Special Neurological Tests
Once the physical examination identifies the likely source of a problem, special tests are used to confirm the diagnosis. X-rays, CT scans, MRI scans, and EMG’s are examples of special tests. X-rays, CT scans, and MRI scans create pictures and show how parts of the spine look. The EMG is a functional test. It shows how things work.
One single medical test cannot offer all the necessary information needed to make a clear diagnosis of a spinal condition. Each test gives specific information that can help define the medical problem present. In most cases a physician will start with the most basic test and proceed to more sophisticated tests until a clear diagnosis has been made. Some of the common tests and imaging studies performed in evaluating spinal conditions include: X-Rays, Myelogram, CT Scan (computer tomography), bone scan, Arteriogram, discogram, MRI (magnetic resonance images), EMG (electromyograms), Sonogram (ultrasound tests), and blood tests.
The common spine X-Ray involves taking a picture of the spine by directing a beam of X-Ray through the body. The bones of the spine (which are in the middle of the body) absorb more X-Rays than the soft tissues of the lungs, abdomen, and muscle. An X-Ray picture shows a clear image of dense tissues such as the bones and not much of the soft tissues. This image can offer essential information on the structure of the bones, the relationship of one bone to the next, and the overall alignment of the spine.
It is important to realize that the spine is a complex, three-dimensional structure and that X-Rays only offer a two dimensional analysis of the spine. Therefore, to maximize the understanding of spinal shape and alignment, it is important to obtain two X-Rays of the spine, one seen from the front and the other seen from the side.
Good quality X-Rays will permit not only an analysis of the individual bones of the spine but also the overall contour of the spinal column. This is very important in such conditions such as scoliosis or kyphosis where complete analysis of spinal contour is essential.
In addition to standing and recumbent X-Rays, a physician may request a series of dynamic X-Rays to diagnose a spinal problem. These involve obtaining a set of pictures with the patient maximally bending forward and backward. This will permit an analysis of any possible instability (abnormal amounts of movement between vertebra) in the spine. Side bending X-Rays can offer significant information on the flexibility of a spinal deformity such as scoliosis. These bending films can help a surgeon in the decision-making process regarding levels of spinal fusion and overall spinal balance.
To visualize the contour and diameter of the spinal canal (located inside the spinal canal and containing the spinal cord and nerves) a myelogram may be ordered by your physician. This test involves injecting a chemical substance referred to as 'contrast' or dye into the dural sac (the fine tissue that encases the spinal cord and nerves) and obtaining either X-Rays or a Cat Scan to outline the dimensions of the canal and contour of the individual nerves.
A myelogram is particularly useful in evaluating spinal cord and nerve root compression (i.e. Spinal stenosis, spinal cord compression? Myelography may also be particularly useful in evaluating spinal problems in the setting of previous spinal surgery where instrumentation was placed. In such cases, MRI and other tests can be difficult to interpret due to the metal which has been placed in the spine.
A computerized tomogram, or CT Scan, is in essence a very sophisticated X-ray image that offers detailed 2-dimensional or 3-dimensional visualization of spinal anatomy. In simplest terms a CT Scan permits viewing slices of the spine and, through a computer program, can even reconstruct a three dimensional model of the spine that can be rotated and visualized from all directions.
A CT Scan is particularly useful in viewing the details of bone structures in the spine. Common reasons to obtain such a test include: evaluating spinal stenosis and nerve compression due to bony encroachment on the spinal canal and foramen, evaluating spinal fractures, assessing congenital abnormalities in the vertebrae, evaluating the healing of a spinal fusion. In some cases, a CT Scan is performed after a myelogram to increase the visibility of the spinal cord and nerves in the spinal canal.
This test involves the injection of a small amount of tracer material (radioactive Technetium) which is rapidly eliminated by the body through the kidneys. However, areas of bone, which are healing or have abnormal activity, will appear to hold on to the tracer in higher amounts. Therefore when a special bone scan picture is taken of the body, or a specific affected bone, increased signal (or "pick up" as it is often called) is noted in these active bone areas. A bone scan will show increased activity in conditions such as: fractures of bones, arthritis in joints, infection, healing stress injuries, tumors, and osteoporotic collapse.
This test involves injection of a special dye into blood vessels and then taking X-Ray pictures, or a film, to visualize the flow of blood through a set of vessels. Arteriogram studies are frequently performed to assess constriction or narrowing of blood vessels in atherosclerosis. In the area of spinal surgery arteriograms are rarely performed, however, they can be essential in the setting of tumors, hemangiomas, or evaluation of possible blood clots in larger vessels or the lungs after surgery.
