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Tacticon^Ò Medical Enterprises, Inc.

Protocols For

Quantitative Sensory Testing Study Tacticon^Ò

(Tactile Circumferential Discrimination)  

 

(Registration information is at the end of the protocols)

   

April 28, 2001

For information on how to participate in the study, go to the end of the protocols

 

TABLE OF CONTENTS

I.  INTRODUCTION     2 

II. INSTRUMENTATION    3 

III.       TESTING DEVICE TO BE UTILIZED FOR THIS STUDY  3 

V. TESTING OF STUDY PATIENTS  4

       V.A.    Enrollment 4

V.B.     Pre-screening      4

V.C.     QST Testing Procedures  4

V.D.    Determining CDT      6

 VI.       UPPER EXTREMITY LEVELS    7

VII.     ABSTRACTS ON THE TACTICON^®  8  

The Tacticon ®

Charles Laudadio, MD, MBA

Stephen Freed, R.Ph., Diabetes Educator, Publisher

www.diabetesincontrol.com

email:  diabetesincontrol@home.com

 800-798-6972

 

 I.     INTRODUCTION

 In clinical practice, the onset and progress of diabetic neuropathy is assessed based on neuropathic signs and symptoms, including sensorimotor and reflex measures. These clinical measures generally lack inter-tester consistency, precision and reliability, leaving the subclinical neuropathy ­undetected. ­Most office based clinical sensory testing fail to discriminate between stimulus intensity and perception and depend on the qualitative assess­ment of both physician and patient, which is generally not well stan­dardized. A common test to assess vibration perception utilized an oscillating tuning fork placed over soft tissue or a bony prominence. Results are dependent on the force of the initial strike, the pressure applied to the tested area, the examiner's estimate of decay time, and the patient's perception that the stimulus is no longer present. Nega­tive symptoms, such as numbness, are particularly problematic since they are often insidious in onset, and patients with even moderate to severe involvement may remain unaware of the gradual sensory change.

This inability to quantify sensory impairment in an objective and reproducible manner across testers makes repeat assessments of individuals in longitudinal studies of peripheral neuropathy problematic.  For clinical studies, the reliability and validity of clinical measures must be known and have an acceptable level to able to detect small changes in a patient population over time. Reliabil­ity (reproducibility) of the test result must be consistent whether across patients or within a patient at each test visit even if performed different examiners. Reli­ability can be improved by using dichotomous measure­ments rather than continuous variables.  Thus the examiner can test for whether light touch or a tendon reflex are present or "absent" but assessing a relative scale such as "diminished" becomes much more subjective and tester dependent.  Conversely, the artificial compression of a continuous measurement into a dichotomous one may result in the loss of potentially valuable information.

Electrophysiology measures large-fiber function and, although objective and useful in determining a final diagnosis, is not practical for office based screening of patients for evidence of peripheral neuropathy. Thus, the limitations of clinical measures and electrophysiology necessitate the need for quantitative sensory testing using simple, cost effective, reliable and reproducible measures that are tester independent.

Quantitative sensory testing (QST) are procedures designed to provide accurate control of stimulus intensities to detect early impairment accurately and independent of testers.  The ability to assess treatment effects will mandate that testing of peripheral neuropathy be objective, quantifiable, easy to obtain, reliable, valid, inexpen­sive, and precise. Quantitative sensory testing uses instruments to control and deliver specific stimuli at specified intensities in order to test sensory thresh­old, defined as the minimal stimulus energy detectable 50% of the time. Sensitivity to vibration, temperature, and circumference discrimination is usually measured on the extremities of the feet since these are first afflicted.

QST is noninvasive, requires approximately 5-10 min­utes per test site, and can be administered by nonprofessional personnel after a brief training period. The hallmark of quantitative sensory testing is its ability to measure stimuli precisely, in microns of vertical displacement for vibration, in 0.1°C for temperature, and in mm for CDT in a way that are reproducible from trial to trial and from site to site and allow for trend, statistical analysis and an assessment of whether the magnitude of change is clinically meaningful. Such standardization is essential for the longitudinal assessment of patients.  Quantitative sensory testing makes use of psychophysical algorithms, which greatly enhance the sensitivity, and reliability of the threshold measurements.

