Neurometer^® CPT
Frequently Asked Questions (FAQ)

	What are NEUROMETER® CPT devices?
	How is the sNCT/CPT procedure conducted?
	How long does it take to perform the sNCT/CPT procedure?
	What specific information does the procedure provide?
	How does the sNCT/CPT evaluation assist in clinical evaluations?
	How does the sNCT/CPT exam compare to other neurodiagnostic procedures (sNCV, SSEP, EMG, MRI)?
	What are the indications for performing the sNCT/CPT examination?
	How much training is required to properly perform the procedure?
	What type of training is required to evaluate CPT measures?
	How is the test result (sNCT/CPT) data interpreted?
	Is the sNCT/CPT exam an objective or subjective procedure?
	What other types of procedures can Neurometer® CPT devices perform?
	Are there any publications reporting on the Neurometer® CPT procedure?
	What health insurance codes are commonly used by the Neurometer® CPT electrodiagnostic evaluation?
	The Medi-Dx 7000 claims to perform a test like Neurometer® CPT devices. Is it true?

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Neurometer^® CPTs are electrodiagnostic devices which perform automated neuroselective sensory nerve conduction threshold (sNCT) evaluations by determining painless current perception threshold (CPT) levels. Using microprocessor controlled, neuroselective electrical stimuli, they quickly and painlessly quantify the conduction and functional integrity of the large and small myelinated and small unmyelinated sensory nerve fibers at any cutaneous site. CPT measures can detect and quantify early stage neuritis as well as peripheral sensory neuropathy.
Neurometer^® CPT devices generate three different constant alternating current sinusoid waveform stimuli at 2000 Hz, 250 Hz and 5 Hz. Stimulus output intensities range from 0.01 to 9.99 mAmperes (mA). The constant current output assures highly reproducible measures which are unaffected by variables such as skin thickness, temperature or edema. The device's built in microprocessor is capable of performing both single-blind and fully automated double-blind examinations. Other device functions include an automated electrode cable and system integrity determination and a continuous monitoring of stimulus output parameters and battery charge levels with appropriate warning alarms and messages. A printer may be used in conjunction with the CPT/C device to permit direct paper recording of CPT evaluation data. Both the printer and the CPT unit are powered by the device's built in rechargeable battery.
Neurometer CPT^® devices are currently being employed for non-investigational, clinical purposes at thousands of locations around the world, including clinical, research and industrial settings. Use of the neuroselective sNCT evaluation has been taught in accredited Continuing Medical Education courses by the American Academy of Neurology, the American Association of Electrodiagnostic Medicine and numerous other national and international professional medical associations and institutions since 1985.
Neurometer CPT^® devices are prescription devices and U.S. Federal law requires that they be limited to use only by or under the order of a physician or other appropriate medical personnel. Permission to market CPT devices was granted by the F.D.A. in 1986. To date, more 1 million Neurometer^® CPT sNCT examinations have been performed.

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The Neurometer^® CPT sNCT electrodiagnostic examination employs a standardized, automated procedure to generate objective, quantitative measures of the conduction and functional integrity of sensory nerve fibers. The unit emits non-aversive transcutaneous electrical stimuli through a pair of gold plated electrodes to quantify neuroselective CPT values. The procedure includes testing the patient at one or more body sites with three different sinusoidal frequencies of electrical stimulus. Each frequency, 2000 Hz, 250 Hz, and 5 Hz, evokes a response from a different subpopulation of sensory nerve fibers, i.e. large myelinated, small myelinated and small unmyelinated fibers, respectively. Normative ranges of CPT values have been established and published for measures taken at multiple body sites and are used to analyze patient measures. Software included with each device can be used to analyze the data and print a report summarizing the results. The following is a brief description of the standard sNCT/CPT examination.
The CPT unit is situated with its controls placed out of view of the patient. The technician turns the unit on and conducts a Pre-Exam Cable Test by following directions displayed on the unit's Liquid Crystal Display (LCD) screen. Successful completion of this test confirms the proper functioning of the CPT unit, electrodes and cables prior to each examination.
The patient is placed in a comfortable position - sitting or reclining - and preferably in a location with minimal distractions. The examination procedure is explained to the patient. The prescribed skin sites to be evaluated are examined to confirm that the skin is intact. The skin may be cleaned and prepared for testing using a skin prep-paste. A pair of 1 cm. diameter disposable gold electrodes are coated with a thin layer of conductive gel and then taped to the test site.
The patient is first presented with an Intensity Alignment procedure which quickly narrows down the threshold level to a range of +/- 50 µAmperes out of a total range of 0 to 9.99 mAmperes. Next, the patient begins the Auto Test Mode which is a fully automatic, double-blind, forced choice procedure to determine the actual Current Perception Threshold measures. The patient is presented with randomly generated pairs of real and placebo stimuli which they are then asked to identify verbally or by pressing or releasing a button on a remote unit. Based upon the patient's response, the CPT device adjusts the output level of the stimulus and randomly generates a new testing order for the next pair of tests in the series. The automated design of the sNCT/CPT testing procedure assures that neither the patient nor the operator can influence the test outcome based upon subjective impressions. When a sufficient number of tests have been performed (p<0.006), the CPT device determines and displays the CPT value for the test series and optionally prints out the results. The Auto Test Mode follows a testing paradigm similar to that used in standard auditory tests and can determine the patient's CPT measures to within +/- 20 µAmperes. Compliance Guard™ technology monitors patient responses for consistency and accuracy. This testing sequence is repeated for each of the three frequencies of stimulus before moving on to the next body site.

