Recent Studies

Updated anthology is available on the website

PPM Logo

A-Delta Pain Fiber Nerve Conduction Study Benefits Patients With Spinal Pain

Of 151 pain fiber nerve conduction studies administered to patients with cervical and lumbar spinal pain, 56% changed treatment plans for the patient and 35% confirmed the planned treatment. Additionally, in 8% of patients, the studies changed the side of the patient receiving treatment.

By Peter M. Carney, MD, FAANS

Because spinal pain has many causes, any test that can accurately diagnose the source of pain serves as an invaluable tool for making sure the patient receives the correct treatment. A 2002 study by Cork et al studied the nerve conduction of pain fibers with a device that had 94.6% sensitivity in detecting lumbar nerve-root function pathology as confirmed by epidurograms.1 The basis for this type of testing is the pain fiber nerve conduction study (pf-NCS). The pf-NCS uses electrical voltage applied at predetermined points that correspond to areas innervated by a specific nerve root 2 to determine whether that nerve root has a normal response to the current. A hyperresponse indicates increased sensitivity to the current, while a hyporesponse indicates impaired sensitivity of that nerve root.

Despite the sensitivity of the pf-NCS, no prospective clinical studies have been able to demonstrate that the pf-NCS improves the management and clinical outcomes of patients with spinal pain any better than other methods. Indeed, the Center for Medicare and Medicaid Services in 2004 concluded that prototype devices (like that used by Cork), which relied on the patient's psychophysiological assessment (perception of a sensation), were unacceptable for Medicare coverage because, "there continues to be insufficient scientific and clinical evidence to consider the pf-NCS test and device used in performing this test as reasonable and necessary."3

More recently, however, the use of a potentiometer, in conjunction with pf-NCS, precisely recorded an objective increase of 20 millivolts or more a second or two before the patient felt a sensation generated by the pf-NCS.4 Thus, theoretically, the pf-NCS gives more than just a "psychophysiologic assessment" as to whether a given patient perceives pain.

This study was undertaken to determine the effectiveness of the pf-NCS in improving outcomes of patients suffering from cervical and lumbar pain. The pf-NCS (performed with a Neural-Scan, PainDX, Inc., Laguna Beach, California) employs a voltage-regulated stimulus in conjunction with a potentiometer, an objective measurement of the amplitude of the action potential.

Evaluating the sensitivity of the test in determining which nerve generates a given patient's pain, as well as the specificity of that test in reducing the patient's pain while improving the patient's function, will demonstrate whether the use of the pf-NCS is "reasonable and necessary."

From August 1, 2008, through July 31, 2009, 151 individual pf-NCS electrodiagnostic examinations were performed on 124 patients, who were then followed for at least 1 month after receiving treatment. The patients' ages, sexes, clinical diagnoses as determined by history, physical findings, x-rays/magnetic resonance imaging/computed tomography scans, and results of the pf-NCS were recorded. The pf-NCS results demonstrated that a given nerve root had one of six responses: a normal, mild, moderate, marked, severe, or very severe reaction (see box). All patients had their visual analog scale (VAS) and Oswestry Disability Index (ODI) measured and recorded before and after they received treatment. Patient treatment was dependent upon what the pf-NCS showed to be causing the patient's pain.

If the results were normal, the patient underwent conservative treatments including physical therapy, medication, and counseling where indicated. If the results showed mild, moderate, or marked nerve root abnormalities, then diagnostic medial branch facet joint blocks (MBB) were performed at the appropriate level according to International Spine Intervention Society Guidelines,5,6 and medial branch facet rhizotomies were performed when indicated.7,8 If the results showed severe or very severe nerve root abnormalities, then transforaminal lumbar epidural steroid injections (TF/LESI), LESI, or cervical epidural steroid injections (CESI) were performed at the appropriate level. Some patients received other interventional techniques such as sacroiliac (S/I) joint injections, piriformis injections, percutaneous disc decompression (Disc Dekompressors, Stryker, Kalamazoo, Michigan), or vertebroplasties.

pf-NCS results

The test results were then divided into three categories (Table 1). The treatment selected for a given patient was considered to have "helped" if the patient's VAS was reduced by at least 2 points or 25% and/or the ODI was less than 40 and improved by at least 25%.9 Overall average changes in the VAS and ODI were evaluated using several different parameters. In addition, the patients were divided into those who had pf-NCS of either the lumbar or cervical spinal regions and evaluated according to the treatment given to them and their response to treatment.

