Neurometer® CPT® Comparison to Other Diagnostic Procedures Chart

Sensory Diagnostic Procedures

Neurometer: s-NCT/CPT – Neurometer Sensory Nerve Conduction Threshold / Current Perception Threshold

sNCV: sensory Nerve Conduction Velocity

Skin Punch Biopsy

SSEP: Somato Sensory Evoked Potential

Thrm: Thermal Threshold (hot/cold)

Vib: Vibratory Threshold

FeatureNeurometer sNCV Skin Punch Biopsy SSEP ThrmVib
Selectively evaluate large myelinated fibers
Selectively evaluate small myelinated fibers
Selectively evaluate unmyelinated fibers
Evaluate hyperesthesia
Evaluate hypoesthesia
Measure early nerve regeneration
Measure advanced nerve regeneration
Measure & Map metabolic/toxic dying back polyneuropathy from tips of toes & fingers
Evaluate compressive neuropathy e.g Carpal Tunnel Syndrome
Evaluate radiculopathy (1)
Localize and evaluate focal nerve lesions
Test any cutaneous site
Unaffected by skin thickness or edema
Unaffected by normal ambient or skin temperatures
Double-blind automated procedure
Automated confirmation of patient test procedure compliance N/AN/AN/A
Employs a standardized testing methodology
Allows nerves to serve as their own controls
Standardized clinically established validated ranges of healthy measures
Painless high compliance procedure

(1)Sensory NCV Insensitivity to Radiculopathies: References
a. Electrodiagnosis in Clinical Medicine. 2nd edition, edited by Michael J, Aminoff, Churchill Livingstone, New York, page 300 1986. Dr. Aminoff is the editor of Muscle & Nerve. Page 300 states:“…radiculopathies usually are not associated with changes in nerve conduction [velocity] studies…Because most lesions of the spinal nerve and nerve root occur proximal to the dorsal root ganglion, the sensory potentials are usually normal, even in the distribution of a sensory impairment.”
b. Kimura, J. Electrodiagnosis in Diseases of Nerve and Muscle. Edition 2, page 448, F.A. Davis Co. Philadelphia., PA, 1989.
c. Goodgold, J. Rehab. Medicine. page 53, C.V. Mosby Co. St. Louis, MO, 1988.

Numerous publications compare the sensory nerve conduction threshold (sNCT/CPT) exam to traditional nerve conduction velocity studies and generally they demonstrate a strong correlation between both tests findings and levels of reliability. 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, CPT studies also a lso surpass other procedures in it’s being an non-aversive measure that enhances patient compliance for serial evaluations.  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 (eg., NCV). The test is neuroselective for large myelinated, small myelinated and unmyelinated sensory fibers. It is a functional evaluation that can evaluate 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 sensory Nerve Conduction Velocity (sNCV) and Somato-Sensory Evoked Potential (SSEP) tests evaluate the large diameter myelinated sensory nerve fibers, which typically comprise less than 10% of a typical 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, myotomal 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.