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The average time needed to perform a three-frequency test at single site test is approximately 10 minutes. Keep in mind, however, that each test is equivalent performing three different neurodiagnostic procedures, since the Neurometer^® CPT procedure independently evaluates all three major subpopulations of sensory nerve fibers comprising more than 90% of the typical sensory nerve. All other neurodiagnostic procedures measure only a single subpopulation of fibers - typically the large myelinated fibers which only make up around 10% of a sensory nerve. A typical evaluation may involve testing 2 to 6 sites (1 to 3 sites bilaterally) making the total time for a test approximately 20 to 60 minutes. The Neurometer^® CPT/C, NervScan NS3000 and NervScan 2000 also feature a Ranged CPT (RPCT) mode that can perform three independent neuroselective tests on a nerve in about three minutes.

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The equipment performs sNCT evaluations by determining neuroselective sensory Current perception Threshold (CPT) measures. CPT measures are objective, quantitative determinations of sensory nerve conduction and functional integrity which are obtainable from any cutaneous site. Each CPT measure represents the minimum amount of a painless, neuroselective, transcutaneous electrical stimulus required to reproducibly evoke a sensation approximately 50% of the times it's presented. Three independent CPT measures are obtained from each test site by using three different sinusoidal frequencies of electrical stimuli: 2000 Hz, 250 Hz and 5 Hz. These measures selectively quantify the functioning of the three major sub-populations of sensory nerve fibers providing innervation to the test site: the large myelinated, small myelinated and small unmyelinated fibers. Abnormally low CPT measures indicate a hyper-sensitive nerve function (commonly associated with inflammation or neuritis) reflecting a hyperesthetic condition. Abnormally elevated CPT measures indicate a loss of nerve function reflecting a hypoesthetic condition or neuropathy.
CPTs are measured in units equivalent to 0.01 mAmperes (mA) of output intensity. At output intensities below 0.10 mA, CPT measures are resolved in increments of 0.1 CPT units (1 µAmpere). For example, a CPT measure of 100 indicates a stimulus output intensity of 1.0 mA; a CPT of 9.5 indicates an output intensity of 0.095 mA. The stimulus output range of the CPT device is 0.001 mA (CPT=0.1) to 9.99 mA (CPT=999).