Quantitative sensory testing is not a new concept. It has been a standard part of auditory assessments using audiograms to precisely quantify the magnitude of the hearing deficit in log units, or decibels, at specific frequencies. Assessment of somatosensory function, on the other hand, has his­torically been less quantitative, due primarily to the lack of devices capable of delivering stimuli of appropriate characteristics and intensi­ties. The relatively recent development of somatosensory QST methods and instruments has contributed significantly to the assessment of peripheral nerve function. The past decade has witnessed the development of portable and relatively inexpensive devices for quantitative sensory testing of vibration, circumference and thermal thresholds.

 

II.   INSTRUMENTATION

 

Circumferential discrimination testing is designed to measure larger, myelinated fiber integrity and mechanoreceptors utilizing a series of rods of progressively increasing circumference which when applied to the surfaces, provide exact assessments of fiber integrity which parallels that of vibration.

 

III.  TESTING DEVICE TO BE UTILIZED FOR THIS STUDY  

 

       Tacticon^® - Circumferential Discrimination Thresholds (CDT)

 

The Tacticon^® is an FDA approved device invented by Charles Laudadio, M.D. and validated by studies conducted at three separate institutions: Boulton¹ - (Manchester, England), Arezzo² - (Albert Einstein School of Medicine) and Maser, DeCherney and Laudadio³ - (Medical Center of Delaware and the University of Delaware).   The Tacticon^® quantifies the ability of human subjects to detect differences in the relative circumferences of different size probes applied to their distal extremities.  This test assesses the integrity of the distal mechanoreceptors and their enervation by large, myelinated nerve fibers.

 

The Tacticon^® consists of an anodized disk approximately ½ inch in thickness, 3.5 inches in diameter, and weighing approximately 6.5 ounces.  Protruding out from the circumference of the disk are eight metal probes (0-7) of increasing circumference from 12.5mm to 40mm.  Testing is achieved by rotating the disk and applying either the “0" rod or a larger rod, as determined by the randomization, to the patient’s extremity and asking them to identify the smaller probe using the accompanying QST algorithm.

 Purpose of Study:

 

Determine the sensitivity and specificity of the Tacticon^® by comparing the test scores with both the Monofilament and Tacticon^® in patients with diabetes who have no clinical signs or symptoms of neuropathy but are at risk of having subclinical neuropathy.

 

Objective of Study:

 

To determine the percentage of false negatives using the monofilament where subclinical neuropathy is present but the monofilament failed to detect it.

 

 

V.    TESTING OF STUDY PATIENTS

 

V.A.     Enrollment

 

Patient Enrollment Begins: May 1, 2001

Patient Enrollment Ends: July 1, 2001

Conclusions of Study: October 2001

Twenty doctors or educators will be provided the 5.07 monofilament, a Tacticon® device, and necessary forms.  Each doctor or educator will perform the study on a minimum of 25 patients.

 V.B.       Pre-screening

 The objective of this study is to enroll patients with non-clinically obvious peripheral symmetrical polyneuropathy due to diabetes.  Screening patients in the diabetes clinics for neuropathy study can be a very expensive and labor-intensive process if electrophysiology and full QST must be utilized for screening.  Screening can be accomplished more cost effectively by utilizing the Tacticon^® to obtain CDT (circumferential discrimination thresholds) which takes only 5 minutes per site. Conversely, patients can be tested with the monofilament cost effectively, however, many patients with subclinical neuropathy may be “missed”.  Early detection of neuropathy is important for instituting preventive measures (proper foot care, special shoes, etc.) to minimize the expensive sequelae of neuropathy (ulcers, infections, hospitalizations, amputations).

 

Patients found to have clinically significant neuropathy (loss of feeling, greatly elevated thresholds, etc.) should not be included in this study since their level of neuropathy can be easily diagnosed without the need for special QST testing devices and are already at high risk of complications.

 

       V.C.       QST Testing Procedures

 

Monofilament Testing

 

Patients will first be tested with the 5.07 monofilament, which is set to detect loss of protective sensation. This test is conducted first so as not to bias the tester with the actual level of neuropathy provided by the Tacticon^®.  The result will be recorded simply as “Yes” or “No” to the question  “Can You Feel This?”.

 

Tacticon^® Testing:

 

An instruction manual and scoring sheet will be supplied with the Tacticon, which will provide detailed instructions on testing.          

