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.

Friedreich's Ataxia

Friedreich's ataxia is an autosomal recessive inherited disease which may cause progressive damage to the nervous system. This form of ataxia results from degeneration of nervous tissues in the spinal cord (the nerves get thinner). The sensory neurons are damaged thus affecting the muscle movement of the legs and arms. The condition does not affect the cognitive functions (reasoning and thinking ability).

The condition may set in childhood and may worsen with age thus completely crippling the movement of a person. The condition can incapacitate a person and confine him/her to a wheelchair. Friedreich's ataxia is the most common form of hereditary ataxia. This condition may reduce the life span of the person.

Friedreich's Ataxia Cause

Individuals develop this condition only if they have inherited two copies of the defective FXN gene, one from the father and one from the mother. If the person has only copy of the gene, he/she is called the carrier and may not develop the disease but may pass on the gene to his/her kids in the future. About 1 in 90 Americans of European ancestry is a potential carrier.

Friedreich's ataxia symptoms

Children with FA or Friedreich's ataxia tend to trip often and graze furniture and doorways. Muscle cramps and spasms are often experienced. Nystagmus occurs at an advanced stage along with loss of visual acuity.

• Weakness of muscles in the arms and legs
  
• Hearing impairment
  
• Loss of coordination
  
• Vision impairment
  
• Slurred speech
  
• Scoliosis (curvature of the spine)
  
• Deformity in the feet
  
• Shortness of breath
  
• Palpitations
  
• Diabetes in some people

Friedreich's ataxia diagnosis

Diagnosis includes physical examination by the physician and the following tests:

• ECG to understand the heart beat pattern.
  
• EMG to understand the electrical activity in the muscles.
  
• Echocardiogram for better understanding of the heart's performance.
  
• Blood tests to check the elevated glucose level in blood and to check vitamin E levels.
  
• MRI and CT scans to understand the brain and spine functioning.
  
• Nerve conduction studies to assess and measure the speed of nerve impulses

Friedreich's ataxia treatment

Though there is no proven treatment for Friedreich's ataxia, the associated symptoms can be treated. Physical therapy for orthopedic problems, cure for diabetes can be offered.

Charcot MarieTooth Disease

Charcot MarieTooth disease or CMT, also called as hereditary motor and sensory neuropathy, is a group of inherited disorders that cause damage to peripheral nerves. The disease is named after three physicians Jean Charcot, Pierre Marie, and Howard Henry Tooth, who researched about the condition. The condition is progressive, meaning, the muscles of the arms and legs of CMT patients become weak over a period of time. CMT is a genetic disorder and is caused by many different gene mutations. Since 1991, 90 different genes causing CMT have been identified and the list continues to grow.

Signs and symptoms

CMT patients usually begin to notice symptoms in adolescence or early adulthood. Charcot MarieTooth disease affects both motor and sensory nerves and hence results into both motor symptoms (weakness and muscle wasting) and sensory symptoms such as numbness and tingling in extremities. Very rare symptoms of CMT include breathing problems, hearing loss, speech and swallowing problems.

• Muscle weakness leading to Foot Drop
  
  
• High-stepped gait
  
  
• Frequent tripping and falling
  
  
• Stork-like legs due to muscle atrophy
  
  
• Dropping things
  
  
• Clumsiness
  
  
• Bone deformities
  
  
• Hammertoes and High arches
  
  
• Decreased deep tendon reflexes
  
  
• Sensory loss

Diagnosis and treatment

Examining patient's medical history and family history forms the basis for diagnosing Charcot MarieTooth disease. After noting down the symptoms, doctor may further order nerve conduction studies, electromyography (EMG), nerve biopsy, genetic testing and bone X-rays. Nerve biopsy might be done to check for appearance of CMT. Genetic testing is used to check for mutations that cause CMT.

CMT is not a fatal disease and people with most forms of CMT have normal life expectancy. However there is no cure for Charcot MarieTooth disease. It only needs to be managed depending upon the symptoms of the patient. Physiotherapy plays a major role in improving the condition of CMT patients. Physical therapy involving stretches and light exercises helps in building muscle strength and preventing atrophy. Depending on the symptoms, orthopaedic devices such as splints and braces may be used to maintain the mobility of the limbs. If the patients have severe foot deformity, it can be rectified through surgery to help them walk with ease. It can be supported with use of orthotics - specialized shoes.