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Differential Diagnosis: The Neurometer^® CPT sNCT evaluation is used to objectively quantify sensory nerve function when the history (sensory symptoms) and physical examination (abnormalities desp;   The differential diagnosis of sensory neuropathy can include: radiculopathy (disc injury), compressive lesion (e.g., carpal or tarsal tunnel syndrome), as well as axonal versus demyelinating polyneuropathy (e.g. Guillian-Barré Syndrome, diabetic, uremic, alcoholic, toxic), spinal impairment or other types of central nervous system dysfunction (e.g. syringomyelia). Different sensory nerve pathologies can exhibit distinctly different distributions of sensory impairment and may selectively effect the functioning of specific sub-populations of nerve fiber function (e.g. demyelinating neuropathies or large versus small fiber dysfunction). For instance, the impairment resulting from radiculopathy will be confined to a dermatomal distribution whereas the impairment from polyneuropathy secondary to axonopathy is most often confined to a distal distribution, involving primarily the toes, fingers and multiple nerves. CPTs can be mapped from any cutaneous location in order to assist in identification and diagnosis. Patients may also have a combination of sensory neuropathies such as an alcoholic with "Saturday Night Palsy", a diabetic with radiculopathy or a uremic with carpal tunnel syndrome superimposed on polyneuropathy.
The objective nature of the Neurometer^® CPT sNCT exam can also help in determining if a patient has sensory neuropathy consistent with their reported symptoms or if instead they might be suffering possible non-neurological impairments or seeking secondary gain. Conditions such as vascular or soft tissue lesions or arthritis, a ligamentous sprain or muscular sprain which can include symptoms of radiating pain, may mimic neuropathic conditions. For these reasons, it is sometimes necessary to conduct the automated sNCT evaluation in patients with complaints of radiating pain to confirm the differential diagnosis in order to prescribe appropriate treatment.
Determining Clinical Severity: The Neurometer^® CPT sNCT evaluation objectively documents the clinical severity of neurogenic abnormalities. The evaluation measures whether the impairment is early stage neuritis (hyperesthesia or nerve inflammation) versus late stage neuropathy, hypoesthesia (loss of function) or anesthesia (complete loss of sensation). Serial mapping of the distribution of impairment permits the assessment of the progression of disease. This information guides the clinician's decision for the most appropriate treatment and/or medical/surgical referral. Generally, the earlier the therapeutic intervention the better the prognosis.
The Neurometer^® CPT sNCT evaluation enables physicians to evaluate those sensory fibers which mediate both pain and non-pain sensation. Both types of fibers should be evaluated because disease conditions may selectively impair large fiber function (position and vibratory sense) and/or smaller fiber function (pain and temperature). The evaluation of small fiber function is also critical for assessing protective sensation.
Monitoring Therapeutic Intervention: The CPT evaluation is also used to monitor the efficacy and gauge the outcome of therapeutic intervention by providing objective serial measurements of the neuropathy, disability and neuro-regenerative processes. The painless nature of the test ensures high patient compliance for follow-up examinations.