Data from 151 pf-NCS were analyzed. The average patient age was 56.9 years, with a range of 14 to 94 years; 59 men and 92 women were tested. Of the patients tested, the average decrease in VAS score was 49% and an average functional improvement in the ODI was 44%. When analyzed by category, results of the pf-NCS had one of three influences on the treatment patients received: change in the treatment given (56%, n=84); confirmation of what clinical findings recommended as appropriate treatment (35%, n=53); no influence on treatment (9%, n=14).

Of those 84 patients where the pf-NCS helped change treatment, 72 tests (86%) helped patients decrease their VAS scores by 75%, on average, and demonstrated approximately 42% improvement in functioning. Of special note are the 12 patients where the pf-NCS changed the side that received treatment (8%). None of these 12 patients would have had the correct side of their pain generator treated without the use of the pf-NCS. On average, these 12 patients demonstrated an 88% decrease in their VAS and a 54% improvement in function.

As noted, the pf-NCS also confirmed what the patient history, physical findings, and diagnostic tests such as plain x-ray films, CT scans, and MRIs suggested should be the appropriate treatment. Of these 53 patients, improvement was seen in 40 patients (75%), while 13 patients (25%) were not helped. The average patient in this group decreased their VAS by 55% and improved their ODI by 55%.

Fourteen of the pf-NCS did not influence the treatment a given patient received; 6 patients (43%) were helped anyway and 8 patients (57%) were not helped. On average, those treated in this group had a 42% decrease in VAS and a 27% improvement in ODI.

Test Categories

Treatment Procedures
The pf-NCS resulted in 151 procedures or therapies being evaluated; 40% of all the pf-NCS (60) suggested that diagnostic MBBs should be done. These 60 MBBs resulted in 44 medial branch rhizotomies (MBR) being performed while results from 16 of the MBBs did not recommend that an MBR be performed (Table 2). Of the MBBs administered, 12 gave such long-term relief with just the use of local anesthetic that no MBR was needed; 4 of the MBBs failed to indicate that the patient would benefit from an MBR. Patients were helped by 50 (83%) of the diagnostic block procedures while 10 procedures (17%) did not help. The average patient in this group had a 63% decrease in VAS and a 32% improvement in ODI. TF/LESI was suggested by 34% of all pf-NCSs (51), which helped 49 patients (78%), but did not help 11 patients (22%). The average patient in this group had a 46% decrease in VAS and a 34% improvement in ODI.

Data from 19 pf-NCS (13%) suggested that patients should receive medical therapy. These conservative therapies helped 10 patients (53%) who received them but did not help 9 patients (47%). The average patient in this group had a 38% decrease in VAS and a 26% improvement in ODI.


Only 9% of all pf-NCS (14) resulted in other treatments being given. These procedures included S/I joint injections, piriformis injections, percutaneous Disc Dekompressors, or vertebroplasties. Of these procedures, nine (64%) helped, but five (36%) did not. The average patient in this group had a 65% decrease in VAS and a 34% improvement in ODI. Interlaminar epidural steroid injections were done in 4% of all pf-NCS (6), three in the cervical spine and three in the lumbar spine. Three of these procedures (50%) helped and three (50%) did not. The average patient in this group had a 65% decrease in VAS and a 14% improvement in ODI.

Anatomic Location
Of the 151 pf-NCS performed, 40 were done for problems in the cervical spine (36%) and 111 for problems in the lumbar spine (64%) (Table 3). In 16 patients who received lumbar pf-NCS, various forms of medical therapy were recommended including oral steroids and physical therapy, which helped 10 patients (63%). Other forms of interventional treatments including S/I joint injections, piriformis injections, percutaneous Disc Dekompressor procedures, and vertebroplasties, were administered for 11 patients; seven of these procedures helped (64%).

Cervical vs. Lumbar

The use of pf-NCS in this series showed that more than half (56%) of the tests performed changed the treatment planned for the patient, approximately one third (35%) confirmed the planned treatment, and less than one tenth (9%) did not influence the treatment. The pf-NCS changed the planned therapy due to several factors. The test demonstrated which level generated the patient's pain when the MRI showed "multilevel degenerative disc and facet changes," and also changed the diagnosis of the pain generator from the disc to the facet or vice versa.

Additionally, the pf-NCS determined the best therapy for the patient, and confirmed in 12 patients that the generator of a patient's pain was located on the opposite side of the patient's body. This last finding was very significant.