 

Testing of the toes should be performed on the anterior tip of the toe (not the bottom of the toe or behind the nail bed) since the bottom may have callus formation and the area behind the nail bed is not distal enough.

 

Thresholds should be reported as the Circumferential Discriminatory Thresholds (CDT) rather than probe number.  The CDT score is determined by first finding the rod level at which no errors were made when performing the two alternative forced choice algorithm with the accompanying randomization charts.  The conversion chart (attached) then provides the corresponding CDT, which is calculated by subtracting circumference of the reference rod (rod 0) from the threshold rod.

 

The algorithm recommended for use with the Tacticon^® was designed to determine the smallest difference in circumference, relative to the circumference of Rod 0, that could be reliably and consistently detected using an ascending and descending method of stimuli presentation and a "two alternative forced choice" response procedure. These methods have been recommended by the Panel on Quantitative Sensory Testing at the Neuropathy Assessment Conferences sponsored by the American Diabetes Association in 1988 and 1992.  Three errors were chosen as a good compromise between accuracy and speed of testing.

 

When performing the testing, explain the test to the patient so they understand what to expect and what you expect of them.  With them watching, gently apply two probes to their finger with just enough force to lightly blanch the skin and ask them if they can tell the difference in size.

 

The timing of rod presentation is standardized at approximately 2 seconds and the disk is pivoted by tester to easily bring different rods into contact with the skin surface.  Explain to the patient that when the real testing begins, they will be tested in a blinded fashion (blind-folded or testing masked from view) and on each trial they will be presented with two probes of different size and will be asked to tell you which one is smaller.  They must make a choice even when the test gets so difficult that they are guessing.

 

The tester, following the randomization provided on the scoring pads, begins testing with probe number 7.   Begin testing by using the numbers in column 1 of the scoring sheet corresponding to the probe (rod) level you have chosen to begin with.  The numbers for each set of trials are grouped in threes.  If the scoring pad indicates a “1" then probe “0" (the smaller probe) is presented first (1) and the larger probe is presented second.  If the pad indicates a “2", the large probe is presented first and the probe “0" is presented second (2).  As each probe is brought in contact with the skin, the tester says “number 1" or “number 2", “which probe was smaller?”.  If the patient responds correctly, put a diagonal stroke through the number and repeat the test using the next number in that group of three in the same column and row for that rod size.  If the patient correctly identifies the right probe on all three trials, move down the same column to the next row corresponding to the next smaller probe size and repeat the steps above.  Keep doing this until the patient makes a mistake.

 

When a patient gives an incorrect answer, stop testing at that probe level and put an “X” through that number instead of a stroke.  Restart testing now at the next higher row (next higher probe level from which the mistake was made) and move 1 column to the right.  That is, up one row and over one column. Repeat testing using the indicated groups of three until a second error is made and repeat the above.  When a third error is made, stop testing and identify the smallest row, which had no X’s (no errors).  This is the threshold. The Chart below gives two examples of a typical threshold.

Representative Scoring on a Patient Data Flow Chart

 

Rod #				Rod #
7				7
6	/ / /			6	/ / /
5	/ / /			5	/ / /		/ / /
4	/ / /			4	/ / /	/ / X	/ / X
3	/ / /	/ / /	/ / /	3	/ X
2	/ X	/ / X	/ X	2
1				1

                                                                                                Threshold = 5

                                                             / = correct               X = not correct

 

V.D.       Determining CDT

 

Once the probe threshold has been determined, it can be converted to “mm” which is the tactile circumferential discrimination level or the smallest difference in circumference a patient can detect. This is done by using the conversion chart below, which converts the probe threshold to CDT levels in “mm”.

 

CONVERSION CHART

 

    Circumferential Discriminatory Thresholds (CDT)

 

Lowest Rod Number w/o errors	Circumference of Rod (mm)	CDT (mm)
0	12.5
1	15.0	2.5
2	17.5	5.0
3	20.0	7.5
4	25.0	12.5
5	30.0	17.5
6	35.0	22.5
7	40.0	27.5
>7		32.5

 

Once a probe level and CDT have been determined, the chart below can be consulted to provide a relative severity score for that threshold which is affected by age.

Lower Extremity Levels of Neuropathy

 

Age Group

Neuropathy Classification

Rod #s

CDT (mm)