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Mathias Masem, M.D.
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Diagnostic Tests

Diagnostic Tests Glossary

 

Electrodiagnostictesting

Electromygraphy (EMG)

Nerve Conduction Study

Computed Tomography (CT SCAN)

Magnetic Resonance Imaging (MRI)

Bone Scan

 

Electrodiagnostictesting

Did you know that your body is an electrical generator? Nerves and muscles create electrical signals that deliver messages to and from your brain. Sensory nerves deliver information about your surroundings to the brain. Motor nerves deliver signals from the brain to activate your muscles.

Injuries or diseases that affect nerves and muscles can slow or halt the movement of these electrical signals. If you have pain, weakness or numbness in your back, neck or hands, measuring the speed and degree of electrical activity in your muscles and nerves can help your doctor make a proper diagnosis. This process is called electrodiagnostic testing.

    Two tests are commonly used:
  • Electromyography (EMG)
  • Nerve conduction studies (NCS)

These tests are usually administered by a neurologist (a doctor who specializes in the study of the nerves) or a physiatrist (a specialist in rehabilitation medicine).

When is electrodiagnostic testing helpful?

These tests are recommended for various conditions that can result from pressure on a nerve, particularly in the arm, elbow or wrist. These conditions are called "compressive neuropathies" and include:

  • carpal tunnel syndrome (pressure on the median nerve as it passes between the wrist bones and under the transverse ligament)
  • thoracic outlet syndrome (pressure on the brachial plexus, a cluster of nerves that passes under the collarbone at the shoulder)
  • ulnar nerve entrapment (pressure on the ulnar nerve as it passes behind the elbow)
  • cervical radiculopathy (pressure on the nerve roots as they exit the spinal column at the neck)

Electrodiagnostic testing also can be used to determine the extent of injury to a nerve after an accident and to study the effects of diseases such as diabetes.

What are the expected results from EMG and NCS?

Electromyography and Nerve Conduction Studies provide diagnostic information about the extent of the patient’s spinal problem, muscle impairment or presence of peripheral nerve compression. Both tests can differentiate an old injury from a new injury.

How accurate are the these tests?

The accuracy of electrodiagnostic tests depends on the skill of the person conducting the test and the precision of the equipment used. Generally, these tests can accurately determine injuries to the nerves or nerve roots as well as diseases of the nerves and muscles. In some conditions, however, it may take several weeks for changes to become apparent. Additionally, the tests cannot determine the existence or extent of pain. A person may still feel pain or exhibit symptoms even though electrodiagnostic tests show that the nerves are functioning normally. In these cases, your hand surgeon will recommend a course of treatment for you.

 

Electromygraphy (EMG)

What is an EMG?

Electromyography (EMG) is a diagnostic study to determine if there is any impaired muscle activity. It is used to learn more about the functioning of nerves in the arms and legs. When a normal muscle is at rest, it is electrically silent.

How is it done?

During the EMG, small, thin needles are placed in the muscle to record the electrical activity. When the needles are inserted, you may feel some mild pain or discomfort. The doctor will ask you to relax the muscle and to tense it slightly. The doctor will listen and watch a TV-like screen that broadcasts the electrical signals. You will also be able to hear the signal sounds as you move the muscle. The results are compared with normative data and allow the physician to determine if there is any muscle impairment.

For upper extremity conditions, the patient sits on the side of an exam table supported at the back by pillows. Jewelry must be removed from the hands and wrists. The arms and hands are placed on a pillow on the patient’s lap.

For lower extremity or spine conditions, the patient is positioned prone on the exam table and electrodes are placed on both leg calves.

How long does it take?

The procedure take up 60 minutes each. You should be able to drive yourself home after the completion of the tests.

 

Nerve Conduction Study

What is a Nerve Conduction Study (NCS)?

NCS are often done along with the EMG to determine if a nerve is functioning normally. A nerve conduction study (NCS) is used to determine if the conduction rate of the nerves has been compromised anywhere along the nerve’s pathway. The electrical conductivity is compared to a normative baseline to determine if there is compression on a specific nerve in a specific area.

How is it done?