The data in this study offer clear and convincing "scientific and clinical evidence to consider the pf-NCS electrodiagnostic examinations" as both a "reasonable and necessary" aid in helping all who wish to practice scientific and effective pain medicine.

If other studies confirm these findings, then an important diagnostic tool will be available to greatly improve the surgical, interventional, and medical treatment of spinal pain.

Paradoxical Relationship: A-Delta Function and VAS

Authors: Randall Cork, MD, PhD
Michael Bezel, MD

The A-delta pain fiber nerve conduction study (A-delta pf-NCS) measures the sensitivity of fast pain fibers known to down-regulate soon after injury. This study compares changes in the sensitivity of the A-delta fibers in pathological nerve-roots with changes in the patient's subjective visual analog score (VAS). A significantly close relationship was found between the change in voltage required to cause an action potential (nerve impulse) in the A-delta fibers of the pathological nerve-root and changes in the subjective VAS rating. The findings support the utility of the A-delta pf-NCS for detecting the level and side of painful radiculopathy and measuring changes in pain.

An objective marker associated with the patient's subjective pain perception has been an elusive challenge. A multitude of scales have been proposed in the attempt to quantify the severity of pain experienced by the patient and to quantify the response to treatment. The visual analog scale (VAS) has been widely used as a gauge of pain severity in acute and chronic pain. 1,1,1,1 The A-delta small pain fiber nerve conduction study (pf-NCS) is used to locate pain generators. For several decades physiology texts have described that during the first epicritic phase of sensory nerve injury the A-delta fibers up-regulate causing a withdrawal reflex. This is shortly followed by the protopathic phase in which Guyton & Hall Textbook of Medical Physiology explains that the fibers capable of almost exact localizing, the A-delta fibers, down-regulate and the poor localizing C- Type fibers begin to up-regulate. Concerning this protopathic phase Guyton states; "It explains why patients often have serious difficulty in localizing the source of some types of chronic pain. "1 Cork, et al showed that the nerve-root adhesion causing radicular pain was associated with hypo-sensitivity of A-delta fibers in the associated peripheral nerve. 1 Other studies have used hypo-sensitivity of the A-delta fibers as detected by the pf-NCS as an objective marker for pain. 1,1,1

The purpose of this study was to survey the clinical association between the patient's VAS pain rating and sensitivity of the A-delta fibers as measured by the pf-NCS.

A study group was formed from members of the American Association of Sensory Electrodiagnostic Medicine certified in A-delta pf-NCS electrodiagnostic examination (EDX). After IRB approval of the study by AASEM the study group members were asked to submit A- delta pf-NCS studies using the Neural-ScanTM (PainDX, Inc. of Laguna Beach, Ca. ) for those patients who reported a change in VAS after treatment for pain. After one month, 83 pairs of VAS ratings and the associated graphs of the A-delta pf-NCS made on the same day were received. Data analyzed included the pre-treatment and post- treatment VAS pain scores, difference in the voltage required to cause an action potential of the A-delta fibers in the pathological nerve-root identified by the pre A-delta pf-NCS of the peripheral nerve associated with the nerve-root identified by the pre A-delta pf-NCS of the peripheral nerve associated with the nerve-root, sex and spinal region (cervical or lumbar). Data were analyzed using repeated-measures analysis of variance. Results were considered significant if p<0. 05.

Change in VAS and voltage inducing an action potential are shown in Figure 1. Both VAS and voltage decreased with treatment (p<0. 001).

Pain Score

Figure 1. Change in VAS and threshold voltage with pain treatment.

Both sex and spinal level were significantly associated with threshold level (p<0. 05), but neither was significantly associated with VAS. A- Delta threshold voltage decreased from 28. 4±1. 4 v (SEM) (n=43) to 18. 7±1. 4 v for males (p<0. 001) and from 24. 6±1. 1 (n=40) to 16. 5±1. 0 v for females (p<0. 001). Figure 2 illustrates the different voltage thresholds for each sex and how threshold level changed with treatment for males and females.

Volts / Treatment

Figure 2. Decrease in threshold voltage for males and females with treatment. Males showed higher threshold levels than females (p<0.05), and threshold levels for both males and females decreased with treatment (p<0.001).