In some cases it may be difficult to clearly identify a source of pain in the lower back. In other instances, surgery may be planned and yet it is uncertain at which level to end a fusion due to concerns over disc function at the ends of the intended fusion. In both of the above settings MRI can help make the proper decision. When an MRI is not offering sufficient information, a discogram may be ordered.
Discography involves introducing a fine needle through the skin and muscles of the back directly into the intervertebral disc with the patient awake. The location of the needle tip is verified by X-Ray imaging. Once the position is confirmed, a small quantity of special dye (contrast media) is injected into the disc. The injection increases the pressure inside the disc and if this maneuver reproduces the patient's pain, the test is considered positive. With X-Ray imaging, the outline of the nucleus pulposus in the disc can be visualized. Often a CT Scan is obtained after the discogram to clearly see the status of the disc and degree of dye leakage.
This test involves placing the patient into the area of a very strong magnet and then measuring the emitted radiation from the patient as the magnetic field is turned off. Through this technique very precise images of the various structures in the body can be obtained. MRI does not involve X-Rays or other types of projected radiation. Although the test is non-invasive it can sometimes be difficult to take for claustrophobic patients since it is necessary to be positioned inside a narrow tunnel of the machine. There are "open" MRI machines which are easier to tolerate but do not offer the same quality of images.
An MRI may be the ideal test to analyze the soft tissues around the spine, the discs, nerves, ligaments, and muscles. The shortcoming of the MRI in spinal imaging is two fold : it magnifies some bulging tissues which may create over-interpretation of disc problems. Another limitation of the MRI is the fact that it is obtained with the patient lying down in complete immobility. In degenerative disc conditions which create stenosis and instability, an MRI offers a static vision. However, very often stenosis, nerve root compression and symptoms are only present with motion (walking, turning in bed?). The degree of compression or instability may therefore not appear on the MRI and other tests may be necessary: dynamic X Rays (flexion /extension standing lateral and bending ), myelogram.
Of note, in some cases, an MRI cannot be obtained due to the magnetic field required that can affect the function of pacemakers or other devices. Patient size or claustrophobia may also be a limitation. Finally, the MRI, although excellent at analyzing most tissues, can be sub-optimal in very degenerated conditions, or areas of infection or previous spinal surgery. In some cases a special dye (gadolinium, contrast material) may be injected to enhance tissues such as scar, tumor, or inflammation and give a more accurate image. Finally, it should be noted that an MRI may not offer reliable images if instrumentation is present in the spine. A CT-Myelogram may be a more useful test in that setting.
The EMG, or electromyogram is a test, most commonly performed by neurologists or physiatrists. It involves measuring the conduction and signals across nerves and muscles. It is usually ordered to diagnose a neuropathy (nerve dysfunction) such as seen in nerve damage or neurologic disease. The test may be best suited to assess nerve disruption and recovery after trauma but can be helpful in differentiating between peripheral nerve problems (diabetes, crush injury) and more central nerve problems (nerve root compression, spinal cord injury).
SSEP's or somatosensory evoked potentials and MEP's or motor evoked potentials are tests of spinal cord function usually performed during surgery. Surgery of the spine, in the past, had the terrible reputation of being very risky regarding nerve function and potential paralysis. Newer techniques of nerve monitoring (SSEP, MEP) during surgery can provide continuous information about nerve structures to markedly reduce the chance of injury. A surgeon can thus get ongoing information about nerve conduction during an operation. If changes are noted during certain maneuvers, then modifications can be made to avoid nerve injury. Instrumentation used in the spine can also be tested during placement to ensure that nerve compression or irritation is not occurring. The SSEP and MEP monitoring techniques are of great help in increasing the safety of spine surgery; however, they are not 100% reliable and rare cases of nerve dysfunction after surgery has been noted. In some cases, when monitoring is not felt to be reliable, a surgeon may perform a wake-up test briefly during surgery to ensure nerve function.
The proper treatment of patients suffering from spinal conditions involves a team approach. Medical specialists are a crucial part of overall patient treatment. During initial evaluation a number of blood tests may be ordered to assess function of various organ systems. Some of the common tests may include: Arterial Blood Gas analysis (ABG) to evaluate oxygen concentration in the blood and lung function, Pulmonary Functions Tests (called PFT) to measure mechanical lung function, White blood cell count (WBC) and Erythrocyte Sedimentation Rate to assess the possibility of infection, chemistry panel (Chem-7 or Chem-20) to review multi-organ function and electrolyte balance