Physiology: How Pain Fiber Nerve Conduction Studies (pf-NCS) Works
Without the AXON-II 43% of pain patients develop chronic symptoms and over 50% of back surgeries end in failure.
The following statement concerning the severe limitations of conventional EMG/NCV appeared in a State-Of-The-Art-Review Titled: "EVALUTATING RADICULOPATHY: HOW USEFUL IS ELECTRODIAGNOSTIC TESTING?" in the journal Physical Medicine & Rehabilitation Vol. 13, No.2. Page 251: "In chronic cases, particularly in individuals with predominantly sensory symptoms, it is difficult or impossible to clinically estimate the type or severity of nerve injury. Only if there is obviously muscle atrophy can one know for certain that motor axon degeneration has occurred." Page 254: "Most conventional sensory and motor studies are normal when evaluating nerve root dysfunction... because the compressive lesion is proximal to the dorsal root ganglion (DRG)."
Patients and even some physicians are under the mistaken impression that EMG/NCV can test all types of nerve fibers. To be clear, conventional EMG (electrical muscle graph) and NCV (nerve conduction velocity) tests cannot assess pain nerve fibers, which explains why 43% of patients seeking medical help for pain end up with chronic symptoms. The Massachusetts General Hospital Handbook of Pain Management (2005) explains that "EMG/NCV cannot test small pain fibers." and "In most cases (over 50%) of neck and back pain the anatomic and pathologic diagnosis remains unclear." The textbook Neurology For The Non-Neurologist by Weiner & Goetz (Lippinott 2005) states: "EMG/NCV in the absence of motor deficit (muscle weakness or atrophy), is costly, time consuming and seldom benefits the patient."
The only electrodiagnostic test that assesses pain nerve fibers is the pf-NCS.
GUYTON & HALL TEXTBOOK OF MEDICAL PHYSIOLOGY
Guyton explains why 50% of patients misdirect doctors away from the source of pain:
Over 90% of signals transmitted by the (Fast Pain) A-delta fibers reach the sensory cortex, so they should allow the patient to exactly localize the source of pain. However, soon after an injury A-delta fibers become numb, while the poor localizing C-Type fibers up-regulate. Regarding this Guyton states: "It explains why so many patients have serious difficulty in localizing the source of some types of chronic pain." What types of pain? The most common types – neck and back pain. Patients do not have difficulty localizing the source of their pain, they simply localize it to the wrong nerve root level. Nearly 20% will localize to the wrong side.
The pf-NCS tests all the major peripheral nerves to detect down-regulated A-delta function. The patient is his own control, so statistical sensitivity approaches 100%. The patented electrical signal selectively stimulates A-delta fibers, so the nerve requiring the highest voltage amplitude to cause an A-delta action potential detects pathology. The pf-NCS is objective, since a potentiometer detects the amplitude of the action potential that verifies firing. This is independent of the patient’s psychophysical (perception) of a sensation. Since the patient acts as the control, the test is unaffected by age, gender or population variables. The AXON-II can also be used to test (Slow Pain) C-Type and (Light Touch) A-beta fibers, which can be useful when RSD or sympathetically mediated pain syndromes are suspected.
Physician pf-NCS Certification
The Practice Guidelines found on the American Association of Sensory Electrodiagnostic Medicine (AASEM) web site (www.sensorymedicine.org) matches the April 2002 AMA Electrodiagnostic Examinations (EDX) Guidelines, which show that any physician can perform and supervise EDX procedures. The AASEM Practice Guidelines represent the consensus of physicians certified in the pf-NCS. To be clear, three points must be understood:
The AANEM (N stands for 'neuromuscular') represents physicians using conventional EMG/NCV and NCS of the large motor and one non-pain transmitting large sensory fiber in the S1 nerve. The testing of this single sensory nerve is based on a method developed in 1918 and it about as effective the Achillies Tendon Reflex.
Many patients and even physicians do not realize the 'M' in EMG stands for Myo = Muscle/Motor, and not 'Myelin' (fatty nerve covering) or 'myelo' (spinal cord). Only the (AASEM), a nationally recognized medical organization offering CME credit, represents physicians performing pain fiber nerve conduction studies (pf-NCS).
Physicians using the AXON-II should become certified in the pf-NCS through the AASEM a nationally recognized medical organization offering CME credit. The AASEM Practice Guidelines and Consensus of pf-NCS certified physicians supports that code 95904 is appropriate.
An increasing number of studies are being published and presented at scientific meetings. Two peer-reviewed studies can be found on the Internet Journal of Pain Symptom Control and Palliative Care (search: Cork v snct) Click on this page STUDIES and read recent researchers presented (Baddrodoja, Bush et al) in which they detected a relationship between chronic prostatitis and vulvadynia with L5 and or S1 radiculopathy. See News & Events and Studies.
In the spinal cord A-delta fibers synapse with motor neurons in the ventral motor pathway, so firing generates voltage directly from the A-delta fibers and sub-threshold voltage from the motor fibers. In minutes a nurse can test all the major nerves and their branches in a region - 18 (9 bilateral) in the cervical and 14 (7 bilateral) in the lumbar region. The nerve(s) requiring the highest voltage to fire identifies the injured nerve(s). Once the injured nerve is identified, testing proximal and distal to a suspected site of injury easily verifies the location.