Threshold voltage for cervical dermatomes was significantly lower than threshold voltage for lumbar dermatomes (p<0.05). Threshold voltage decreased from 23.0±1.4 v (n = 36) to 14.6 ± 1.0 v (p<0.001) for cervical dermatomes and from 29.3±1. 1 v (n = 47) to 20 ± 1.0 v (p<0.001) for lumbar dermatomes. Figure 3 illustrates how lumbar voltage thresholds were significantly higher than cervical voltage thresholds (p<0.05) and how both lumbar and cervical thresholds decreased with treatment (p<0.001).

Volts / Treatment

Figure 3. Decrease in threshold voltage for cervical and lumbar dermatomes with treatment. Lumbar dermatomes showed higher threshold levels than cervical dermatomes (p<0.05), and threshold levels for both lumbar and cervical dermatomes decreased with treatment (p<0.001).

In contrast to threshold voltage, VAS response was not different for males compared to females or for cervical dermatomes compared to lumbar dermatomes. Figure 4 shows the response to treatment for both males and females. Although there is a significant treatment effect (p<0.001), there is no difference in VAS response based on sex.


Figure 4. Change in VAS for both males and females in response to treatment. Although there is a significant treatment effect (p<0.001), there is no difference in treatment response based on sex.

Figure 5 shows a similar response to treatment for both the cervical and lumbar region. Again, although there is a significant treatment effect (p<0.001), there is no difference between cervical and lumbar VAS responses.

Figure 5. Change in VAS for both cervical and lumbar regions in response to treatment. Although there is a significant treatment effect (p<0.001), there is no difference in treatment response based on spinal region or level.

These data represent the results of a survey of members of the American Association of Sensory Electrodiagnostic Medicine. Thus, the responses to treatment reported may be biased by members submitting "typical" responses that make the treatment look good. Nonetheless, the focus of the survey was not on the effectiveness of treatment, but on how the response to treatment, as measured by VAS, was associated with the response to treatment as measured by the threshold voltage of the A-delta fibers. On the basis of these results, A- delta fiber threshold voltage is a good independent marker of pain decrease with successful treatment, independent of the pain report given by the patient. This is a significant finding, as patient perceptions are very subjective and affected by many extraneous variables, including malingering.


Why females should have lower A-delta threshold voltages is an interesting question that certainly deserves more research. Similarly, why the cervical region would have lower A-delta fiber voltage thresholds than lumbar region is another potential area of investigation. However, the study data shows clearly that A-delta function as measured by voltage threshold is dependent on both sex and spinal region. With adjustments for sex and spinal region, A-delta hypo- sensitivy appears to be an objective marker for measuring the success of therapeutic interventions.

A-delta sensitivity/function as measured by voltage threshold using the pf-NCS is related to the patient's pain perception. As A-delta sensitivity improves from hyposensitivity to normal sensitivity, pain decreases; as A-delta sensitivity/function deteriorates, pain increases. Females have lower A-delta fiber voltage thresholds than males, and the cervical region exhibits lower A-delta fiber voltage thresholds than the lumbar region, but the A-delta voltage thresholds drop independently of sex and spinal level with treatment. In contrast, the VAS responses are not different based on either sex or spinal level, but VAS drops significantly in concert with the drop in A-delta fiber sensitivity/function. In general, A-delta sensitivity/function measured by A-delta small pain fiber nerve conduction study (pf-NCS) is an excellent objective measure of pain change following treatment, and a practical and painless electrodiagnostic procedure for detecting the side and level of painful radiculopathic pain generators.

1Bijur PE, Silver W, Gallagher EJ: Reliability of the visual analog scale for measurement of acute pain. Academy of Emergency Medicine. 2001 Dec;8(12):1153-7.

1Bijur PE, Latimer CT, Gallagher EJ: Validation of a verbally administered numerical rating scale of acute pain for use in the emergency department. Academy of Emergency Medicine. 2003 Apr; 10(4):390-2.

1 Holdgate A, Asha S, Craig J, Thompson J: Comparison of a verbal numeric rating scale with the visual analogue scale for the measurement of acute pain. Emergency Medicine (Fremantle). 2003 Oct-Dec;15(5-6):441-6.

1Salaffi F, Stancati A, Silvestri CA, Ciapetti A, Grassi W: Minimal clinically important changes in chronic musculoskeletal pain intensity measured on a numerical rating scale. European Journal of Pain. 2004 Aug;8(4):283-91.

1Guyton & Hall Textbook of Medical Physiology 11th Ed. , 2006: 601.