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There are numerous publications comparing the sensory nerve conduction threshold (sNCT/CPT) exam to traditional nerve conduction velocity studies, and they generally demonstrate a strong correlation between both their findings and levels of reliability. Several studies comparing sNCT/CPT to MRI evaluations have demonstrated similar levels of correlation. While the CPT test does have much in common with other neurodiagnostic procedures, these studies also pointed out specific areas in which its capabilities surpass those of the other procedures. It is a non-aversive measurement and patient compliance with serial testing is extremely high. It is also relatively insensitive to changes in skin temperature, thickness, scar tissue or edema which can distort or block the measures from other types of exams. The test is neuroselective for large myelinated, small myelinated and unmyelinated sensory fibers. It is a functional evaluation that can be performed at early stage neuritis or late stage neuropathy, and healthy control CPT values are available for measures of the shortest afferents on the face to the longest afferents on the toe. The Neurometer^® CPT device is extremely safe, battery powered, and easy to use.
The sNCV and SSEP tests evaluate the large diameter myelinated sensory nerve fibers, which typically comprise less than 10% of a peripheral nerve. Conditions which selectively effect the smaller nerve fibers are undetectable by these tests. The CPT evaluation measures the conduction and functional integrity of all three major sub-populations of sensory nerves fibers, including the large myelinated, small myelinated and unmyelinated fibers. Together, these make up more than 90% of the sensory fibers in a typical nerve. Many conditions, particularly in the early stages, selectively effect a specific sub-population of fibers while leaving the other fibers untouched. The sNCT/CPT test is indicated for neuropathologies effecting large and/or small sensory fiber pathology.
The sNCV and SSEP tests are limited to measuring reductions in amplitude or conduction velocity resulting from a significant loss of nerve function. The sNCT/CPT evaluation is not limited to evaluating only those conditions which result in a significant loss of nerve function since it detects and quantifies hyperesthesia as well as hypoesthesia. Hyperesthetic conditions reflect inflamed or irritated sensory nerve fibers that have not yet lost their functioning (i.e. become hypoesthetic). Hyperesthesia occurs before hypoesthesia or anesthesia in progressive peripheral nerve damage. Detection of hyperesthesia allows for earlier medical therapeutic intervention in a disease condition with the potential of limiting more severe damage. The ability to quantify the functioning of the smallest unmyelinated afferents also makes sNCT exam capable of detecting most types of peripheral nerve regeneration unlike the other procedures.
The needle EMG test and motor nerve conduction velocity (mNCV) tests only provide information about motor nerve innervation and muscle function. These tests provide no information about sensory nerve function. The automated sNCT evaluation only provides information about the sensory nerves. Sensory nerves are usually effected at an earlier stage than motor nerves in most common types of progressive neuropathology.
The sNCT/CPT evaluation is also capable of monitoring recovery of sensory nerve functional integrity following carpal tunnel release, nerve repair or treatments such as plasmapheresis or immunoglobulin therapy. All of these therapeutic interventions result in scar formation which causes an artifact that impairs physiological measures such as the sNCV or the SSEP.
The CPT evaluation is indicated in the early stages of suspected radiculopathy, instead of a needle EMG, to perform an objective evaluation of the patient's condition and ascertain the efficacy of therapeutic intervention. In the case of a compressive radiculopathy from, for example from a bulging disc, Wallerian degeneration is required before a needle EMG will show any abnormal findings. This degeneration typically requires three to six weeks to occur before the needle EMG can document this impairment which can result in a delay in the application of effective therapeutic intervention. The sNCT/CPT evaluation has been shown to be capable of documenting immediate changes in spinal nerve function. Various publications have demonstrated the effects of spinal lidocaine and narcotics on CPT measures within minutes of administration.
The sensory nerve conduction velocity (sNCV) evaluation tests only a small segment of a peripheral nerve - typically less than 50 cm on an arm or a leg. With most radiculopathies sensory nerve conduction is impaired by an injury of the spinal nerve roots and do not effect peripheral sNCV measures (e.g. from the arms and legs) which are completely insensitive to this condition. The automated sNCT/CPT evaluation is sensitive to an impairment of sensory nerve function occurring anywhere between the nerve test site and the cortex. Studies have documented the ability of the CPT measure to evaluate the sensory abnormalities resulting from a radiculopathy as well as the loss of sensory nerve function resulting from spinal pathology, spinal anesthesia and analgesia.
The sNCT/CPT evaluation may also be a test to be considered instead of the MRI for certain patients, not only because of the financial savings, but primarily to help improve the quality of patient care. According to the 1994 publication by Jensen, et al from the New England Journal of Medicine, Volume 331, No. 2, pages 69-73 titled "Magnetic resonance imaging of the lumbar spine in people without back pain", the MRI evaluation has a tremendously high number of false positive findings yielding erroneous diagnostic interpretations (disc herniations without symptoms). The MRI is a structural and not a functional test - and as such is insensitive to inflammatory conditions such as disc irritation or nerve root irritation which may result in hyperesthesia within a dermatomal distribution but not effect MRI imaging findings (i.e. an unremarkable or normal MRI). The CPT evaluation has the unique ability to detect hyperesthetic conditions thereby confirming the pathology exists. Knowledge of this condition is used to guide the physician in determining the most effective therapeutic intervention and may also assist in patient education.

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The CPT/sNCT test is indicated in any patient with a presumptive diagnosis of sensory nerve dysfunction. Peripheral sensory nerve impairments have four major categories: poly-neuropathy, radiculopathy, compressive neuropathy and focal nerve lesions. The sNCT test is used to identify and localize areas of abnormal function, to determine the severity of the abnormality and to aid in diagnosis, prognosis, guiding and evaluating treatment. The following is a partial list of those conditions associated with neuropathology that may be evaluated by the CPT/sNCT evaluation:

Metabolic: Uremic, hepatic, thyroid related, diabetes and other endocrine disorders.

Compressive or Traumatic: Carpal and tarsal tunnel syndrome, thoracic outlet syndrome, brachial plexopathy, radiculopathy, vibration neuropathy and focal nerve lesions.

