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5 Articles in Volume 4, Issue #3
At-Home Teaching Materials for Chronic Pain
Diagnosis and Management of Generalized Vulvodynia
Failed Back Surgery Syndrome
Objective Documentation of Spine Pain
Trends in Pain Syndrome Diagnostic Technology

Trends in Pain Syndrome Diagnostic Technology

Current diagnostic technological devices can help identify numerous disorders of the peripheral and central nervous system in patients with chronic pain.

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.

Physical Examination

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?

Diagnostic Technology

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.

PAIN SYNDROME DIAGNOSTIC TOOLS
X-Rays
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)
Discogram
Bone Scan
Injections

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

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.

Magnetic Resonance Angiography

Magnetic resonance angiography (MRA) is an application of MRI that provides visualization of blood flow, as well as images of normal and diseased blood vessels. The use of MRA in evaluating flow in the carotid arteries, the circle of Willis, the cerebral arteries, the vertebral and basilar arteries, and the venous sinuses have been the most researched applications.

MRA provides additional imaging capabilities for intracranial aneurysms and vascular lesions. Due to its low diagnostic yield, MRA is not routinely used in the work-up of patients with non-specific, non-focal symptoms, such as headache.3,4

Magnetic resonance venography (MRV) is effective for the evaluation of diseases of larger veins. Specific indications include diagnosis of vena caval thrombus, differentiation of tumor thrombus and blood clot of the vena cava, diagnosis of superior vena caval syndrome, identification of superior vena caval invasion or encasement by lung or mediastinal tumors, diagnosis of Budd-Chiari syndrome, diagnosis of caval abnormalities, and identification of the presence and cause of obstruction and occlusion of the brachiocephalic, subclavian, and jugular veins.

CT with Myelogram

When combined with a myelogram, a CT scan provides excellent information about the nerve roots. A myelogram consists of injecting a radiographically opaque dye into the sac around the nerve roots. The CT scan shows how the bone is affecting the nerve roots, and can pick up subtle signs of pressure to the spinal cord or nerve roots, resulting in nerve impingement.

The main risk with a myelogram is the potential for a spinal headache. Spinal headaches usually resolve with rest and fluids within one-two days. If the headache continues, blood can be withdrawn from the patient’s vein and injected into the epidural space in the back. This procedure, called a blood patch, places pressure over the site that is leaking spinal fluid in order to stop the leak and resolve the headache.5,6

This test has, in most instances, been replaced by an MRI and is used primarily when there is a contraindication to a MRI, such as a pacemaker or other metal implants.

Electromyography (EMG, SFEMG, SEMG)

An electromyogram tests the functions of the nerve roots and the way that the nerves affect muscle function. It does this by looking at how well the electrical currents in the nerves and spinal pathways are being transmitted to the muscles. After several weeks of pressure on a nerve root, the muscle enervated by that nerve begins to spontaneously contract. Compression of a nerve will slow electrical conduction along that nerve. EMG’s are useful in distinguishing nerve degeneration (neuropathy) from nerve root compression (radiculopathy). By looking for abnormal electrical signals in the muscles, the EMG can show if a nerve is being irritated as it leaves the spine.

The test involves placing small needles into the muscles. This is accomplished by inserting a needle electrode into appropriate muscles, one at a time. The needle electrode allows the muscle’s electrical characteristics, at rest and during activity, to be evaluated. The muscles studied will vary depending upon the differential diagnosis. The electrical activity of the muscles is examined during both contraction and rest. Muscle twitching and contraction is felt by the patient.7

In some instances, evaluation of the paraspinal musculature may not be feasible. Examples include patients on anticoagulation medications, those with coagulation disorders or, patients having a history of surgery in paraspinal muscles, or infection in the paraspinal muscle region. It is also not feasible for a ventilator-dependent patient due to the inability to position the patient. Complete studies of the extremities require evaluation of extremity muscles innervated by three nerves or four spinal levels.

In single fiber electromyography (SFEMG), a specially designed needle electrode is used to record and identify action potentials (APs) from individual muscle fibers. These recordings are used to calculate the neuromuscular jitter and the muscle fiber density. When neuromuscular transmission is sufficiently abnormal that nerve activation produces no muscle AP, blocking is seen. Increased jitter, blocking, or both, may occur in a variety of conditions, including primary disorders of neuromuscular transmission.

Surface EMG (SEMG) employs a scanner with self-contained electrodes and/or surface electrodes that are applied to the skin, to record the electrical potential of a specific muscle or a group of muscles. SEMG has been used in the evaluation of low back pain based on the direct relationship between muscular pain and elevated myoelectrical behaviors.8-11

Nerve Conduction Velocity (NCV)

A nerve conduction study is used to evaluate the integrity of — and diagnose diseases of — the peripheral nervous system. These studies measure the conduction velocity, latency, amplitude, and shape of response following electrical stimulation of a peripheral nerve through the skin and underlying tissue. It is useful for determining whether there is a pinched nerve in the back, neck, or extremities. It is useful for confirming carpal and tarsal tunnel syndromes, peripheral neuropathy, injury from metabolic diseases such as diabetes mellitus, uremia, or chronic alcohol abuse, or other nerve entrapment syndromes. Peripheral neuropathies are common in patients with cancer, as a direct result of the malignancy, associated metabolic disturbance, or chemotherapy. Neuropathies are well recognized in viral conditions such as Hepatitis C and HIV as a result of the virus itself or as an effect of treatment.