1Cork RC, Saleemi S, Hernandez L, Schult T, Brandt S: Predicting nerve root pathology with voltage-actuated sensory nerve conduction threshold. The Internet Journal of Anesthesiology, (6:1), 2002.

1Badruddoja M, Bush IM, Irshad M, Bush AP, Aguillar F: Chronic prostatitis causing pelvic pain due to sacral entrapment. Presented at the American College of Surgeons, October 10, 2008

1Hernandez L, Chaubey R, Cork RC, Brandt S, Alexander L: Treatment of Piriformis Syndrome with Botox. The Internet Journal of Anesthesiology, www. ispub. com, 6(2), 2003

1 Raza H, Zavisca F, Hernandez L, Brandt S, Chaubey R, Isaac I, Cork R, Alexander J, Alexander L: Treatment of Piriformis Syndrome with Botulinum Toxin-A, Using V-sNCT to Aid Diagnosis. The Internet Journal of Anesthesiology, www. ispub. com, 7(1), 2003.

Neural Scan
Neural Scan

Neural Scan
Neural Scan
Neural Scan
Neural Scan
Neural Scan
Neural Scan

A-Delta Fiber

Transforamenal study - Presented at the 5th Annual AASM Conference - 2006

Pain Fiber Nerve Conduction Sensory Testing: Randall C. Cork, MD, PhD; Shweta Khedlekar, BS; Sanjay Madnani, MD Ahmad Elsharydah, MD; Paul Mayes, MD Department of Anesthesiology Louisiana State University Health Sciences Center, Shreveport, LA USA 7113
Introduction: Nerve conduction sensory (PF-NCS) test helps to diagnose severity, location & distribution of radiculopathy or neuropathy.

Non-invasive method.

Measures sensory threshold using neuroselective frequency to test Type A-delta fibers.

Abnormally high PF-NCS measures indicate significant nerve conduction loss.

Abnormally low PF-NCS indicate hyperesthetic state that corresponds with inflamed, irritated or regenerating nerves. Methods: PF-NCS tests are performed on patients with lumbar pain, before & after interventional pain procedures.
Time period between pre & post procedure PF-NCS test = 2 weeks.

Patients complete forms to communicate their intensity of pain, functional impairment, depression & anxiety.

Patient charts undergoing procedures at the LSUHSC Pain Clinic between Sept 2005 & Feb 2006 reviewed.
Data analyzed using Student's Paired t-test & Chi-square tests (significance defined as p<0.05).
Pain charts of 53 patients reviewed.

Significantly decreased PF-NCS scores after lumbar interventional procedures (p<0.001).

Lumbar Pain Patients - Paired T-test indicated significant changes in McGill Pain Questionnaire & Oswestry Disability Questionnaire with p=0.012 and p<0.001 respectively.

Transforaminal ESI & Interlaminar ESI resulted in decreased PF-NCS (p<0. 05).

No significant change in number of abnormal dermatomes.

Pain intensity (McGill) & functional (Oswestry) pain scores significantly reduced following Transforaminal ESI, but not Interlaminar ESI.

Depression (Beck) & anxiety (PRAS) significantly reduced following Interlaminar ESI, but not Transforaminal ESI.

Transforminal ESI

Transforminal ESI

Transforminal ESI

Conclusion: PF-NCS - direct sensory test.
Assesses peripheral sensory nervous system by measuring voltage intensity which initiates membrane potential changes to propagate nerve impulses.
Physician can identify a target & assess results of interventional pain procedures.
Cork R C, Saleemi S, Hernandez L, Schult T & Brandt S. Predicting Nerve Root Pathology With Voltage-actuated Sensory Nerve Conduction Threshold. The Internet Journal of Anesthesiology. 2002; Volume 6, Number 1.

Treating Piriformis Syndrome with Botulinum Toxin Using Pain Fiber NCS to Aid Diagnosis

Randall C. Cork, MD, PhD, Sarosh Saleemi, MD, Lou Hernandez, MD, Susan Brandt, MD, Rakesh Chaubey, MD and Lori Alexander, MBA, CPC.

Pain Management Clinic Dept of Anesthesiology, LSU
Medical School Health Sciences Ctr. Shreveport, LA

Piriformis Syndrome has been documented as a primary and/or contributory cause for sciatica and low back pain (1, 2, 3, and 4). Botulinum toxin-A TM is used by both medical and surgical specialists to successfully treat dystonic muscle disorders (6, 7, 8). During a seven- month period, 50 patients in our practice were diagnosed with piriformis syndrome and underwent intrapiriformis Botulinum toxin- ATM injection with remarkable pain relief at 6 to 8 weeks follow-up.