Toxic: Ethanol, heavy metals (such as lead), arsenic, acryl-amide, organophosphate (pesticides), PCBs, trichloroethane, organic solvents and antineoplastic chemotherapeutic agents.

Acquired: HIV, Lyme disease, Hansen's disease (leprosy), post herpetic neuralgia.

Hereditary and Others: Charcot Marie Tooth, Laurence Moon Bidal, Freidricks Ataxia, Multiple Sclerosis, Vitamin B12 deficiency, reflex sympathetic dystrophy (RSD) or Complex Regional Pain Syndrome (CRPS), neuroma, regeneration, ruling-out psychogenic (hysterical sensory loss), neuropathy of cancer, COPD associated neuropathy, high altitude neuropathy, syringomyelia, cerebral vascular accident related sensory loss, and immune mediated sensory dysfunction (e.g. neuropathy associated with Anti-Myelin-Associated Glycoprotein Antibodies).

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Technicians can be trained in less than a day by a qualified sales representative, and there are manufacturer's technical certification courses available. A manual detailing the examination procedure is included with each device.

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Any licensed physician can interpret the results of the sNCT/CPT test procedure by using the data generated by the NEUVAL^® CPT data analysis software in conjunction with other clinical data and impressions of the patient. The location and distribution of the CPT abnormalities on the patient (if present) can help the physician corroborate a diagnosis made based on history and physical examination findings. A manufacturer's clinical certification course is offered to physicians and provides training by a board certified physician on the clinical use of the sNCT/CPT test and the interpretation of the results of the test.

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The NEUVAL^® CPT evaluation and database software, included with each CPT device, evaluates and stores a patient's CPT values and generates a report detailing the condition of the nerves tested. These evaluations are based upon comparisons with standardized ranges of healthy CPT values and ratios included in the software. Both the CPT values and their ratios are considered when determining the degree of sensory nerve impairment and both contribute to the overall neurological diagnosis. The data analysis may include a determination of hyperesthetic and/or hypoesthetic conditions. Normative data is provided for more than thirty different test sites. All normative sNCT/CPT values employed are either published in peer reviewed journals or available for review. They are not confidential.
Most importantly, as with any neuro-diagnostic test, a clinician's interpretation including a clinical correlation is essential and necessary for diagnostic purposes.

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The Neurometer^® CPT sNCT examination is an a objective test for quantifying the functional integrity of sensory nerve fibers. The sNCT/CPT procedure is based on the same objective paradigms used for evaluating hearing and vision. These methodologies are widely used, well characterized, and legally recognized.

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The Neurometer^® The Ranged CPT (RCPT) mode which enables individuals or large groups to be evaluated in only minutes. The CPT/C also has a Pain Tolerance mode which allows a reproducible, non-invasive and atraumatic method for measuring Pain Tolerance Threshold (PTT) levels in small and large fibers (if present) for evaluation of the patient with pain. Some CPT/C devices include an animal response test (ART) mode which permits atraumatic neuroselective sensory evaluations of animals for laboratory investigations.

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There are hundreds of peer reviewed publications which report on the Neurometer^® CPT evaluation. These studies address issues ranging from the clinical utility and reliability of the procedure to the neuroselective nature of the stimulus. They include publications from over 40 national and international medical organizations spanning more than 16 different medical and surgical specialties. A bibliography listing hundreds of additional references of peer reviewed publications describing the application of painless and painful electrical stimulation for quantifying sensory nerve functions is available.

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Various countries have established health insurance procedure codes for the Neurometer^® CPT electrodiagnostic evaluation. In the United States, codes may vary by to state and within a state as well. Billing codes have been established for various states including: Texas and Massachusetts Workers' Compensation Commissions as well as the Department of Labor and Industry in Washington state. A Neurometer^® CPT product literature document describing the billing codes in the USA for the sNCT procedure is available by clicking here.

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No, it is a fraudulent claim by the manufacturer of the Medi-Dx. The Medi-Dx does not use a neuroselective stimulus so it can not independently evaluate different type sensory fibers and it does not have a constant current output so there is absolutely no way to make accurate or repeatable measures. There are also no peer reviewed articles that examine or validate the type of test performed by the device. Click here for additional information, including an Engineering Report documenting the differences between the two devices.

Modified 08/26/05.
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