Quantitative tests for neuropathic assessment - 1
Quantitative sensory testing (QST) is the determination of the absolute sensory threshold, defined as the minimal energy required to reliably stimulate the particular modality of sensation to be detected.
Quantitative tests for neuropathic assessment - 2
The higher the level of the minimal energy required the greater is the deficit of function of the particular modality of sensation.
Quantitative tests for neuropathic assessment - 3
In vibration threshold measurement the energy is delivered as voltage converted in the vibration of the probe. On VPT sensitometer, both voltage and vibration ie spatial disfigurement to and fro of the skin can be measured.
Quantitative tests for neuropathic assessment - 4
The higher the deficit of function the greater voltage is required, ie greater displacement for the limb to sense vibration.
Quantitative tests for neuropathic assessment - 5
The higher the deficit of function the greater voltage is required, ie greater displacement for the limb to sense vibration.Has great implications in prognosis and therapy.
Quantitative tests for neuropathic assessment - 6
QST is a relatively simple procedure that is both noninvasive and nonabrasive. In assessing diabetic neuropathy, the paramount concern is to detect the integrity of the axons forming the peripheral nervous system and their distal receptors.
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Measurable Modalities: Vibration Thresholds This measure is the most widely studied QST procedure. It principally assesses function in Meissner and Pacinian corpuscles and their associated large-diameter fibers.
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Vibration PerceptionThreshold is the indirectly made detection of loss of protective pain sensation that would render a patient susceptible to foot ulceration.
Other Measurable Modalities Light Touch: This measure tests the integrity of Merkel touch domes and Meissner corpuscles and their associated large-diameter fibers. Thermal Sensitivity: Known - Marstock Thermode The new system: Heat and Cold Perception Threshold
What do we have for Assessing NeuropathyNeed to assess associated risk of ulceration in a neuropathicNeed to distinguishNeuropathic and non neuropathic patientsNeed to establishwide range of quantitatedgradation of sensory deficitsfor comparison onFollow upSimple test equipments
Have it now
The ability to identify feet at risk of ulceration has been demonstrated prospectively in two studies using the biothesiometer.
[Young MJ, et al. Diabet Care 1994][Abbott CA, et al. Diabet Care 1998].In one study using the monofilament.
[Rith-Najarian SJ, Diabet Care 1992].
Detection of neuropathyThe role of impaired vibratory perception in the pathogenesis of foot ulceration has been well documented.
[Boulton AJM, et al. Diabet Med 1986]Objective measurement of this sensory parameter with a biothesiometer has been used to identify those at risk at developing ulceration.
[Young MJ et al. Diabet Care 1994]
The Sensitometer An Answer Sensory deficits of vibration perception thresholds is measured as micron displacement of the vibrator tip or as the voltage applied to the tip. These can be read off the control panel
Wide ranging gradations
The meter has two scales as shown in the voltage panel. Lower one is in Microns. This is the actual scale, with a large range of measurement from 0.025 to 25 microns, a ratio of nearly 1:1000.The upper scale is for voltage. It is widely accepted ( 0 to 50 Volts) as it is more convenient. This helps establish wide ranging differentiation of Vibratory Perception Threshold ( VPT )
Sensitometer - Measures accurately the Vibration Perception Threshold, in an upgraded, validated and endorsed instrument.
Sensitometer is a simple to operate, easy to use equipment. The simplicity does not lower the accuracy nor affects reliability.
Hold the probe in hand and apply its button on any these points on both the feet systematically. These are 6 points for testing on the foot
The big toeFirst meta tarsal headThird meta tarsal headFifth meta tarsal headIn stepHeelRecord Voltages
How to use the Sensitometer?Apply the tip to the points one by one as above
Slowly rotate the knob clock wise to increase the voltage / vibration.
How to use the Sensitometer?Record at what level of vibrations, patient respondsSlowly lower the voltage / vibration till the patient says noRaise again to reach the point of first sensation & record
How to use the Sensitometer?
The turn around way:Raise the voltage by 8 quickly, if there is no response raise by 8 till the response is generated Then make a turn around by lowering the voltages
How to use the Sensitometer?
The turn around way:Lower the voltage by installments of 4 till the sensation is lost.Now we have two points of first detection and first loss of sensation.
How to use the Sensitometer?
Now raise the voltages by 2 volts till a response is obtained.Now lower the voltage by 1 till you reach the point of just detectable. This is a faster methodCompare it with reference value,
If you find inconsistent readings Use the silent buttonIts just bellow the power on/off switchOn pressing it the vibrations ceaseBut the meter reading dose not changeOne can thus verify the reliability of the patient response
The Sensitometer Implications of a studyThe Indian normal on field testing appears to be between 8 to 11 volts on feet of non diabetic men and women. There seems to be a rise in the baseline commonly among diabetics, compared to normal in a clinic based study. The deficits detected can be linked to the excess risk of ulceration of a diabetic foot
Prospective Foot Ulcer StudyResults Foot Ulcers VPT25Total ulcers 1988-92 6 2 41Risk per patient 2.9% 3.4% 19.6%Risk/patient/year 0.7% 0.9% 04.9%AJM Boulton
The Sensitometer Implications of a study - 1The risks compared to a normal diabetic foot go up as voltages go beyond 11.25 volts is a critical value - Risk of ulceration rises three to fourfold Above 42 volts it rises to 23 fold
The Sensitometer Implications of a study - 2Repeat Study after 6 months or 1 year is useful. It will tell if - Any intervention for improvement has reduced the voltages required, maintained the same or has increased, indicating that the neural damage has not haltedRethink about what we are doing is a must then