A retrospective review of 50 patients of the Pain Management Service at Louisiana State University Health Sciences Center who received intra-piriformis (Botulinumtoxin-ATM) injection was performed. All patients were taking one of the following analgesics: NSAIDS, Tramadol, or long acting opioids, or Gabapentin. All patients gave informed consent for this procedure. The demographic characteristics and relevant past medical histories of our study group are given in Table I and Table II respectively. Our diagnostic criteria for piriformis syndrome include the following: Gluteal pain with or without pain radiating down the affected leg in the distribution of sciatic nerve, muscle spasms/cramps/pull in leg muscles, positive Beatty's Maneuver (9) with or without the presence of tenderness, and L5, S1 or both L5 and S1 sensory nerve root hypoesthesia, as measured with the Neural-Scan voltage sensory nerve conduction device at 250 Hz (10) (26). Botulinum-toxin A (Botox, Allergan) is a preparation that comes in powder form. Botulinum toxin-ATM 100 units mixed in 5 cc of preservative-free normal (0.9 N) saline was used for each intrapiriformisinjection. Thefluoroscopictechniqueperformedisas follows: In a prone patient, the greater trochanter of the femur and the lower part of sacrum or sacroiliac joint of the same side is visualized, and a marker (e. g., a large hemostat) is placed on an imaginary line connecting the two. This represents the anatomical location of the piriformis muscle. Injection can be performed anywhere on this line, but the selected site was closer to sacrum where the base of piriformis muscle lies. Injections were made over bone to avoid possible injury to the sciatic nerve and pelvic structures. A 22-gauge 3.5inch spinal needle was advanced until the characteristic loss of resistance was felt as the needle penetrates the piriformis facial sheath. Omnipaque 1ml was then injected to obtain a piriformis myogram. After x-ray analysis showed negative for aspiration of blood, Botulinum toxin-ATM was then injected.