For example; testing above and below both right and left medical elbows detects cubital tunnel entrapment. The non-symptomatic side acts as a control. Comparing median nerve branches in the fingers with the radial nerve (back of the hand) allows differentiation between carpal tunnel entrapment and nerve root pathology since the median and radial nerves originate from the same nerve roots, C6-7. The palmar branches of the median and ulnar nerve pass over the wrist, not through the carpal tunnel or Guyon's canal respectively, so palmar sites differentiate between proximal and wrist entrapments. The same differentiation is at works in the lower extremity where, like the cervical study, all the lumbosacral sites are proximal to sites of entrapment in the ankle. Any branch of a cutaneous nerve can be tested to map the dysfunctional area.
A-delta pf-NCS Efficacy Confirmed by Skin Biopsy
At the April 8-9, 2011 AASEM Annual Scientific Conference held in Baltimore Maryland, a Philadelphia neurological group reported on a series of 20 neck and back pain patients, all of which had negative EMG studies. However, the A-delta pf-NCS detected pathology that was confirmed by skin biopsy.
Though skin biopsy is widely held to be the gold standard for proving the existence of small pain fiber pathology, in many cases it fails to demonstrate small fiber loss in otherwise obvious pain cases. This is likely due to the fact that 50% of these pain cases have referred symptoms, which misdirect biopsies and treatments.
This series demonstrates that the A-delta pf-NCS detects pain fiber pathology that EMG-type tests cannot assess, and is as reliable as biopsy. Additionally, the A-delta pf-NCS is far more acceptable to patients than either needle EMG or skin biopsy.
Normal small fibers in a normal patient with a negative pf-NCS (demonstrated below)
Absence of small fibers in the dermatome of a patient with left L4 radiculopathy.
CRPS/RSD - SMP
Because the Axon-II tests the small pain fibers it can help detect signs of sympathetic dysfunction with pain caused by an otherwise innocuous stimulus. The minimum voltage intensity causing A-delta firing is normally painless, but in these patients the sensation may be painful suggesting sympathetic dysfunction.
In a study the Axon-II revealed pre-DRG pathology in many of these patients. Ten were available for one-year follow-up and all ten were free of all fibromyalgia symptoms.
Double Objective Proof
Pre-DRG pathology has been reported to correlate with abnormal vertebral motion as viewed on A-P lateral bending x-ray. This may be due to diminished sensory proprioceptive input affecting spinal motor function. The Axon-II has been reported in one study to be "a valuable aide in piriformis muscle syndrome diagnosis".
This website is not for general public use. It is meant for physician reference only. Nothing presented is meant to represent or imply use other than the FDA Indication and usage.
FDA Indications and Usage: The Axon-IITM NCSs is a diagnostic device that allows the quantitative detection of various sensory neurological impairments caused by various pathological conditions or toxic substance exposures. The subject population for whom this device can be used for diagnostic purposes includes any individual capable of communicating the perception of cutaneous sensation (with the potentiometer, which has a separate FDA clearance, the test is not dependent on the subject reporting perception of the cutaneous sensation, since the action potential of the nerve firing is detectable by the potentiometer). The Axon-IITM NCSs diagnostic examination may be conducted as part the neurological examination or for screening to detect peripheral neuropathies.
PainDx, Incorporated. gives permission to use documents on this web site provided that:
Documents from this site are for informational and non-commercial or personal use only. Such will not be copied or posted to any network computer or broadcast or published in any media or method now or hereafter developed, and
No modification of any document is made and no unauthorized purpose is prohibited by law. Violation may result in civil and/or criminal penalties.
Materials do not use the design or layout of the website.
INFORMATION ON PAINDX, INCORPORATED'S WEBSITE INCLUDING SPECIFICATIONS, APPEARANCE AND APPLICABILITY MAY BE SUBJECT TO CHANGE WITHOUT NOTICE. NO REPRESENTATIONS ARE MADE OR IMPLIED AS TO THE SUITABILITY OF THE INFORMATION ON THIS SITE FOR ANY PURPOSE. THE FULL CONTENTS ARE PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND AND ARE SUBJECT TO CHANGE WITHOUT NOTICE. ANY TYPE OF RISK WHICH MAY ARISE OUT OF USE OF THIS INFORMATION REMAINS WITH THE RECIPIENT. IN NO EVENT SHALL PAINDX, INCORPORATED BE LIABLE FOR ANY DIRECT, CONSEQUENTIAL, INCIDENTAL, SPECIAL, PUNITIVE OR OTHER DAMAGES (INCLUDING WITHOUT LIMITATION, DAMAGES FOR LOSS OF BUSINESS PROFITS, BUSINESS INTERRUPTION), EVEN IF PAINDX, INCORPORATED HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES.
All trademarks displayed on this website are subject to the U.S. trademark law, which support that any unauthorized use of trademarks is strictly prohibited.