Trends in Pain Syndrome Diagnostic Technology
The pathophysiology of nerve injury in chronic pain can be highly complex and can lead to unpredictable response to treatment. Getting an accurate diagnosis is critical, because different diagnoses most likely require very different treatment approaches. The sooner an accurate diagnosis is made, the sooner the patient can find an appropriate treatment for pain relief and rehabilitation. An accurate clinical diagnosis is typically based on correlating the findings of the diagnostic tests with the patient’s specific symptoms and the physician’s findings from a complete physical examination. Diagnostic studies are useful for identifying the source and extent of the injury as well as to assist in the diagnosis and development of an appropriate treatment plan. Diagnostic studies also play a useful role in outcome measurement to confirm treatment efficacy.
The medical history, the pain history, and the findings of the physical examination have historically been used to evaluate the nociceptive system.1,2 Depending on the findings, patients may be given:
- Prescription for medications
- Self-care instructions
- Physical therapy referral
- Referral for diagnostic tests
A comprehensive physical examination includes the evaluation of pain characteristics, such as:
- When did the pain first begin?
- How long has the pain been present?
- Does the pain stay in one spot or travel?
- Is the pain associated with numbness, tingling, or weakness?
- What time of day is the pain the worst?
- What are the exacerbating and relieving factors?
- What are the associated signs and symptoms?
- How does the pain interfere with daily activities?
- What is the impact of the pain on the patient’s psychological state?
- What has been the response, or lack of, to previous analgesic therapies?
- Is the pain neuropathic or nociceptive?
Advances in diagnostic technology (see Table 1) has given the practitioner an unprecedented arsenal in evaluating peripheral and central nervous system pathology. At the same time, more traditional imaging techniques continue to provide value in helping to exclude physiological pathologies that may be contributing factors. For example, imaging studies may be used to confirm an anatomical lesion as a cause of either pain, progressive weakness, or neurological loss of function.
|Computerized Tomography (CT scan)|
|Magnetic Resonance Imaging (MRI)|
|Magnetic Resonance Neurography|
|Magnetic Resonance Angiography|
|Magnetic Resonance Venography|
|CT with Myelogram|
|Electromyography (EMG, SFEMG, SEMG)|
|Nerve Conduction Velocity (NCV)|
|Quantitative Thermal Sensory Testing|
|Somatosensory Evoked Potentials (SSEP)|
|Brainstem Auditory Evoked Responses (BAER)|
Table 1. A selection of tools useful for pain syndrome diagnostic studies.
The following sections discuss the strengths and limitations of the various diagnostic modalities in assessing the pathophysiology of the peripheral and central nervous system.
X-rays provide detail of bony structures and are typically used to evaluate for instability, misalignment, abnormal motion, tumors, and fractures. X-rays provide for excellent bony detail because bone consists mainly of calcium. However, an x-ray cannot be used to diagnose disc herniation or other causes of nerve pinching.
Computerized Tomography (CT Scan)
A CT scan takes cross sectional images of the body and provides excellent bony detail as well as providing the capability of imaging soft tissue structures, such as discs, spinal cord, and nerve roots, to rule out disc herniation, tumors, etc. A computer is used to reformat the image into cross sectional images, or ‘slices’, of body tissues, bones and organs at multiple different intervals. If needed, three-dimensional images of the internal organs and structures of the body can also be generated.
CT imaging is particularly useful because it can show soft tissues in addition to bones, and is the principal imaging technique for demonstrating lungs and abdominal organs. CT imaging is also used to generate high resolution pictures of bones when subtle tumors or fractures are suspected.
Magnetic Resonance Imaging (MRI)
The MRI provides a clear diagnostic picture without using radiation. It uses radio waves in conjunction with a very powerful magnet and computer processing to generate realistic pictures of various parts of the body. The MRI image provides detailed images of soft tissues, particularly the brain, spinal cord, muscles, ligaments and cartilage and is used for evaluating these structures. The MRI provides excellent bony detail and can look at the shape and hydration of intravertebral discs, and is capable of imaging soft tissue structures, to rule out bulging, herniated, or ruptured discs, degenerative disease, tumors, fractures, and soft tissue lesions.
Nerves generally cannot be seen well on standard MRI scans. From the point at which a spinal nerve is about one centimeter from the spinal canal, and on out through the rest of the body, standard imaging cannot be used to confirm or disprove an injury.
Magnetic Resonance Neurography
MR Neurography is a means of optimizing an MRI scan for sensitivity to special biophysical properties of nerve. In MRI scanning, the scanner is able to detect subtle differences in the behavior of protons which are most abundant in water. Water in different tissues may appear differently in the image due to the effects of material dissolved in the water which affect the tumbling rate of the water molecules. It may also be affected by magnetic properties of materials dissolved in or near the water. The way in which water molecules move or diffuse in tissues can also affect their appearance in the image. The second most abundant source of protons are those participating in fat or lipid molecules. It is possible to use radiofrequency pulses and magnetic field shifts to accentuate the appearance of one type of proton over the appearance of another.
MR Neurography is promoted for the diagnostic evaluation of conditions thought to be due to nerve compression or impingement, trauma involving peripheral nerves, and repetitive strain injuries.