The outcome measures of pain intensity were Visual Analog Scales (VAS) (11), and modified McGill (12) scores, and the outcome measures of disability were Oswestry (13), and Roland-Morris Disability Scale (14) scores. The data below were obtained prior to treatment, and at 6-8 weeks follow-up after the procedure. VAS prior 0.151, compared to post treatment 0.242(p<0.05). Table III shows the change in McGill, Roland- study population were 8. 87 treatment (p<0.01). McGill scores were 40.6 3.04 before and 21.5 2.51 after the injection (p<0.01). Oswestry scores changed from 25.9 1.26 to 11.7 1.02(p<0.01) and Roland-Morris scores decreased from 16.0 0.935 to 20.6 1.02 (p<0.01). Lumbar Neural-Scan showed hypoesthesia in nerve roots L5 in 7/48, S1 in 9/48 and both L5 and S1 in 32/48 patients.
Botulinum toxin-ATM is a 150 Kda protein produced by Clostridium Botulinum. It is a neurotoxin, which acts presynaptically by inhibiting the release of acetylcholine, thus leading to functional denervation of muscle (15). This effect lasts up to 6 months. In 1989, FDA approved its use for the treatment of strabismus, blepharospasm, and hemifacial spasm (ref). Botulinum toxin-ATM has been on the market for a while now, but its use in pain patients has gained popularity only recently (16, 17, 18, 19). The piriformis muscle is a pyramidal muscle that arises as three digitations from the ventrolateral aspect of the sacrum from S1-S4, gluteal surface of ilium near the posterior inferior iliac spine and the anterior capsule of the sacroiliac joint. It passes through the greater sciatic foramen on its lateral trajectory to its tendonous insertion on anterior/medial aspect of the greater trochanter of the femur. Piriformis syndrome is a secondary cause of sciatica due to compression and/or irritation of sciatic nerve compressed by the contractedpiriformismuscle. Itssignsandsymptomscanbe explained by the proximity of the muscle to sciatic nerve at the sciatic notch. There are six possible relationships between the piriformis muscle and the sciatic nerve (23). Most commonly, the nerve is anterior and below piriformis muscle. The patient complains of pain, numbness and/or weakness in L4, L5 or S1 distributions. These may be associated with localized tenderness in piriformis muscle itself. Alternatively, pain due to piriformis spasm can also be felt as a deep, aching type of pelvic pain on the same side without signs and symptoms of sciatica.
As the piriformis muscle is a lateral rotator of hip flexion and assists in abduction, active muscle contraction can lead to pain reproduction (Beatty's maneuver (9). These physical signs if present are useful in differentiating piriformis syndrome, from sciatica due to other causes alone.
Neural-Scan is a direct sensory function test, which provides a reproducible (<0.2mA) functional assessment of the peripheral sensory nervous system by measuring the voltage intensity which initiates membrane potential changes, to propagate a nerve impulse. One problem with the diagnosis of the piriformis syndrome has been the lack of consistent objective diagnostic findings. We have found lumbar Neural-Scan tests reliable in detecting sciatica and, when correlated with signs and symptoms can confirm the diagnosis of piriformis syndrome.
Our study shows an association of piriformis syndrome with low back injury and/or surgery, degenerative disk disease, total hip surgery, spinal metastases and pelvic surgery. Two of our patients had piriformis syndrome after hard falls to the floor. We speculate that piriformis muscles may go into spasm either secondary to irritation of its nerve supply, sciatic nerve irritation, as in disk disease, lumbosacral radiculitis, or surgery in its vicinity, such as in total hip replacement, pelvic surgery, etc.
A variety of therapeutic approaches have been suggested for the management of piriformis syndrome (20, 21, and 22). These include conservative measures such as analgesics, application of heat, osteopathic manipulation, stretching exercises and even surgical resection of the piriformis muscle (23). Except for the latter, none of these modalities offer significant pain relief, and surgery is associated with morbidity. Perisciatic injection of steroids (24) and caudal epidural steroid injection for piriformis syndrome (25) have been described, as well as injection of local anesthetics and steroids in the muscle belly, but at present there are no outcome data which show their efficacy. Our study shows that intrapiriformis Botulinum toxin- ATM injection significantly reduces pain and disability for at least 6 and up to 8 weeks. All of the patients who underwent Botulinum toxin-ATM M injection to piriformis muscle reported at least a 45% reduction in pain as well as improvement in their disability scores. Intrapiriformis Botulinum toxin-ATM injection can be performed easily and quickly (< 10 minutes)...

Neural Scan Data

Transforminal ESI
Before Treatment Mean SEM


MCGILL 40.629 + 3.048 21.555 + 2.510 P <0.01
ROLAND MORRIS 16.074 + 0.935 11.740 + 1.021 P < 0.01
OSWESTRY 25.963 + 1.260 20.666 + 1.224 P < 0.01