Abnormal findings include conduction slowing, conduction blockage, lack of responses, and/or low amplitude responses. Results of NCV studies can reveal the degree of demyelination and axonal loss in the segment of the nerve examined. Demyelination results in prolongation of conduction time, while axonal loss generally leads to loss of nerve or muscle potential amplitude.

Nerve conduction velocity studies are performed by recording and studying the electrical responses from peripheral nerves or the muscle they innervate, following electrical stimulation of the nerve.

Nerves consist of fibers of variable diameter with the thicker fibers having a faster conduction velocity. Three types of fibers are generally recognized in the sensory subclass of nerve fibers:

  • A-beta fibers, the largest fibers, mediate the sensations of touch and mild pressure, as well as the sensation of position of joints and vibration
  • A-delta fibers, mediate the sensa- tion of cold and the first compo- nents of the sensation of pain
  • C fibers, the slowest and smallest, mediate the sensation of warmth and the main component of the sensation of pain.

NCV testing can provide information about:

  • Localization of focal neuropathies or compressive lesions
  • Diagnosis and prognosis of traumatic nerve injury
  • Diagnosis or confirmation of suspected generalized neuropathies (e.g. uremic, metabolic, immune, diabetic)
  • Diagnosis of neuromuscular junc- tion disorders (e.g. myasthenic syndrome, myasthenia gravis)
  • Differential diagnosis of symptom- based complaints (e.g. weakness, pain in limb, paresthesia, distur- bance in skin sensation)
  • Whether the nerve injury is an acute vs. chronic process
  • Proximal vs. distal area of the nerve injury
  • Severity of the nerve injury
  • Whether the nerve is healing

Motor and sensory NCV studies and late responses (F-waves and H-reflex studies) are often complementary. F-waves and H-reflex studies are performed to evaluate nerve conduction in portions of the nerve more proximal. Late responses provide information in the evaluation of radiculopathies, plexopathies, polyneuropathies, and proximal mononeuropathies. H-reflex studies are performed bilaterally because symmetry of responses is an important criterion for abnormality. H-reflex studies usually involve assessment of the gastrocnemius / soleus muscle complex in the calf; bilateral abnormalities are often early indications of spinal stenosis or bilateral C6-7 or S1 radiculopathies. F-wave studies enable evaluation of the upper portion of a nerve.12

Quantitative Thermal Sensory Testing

C-Fibers and A-delta fibers transmit both temperature sensing and pain transmission. Measuring heat sensitivity may provide an indirect indication of nerve health. Testing small nerve fibers for heat and cold sensitivity yields quantitative data that can be compared with normative population values. Deviation from the norm would likely indicate the existence of peripheral nerve pathway irritation or damage.

Results of NCV (nerve conduction velocity) studies can reveal the degree of demyelination and axonal loss in the segment of the nerve examined.

Measurement of thermal hypo- and hyperactivity of specific nerve pathways can help diagnose neuropathic and central thermal sensory problems and, by extension, pain transmission problems. However, this methodology does not distinguish between peripheral and central neuropathology since the measurement spans the length of a particular nerve pathway to the brain. Nevertheless, quantitative thermal sensory testing provides valuable insight to the trained clinician. Taken together with the patient’s history, physical examination, and the practitioner’s own clinical observations, an accurate diagnosis can be reached.

This methodology has been successfully utilized in diagnosing a range of neuropathic ailments including fibromyalgia, radiculopathy, polyneuropathy, overuse syndrome, complex regional pain syndrome (CRPS), and myofascial pain syndromes.13

Somatosensory Evoked Potentials (SSEP)

Somatosensory Evoked Potentials are ordered to assess the speed of electrical conduction across the spinal cord. If the spinal cord is significantly pinched, the electrical signals will travel slower than the norm.

Evoked potentials measure conduction velocities of sensory pathways in the central nervous system. In this test, a peripheral sense organ is electrically stimulated and conduction velocities are recorded for central somatosensory pathways located in the posterior columns of the spinal cord, brain stem, and thalamus, and the primary sensory cortex located in the parietal lobes.

For patients with symptomatic nerve root compression, the accurate identification of the particular nerve root(s) that are causing symptoms is an essential prerequisite to surgical intervention. The history and physical examination may be inconclusive in identifying the particular peripheral nerve root that is affected. Patients often have difficulty defining the distribution of pain or sensory symptoms, and the physical examination may be completely normal even in patients with severe pain. Imaging studies may reveal abnormalities of uncertain clinical relevance. As structural abnormalities are commonly seen in imaging studies of normal asymptomatic subjects, it is difficult to determinate whether any such abnormalities identified in pain patients are related to their symptoms. Imaging studies may show equivocal changes or anatomic abnormalities at multiple levels, making it impossible to determine which nerve root is responsible for the patient’s symptoms. In these circumstances, evoked potentials may be used to measure nerve root function and thereby more accurately identify the precise nerve roots responsible for the patient’s symptoms.

