of structural changes in cut nerves. The Seddon classification divides nerve injuries into three types:

Axonotmesis: Microscopic division of nerve fibers without obvious discontinuity of nerve sheath.

Neurotmesis: Complete anatomic division of the nerve fibers with obvious discontinuity of the nerve sheath.

Neuropraxia: There in injury without any anatomical discontinuity but resulting in functional disruption or nerve concussion. It is a local transient conduction blockage along the nerve.

Axonotmesis as a birth injury

As a birth injury, axonotmesis is often extremely frightening. With present day advances in the medical delivery process, there are many precautions that can be taken to lower risk for nerve injury like axonotmesis at birth. However, it must be borne in mind that not all birth related injuries are preventable. Symptoms of axonotmesis include motor and sensory loss due to blockage of conduction by demyelination. There is loss of reflex due to damage to sensory nerves. Atrophy may follow. In addition to general examination, tests may be conducted for systemic diseases such as glucose, kidney functions. A nerve conduction test is done to determine the extent of the injury. Electromyography is another diagnostic test used in axonotmesis.

In axonotmesis a complete absence of sensory modalities takes place. However, the investing sheaths of the nerve remain intact. Therefore unlike neurotmesis, recovery though delayed is likely to take place. If damage to the nerve cells has also caused destruction of the axons, there can be recovery if the supporting structures of the cells are intact. But complete recovery may not be possible. Recovery from axonotmesis can take many months. Depending upon the severity of Axonotmesis injury, full recovery can even take up an entire year. The recovery largely relies upon removal of the compressing force, timely intervention and the ability of the axon to regenerate.