The physician conducting the test will tape wires (electrodes) to the skin in various places along the nerve pathway. Then the nerve is stimulated with an electric current. As the current travels down the nerve pathway, the electrodes placed along the way capture the signal and time how fast the signal is traveling. In healthy nerves, electrical signals can travel at up to 120 miles per hour. If the nerve is damaged, however, the signal will be slower and weaker. By stimulating the nerve at various places, the physician can determine the specific site of the injury. Nerve conduction studies also may be used during treatment to test the progress being made.

Although you may initially be startled by the suddenness of the stimulation, it is not painful and most people are comfortable during the testing procedure. The shock is similar to one received when you touch a doorknob after walking across carpeting.

How long does it take?

The procedure take up 60 minutes each. You should be able to drive yourself home after the completion of the tests.

 

Computed Tomography (CT SCAN)

What is a Computed Tomography (CT Scan)?

CT (computed tomography), sometimes called CAT scan, uses special x-ray equipment to obtain image data from different angles around the body and then uses computer processing of the information to show a cross-section of body tissues and organs.

CT imaging is particularly useful because it can show several types of tissue—lung, bone, soft tissue and blood vessels—with great clarity. Using specialized equipment and expertise to create and interpret CT scans of the body, radiologists can more easily diagnose problems such as cancers, cardiovascular disease, infectious disease, trauma and musculoskeletal disorders. This information allows your physician to determine an appropriate treatment plan.

A CT scan may be ordered if your doctor suspects a tumor, a fracture that doesn't appear on X-rays or if you've had severe trauma to the chest, abdomen, pelvis or spinal cord. The process is painless. You lie motionless on a table as it slides into the center of the cylinder-like CT scanner. An X-ray tube slowly rotates around you, taking many pictures from all directions. A computer combines the images to produce a clear, two-dimensional view on a television screen.

You may need to drink or be injected with barium sulfate or a dye so that certain parts of your body can be seen more clearly. The drink has a chalky taste and may make you feel nauseous; a dye injection may be moderately painful. Tell your doctor if you are pregnant before undergoing a CT scan.

 

Magnetic Resonance Imaging (MRI)

What is Magnetic Resonance Imaging (MRI)?

Magnetic resonance imaging (MRI) uses radiofrequency waves and a strong magnetic field rather than x-rays to provide remarkably clear and detailed pictures of internal organs and tissues. An MRI uses a sophisticated computer to take high-resolution pictures of your bones and soft tissues, resulting in a cross-sectional image of your body.

What are some common uses of the MRI procedure?

Because MRI can give such clear pictures of soft-tissue structures near and around bones, it is the most sensitive exam for spinal and joint problems. MRI is widely used to diagnose sports-related injuries, especially those affecting the knee, shoulder, hip, elbow and wrist. The images allow the physician to see even very small tears and injuries to ligaments and muscles.

How is a MRI done?

As with a CT scan, you lie on a table that slides into the tube-shaped MRI scanner. The MRI creates a magnetic field around you, then pulses radio waves to the area of your body to be pictured. The radio waves cause your tissues to resonate. A computer records the rate at which your body's various parts (tendons, ligaments, nerves) give off these vibrations, and translates the data into a detailed, two-dimensional picture. You won't feel any pain while undergoing an MRI, but the machine may be noisy. An MRI takes 30 to 90 minutes, and is not available at all hospitals. Tell your doctor if you have implants, metal clips or other metal objects in your body before you undergo an MRI scan.

 

Bone Scan

What is a Bone Scan?

One type of bone scan is used to identify areas where there is unusually active bone formation. It is frequently used to pinpoint stress fracture sites or the presence of arthritis, infection, or cancer. About three hours before the scan, you will be given a dose of a mildly radioactive substance called "technetium" through an intravenous line (IV). This substance occurs naturally in your body and is used in the bone formation process. The bone scan itself is performed about three hours later, which gives the bone time to absorb the technetium. As you lie on a table, a special nuclear camera takes a picture of your entire body. This process takes 30 to 90 minutes. Areas of abnormal bone formation activity will appear brighter than the rest of the skeleton.

No fasting or other preparation is required. The amount of radioactivity absorbed during a technetium bone scan is minimal, and there are usually no side effects. You may feel some discomfort as the IV line is placed. Some people may feel nauseous. Tell your physician if you are or may be pregnant or are a nursing mother before you schedule this test.