Somatosensory evoked potentials augment the sensory examination and are most useful in assessing the spinal nerve roots, spinal cord, or brain stem for evidence of delayed nerve conduction.

Dermatomal somatosensory evoked potentials (DSEPs) are elicited by stimulating the skin ‘signature’ areas of specific nerve roots. Both techniques involve production and recording of small electrophysiological responses of the central nervous system that follow sequential electrical stimulation of peripheral nerves. The small electrophysiological responses are extracted from the background noise of EEG by signal averaging techniques. Delays of signal propagation suggest lesions of the central sensory pathways. SSEP measurements have been used to predict outcome in spinal cord injury; however, signal changes on MRI may be more useful in determining the severity of injury.

SSEPs are altered by conditions that affect the somatosensory pathways, including both focal lesions (e.g. tumors, cervical spondylosis, strokes, and syringomyelia) and diffuse diseases (e.g. vitamin E deficiencies, subacute combined degeneration, hereditary systemic neurological degeneration). SSEP may be helpful in documenting abnormalities in multiple sclerosis patients with other concurrent demyelinating lesions that may not be clinically evident. SSEP abnormalities are also produced by other diseases affecting myelin.

Brainstem Auditory Evoked Responses (BAER)

Brainstem auditory evoked responses are electrical potentials produced in response to an auditory stimulus. They are recorded from disk electrodes attached to the scalp. Depending on the amount of time elapsed between the ‘click’ stimulus and the auditory evoked response, potentials are classified as early, middle, or late. The early potentials reflect electrical activity at the cochlea, eighth cranial nerve, and brain stem levels; the latter potentials reflect cortical activity. Early evoked responses may be analyzed to estimate the magnitude of hearing loss and to differential among cochlea, eighth nerve, and brainstem lesions.

The clinical utility of brainstem auditory evoked responses is due to BAER’s resistance to alteration by systemic metabolic abnormalities, medication or pronounced changes in the state of consciousness of the patient. There is a close association of BAER waveform abnormalities to underlying structural pathology. BAER is effective for differentiating conduction from sensory hearing loss, for detecting tumors and other disease states affecting central auditory pathways (e.g. acoustic neuromas, subclinical multiple sclerosis), and for noninvasively detecting hearing loss in patients who cannot cooperate with subjective auditory testing. BAER is useful in the assessment of multiple sclerosis or other demyelinating conditions, coma, or hysteria.14,15

Discogram

...evoked potentials may be used to measure nerve root function and thereby more accurately identify the precise nerve roots responsible for the patient’s symptoms.

A discogram is a test to determine the anatomical source of low back pain. This procedure is used to determine if degenerative disc disease is the cause of a patient’s pain. With age or from an injury, the wall of the spinal disc can become damaged. The wall of the disc can weaken and protrude out, or herniate. When the disc causes pain, the pain is usually felt as a deep ache in the back and sometimes in the buttocks and thigh. Pain from facet joints in the back and from the sacroiliac joints can be in the same location and feel the same.

In this procedure, the physician inserts a needle in the patient’s back into the center of the disc. Radiographic dye is then injected into the disc, imaging the internal structure. If injecting the dye recreates the patient’s normal pain (concordant), it is inferred that the specific disc is the source of the patient’s pain. If the pain is unlike their normal pain (discordant), then it can be inferred that even though the disc may appear degenerated on radiological studies, it is not the source of the patient’s pain. The patient needs to be awake and aware in order to tell the physicians what kind of pain is generated by the injection. Often, after the discogram is completed, a CT scan is performed to check the anatomy of the disc.16-19

Bone Scan

A bone scan is performed to rule out an inflammatory process, such as a tumor or infection, or an occult fracture. Bone scanning is extremely sensitive at detecting subtle stress fractures or bone tumors when they are invisible on plain x-rays since these are conditions that promote high bone turnover.

The scan is performed by intravenously injecting a radioactive marker. Several hours later, the patient is scanned. The marker will be concentrated in any region where there is high bone turnover. A bone scan can also be used to determine if a compression fracture is old or new, as an old fracture will not light up and a new fracture will.

Bone scans, however, cannot distinguish what a lesion represents, and therefore cannot differentiate between a tumor, an infection, or a fracture.

Injections

Injections can be used diagnostically to determine which structures are generating pain. For example, if an injection provides pain relief in the area that is injected, it is likely that this particular area is the source of the problem. Once the location of one or more sources of pain is discovered, other necessary tests can be obtained to determine the actual problem and fashion an appropriate treatment.

Conclusion

Numerous disorders of-and insults to-the peripheral and central nervous system can lead to chronic pain states. Due to the complexity of neural pathophysiology and often confounding presentation, diagnostic studies, in conjunction with patient history and clinical observation, can be very useful in identifying the underly- ing source and extent of injury. The availability and increasing accessibility of a wide range of technology can help the practitioner reach an accurate diagnosis and provide appropriate treatment for pain relief and rehabilitation.

Last updated on: January 5, 2012
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