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Sensory Diagnostic Procedures
s-NCT/CPT
- Neurometer sensory Nerve Conduction Threshold / Current Perception
Threshold
sNCV -
sensory Nerve Conduction Velocity
Vib -
Vibratory Threshold
Thrm -
Thermal Threshold (hot/cold)
SSEP -
SomatoSensory Evoked Potential
Skin Punch Biopsy
(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.
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