Zia Durrani,MD, Alon P. Winnie, MD: Piriformis Muscle Syndrome: Under-diagnosed Cause of Sciatica: Journal of Pain and Symptom Management; Vol 6 No. 6, August 1991.
Pace, J. B., and Nagle, D: Piriformis Syndrome. Western Journal of Medicine: 124:435-9, June 1976.
Hallen R. P.: Sciatic Pain and Piriformis Muscle Syndrome. Postgraduate Medicine: 1983:74:69- 72.
John R. Parziale, MD, Thomas H. Hudgins,MD.: The Piriformis Muscle Syndrome. The American Journal of Orthopedics, December 1996.
Retzlaff E. W.: The Piriformis Muscle Syndrome. The Journal of American Osteopathic Association: 1974 Jun; 73(10): 799-807.
Joseph Jankovic, MD,: Therapeutic Uses of Botulinum Toxin: The New England Journal of Medicine: April 25, 1991.
Joseph K. C. Tsui: Botulinum toxin as a therapeutic agent: Pharmacological Therapeutics: 1996: 72(1): 13-24.
N. Mahant MBBS FRACP: The current use of botulinum toxin. Journal of Clinical Neuroscience: 2000 Sept: 7 389-94.
Beatty R. A.: The piriformis muscle syndrome: A Simple Diagnostic Maneuver. Neurosurgery: 1994; 34: 512-4
Cork, R. et al: Single-Electrode Current Perception Threshold (V-sNCT) and Nerve-Root Pathology: Regional Anesthesiology and Pain Medicine Vol. 24 No 3 May 1999
Scott, J and Huskisson, EC: Graphic Representation of Pain. Pain: 2 (1976) 175-184.
Ronald Melzack: The McGill Pain Questionnaire. Pain: 1(1975) 277-299.
Jeremy C. T. Fairbanks, FRCS et al: The Oswestry Low Back Pain Disability Questionnaire: Physiotherapy, 1980; 66:271-273.
Roland M., Morris R.: A Study of the Natural History of Low Back Pain - Part I: Development of a Reliable and Sensitive Measure of Disability in Low Back Pain. Spine: 1983:8; 141-144.
P. Hambleton: Botulinum Toxin: Structure and Pharmacology. Eur. Arch of Oto-Rhino- Laryngology: Supp: 1994: S 200-2.
William P. Cheshire: Botulinum Toxin in the Treatment of Myofascial Pain Syndrome: Pain 59(1994) 65-69.
Barry M. Guyer, MA, and MB: Mechanism of Botulinum Toxin-A in the relief of chronic pain. Current Review of Pain: 1999, 3:427-431.
Mauro Porta: A Comparative Trial of Botulinum Toxin-A and Methylprednisone for the Treatment of Myofascial Pain Syndrome and Pain From Chronic Muscle Spasm: Pain 85 (2000) 101-105.
Jose J. Monsivais, MD, FACS: Botulinum Toxin in Painful Syndromes: Hand Clinics: Vol. 12. No. 4 November 1996.
Wyant G. D.: Chronic Pain Syndromes and Their Treatment III. The Piriformis Syndrome: Canada Anesthesiology Society Journal: 1979:26:305-308
Pamela M. Barton: Piriformis Syndrome: A Rational Approach to Management: Pain 47(1991) 345-352.
Carles Steiner, DO, FAAO et al: Piriformis Syndrome: Pathogenesis, Diagnosis and Treatment. The journal of American Osteopathic Association: 87(4): 318-23. April 1987
Ludvig Fjeld Solheim: The Piriformis Muscle Syndrome; Sciatic Nerve Entrapment Treated with Section of the Piriformis Muscle: Acta orthop. Scand. 52, 73-75,1981.
M. Hanania: Perisciatic Injection of Steroid for the Treatment of Sciatica Due to Piriformis Muscle Syndrome. Regional Anesthesia & Pain medicine: 1998 Mar-Apr: 23(2): 223-8
Vildan Mullin, MD and Michael Rosayro, FFARCS: Caudal Steroid Injection for Treatment of Piriformis Muscle Syndrome: Anesthesia/Analgesia 1990;71;705-7.
Cork, Randall, PhD. MD., et al: Predicting Nerve Root Pathology With Voltage-actuated Sensory Nerve Conduction Threshold. Internet Journal of Anesthesiology: Nov. 2002

Pain Fiber NCS Objectively Supports and Quantifies Subjective Pain

Presented: American Academy of Pain Medicine San Diego February 2006 Abstract Form Category: Research - Clinical
Sensory A-delta fiber nerve conduction testing discriminates mild from severe chronic spine pain
Abstract Text:
Objective validation of the complaint of pain is a major problem in treating chronic spinal area pain, and chronic pain in general. While patient symptom description and imaging studies help to refine pain assessment, there is need for an objective test of pain perception, and measurement of pain magnitude.

In our study, we correlated sensory A-delta fiber nerve conduction testing with clinically determined mild and severe pain levels reported in patients with paraspinal pain. Two groups of 40 non-compensation patients were categorized as having mild or severe pain based upon a scoring system. Subjective symptoms, range of motion measurements, pain inventories, imaging studies, employment status, drug seeking behavior, and use of medications were assessed in determining an overall picture of pain severity. Sensory nerve conduction tests were done. The abnormalities were added to arrive at a score. Patients with mild pain had a mean score of 9 and those with severe pain had a score of 30. A chi square analysis of the results, indicated that the A delta combined scores correlated with pain severity at a p level < 0.01.

We found that sensory nerve conduction testing is a useful objective parameter in the evaluation of chronic spinal pain. This test is very inexpensive for patients, non-invasive, and a potential avenue for routine evaluation of chronic paraspinal pain.

Authors: Alex Ambroz, MD: Clinical Assistant Professor, Marshall University School of Medical

Robert Odell, MD, PhD: MD and PhD Biomedical Engineering Stanford Med School

Sacral Entrapment Syndrome
Chronic Prostatitis

Nerve Root Pathology

Nerve ID

ROC Curve

Nerve Roots

Dr.Cork, pf-NCS

Chapter VII   -   Table of Contents   -   References