vpt assessment in neuropathy

1. 1
Quantitative tests forQuantitative tests for
neuropathic assessment - 1neuropathic assessment - 1
Quantitative sensory testing (QST) is theQuantitative sensory testing (QST) is the
determination of the absolute sensorydetermination of the absolute sensory
threshold, defined as the minimal energythreshold, defined as the minimal energy
required to reliably stimulate the particularrequired to reliably stimulate the particular
modality of sensation to be detected.modality of sensation to be detected.

2. 2
Quantitative tests forQuantitative tests for
neuropathic assessment - 2neuropathic assessment - 2
The higher the level of the minimal energyThe higher the level of the minimal energy
required the greater is the deficit of functionrequired the greater is the deficit of function
of the particular modality of sensation.of the particular modality of sensation.

3. 3
Quantitative tests forQuantitative tests for
neuropathic assessment - 3neuropathic assessment - 3
In vibration threshold measurement the energy isIn vibration threshold measurement the energy is
delivered as voltage converted in the vibration ofdelivered as voltage converted in the vibration of
the probe. On VPT sensitometer, both voltage andthe probe. On VPT sensitometer, both voltage and
vibration ie spatial disfigurement to and fro of thevibration ie spatial disfigurement to and fro of the
skin can be measured.skin can be measured.

4. 4
Quantitative tests forQuantitative tests for
neuropathic assessment - 4neuropathic assessment - 4
The higher the deficit of function theThe higher the deficit of function the
greater voltage is required, ie greatergreater voltage is required, ie greater
displacement for the limb to sense vibration.displacement for the limb to sense vibration.

5. 5
Quantitative tests forQuantitative tests for
neuropathic assessment - 5neuropathic assessment - 5
The higher the deficit of function theThe higher the deficit of function the
greater voltage is required, ie greatergreater voltage is required, ie greater
displacement for the limb to sensedisplacement for the limb to sense
vibration.vibration.
Has great implications in prognosis andHas great implications in prognosis and
therapy.therapy.

6. 6
Quantitative tests forQuantitative tests for
neuropathic assessment - 6neuropathic assessment - 6
QST is a relatively simple procedure that is bothQST is a relatively simple procedure that is both
noninvasive and nonabrasive.noninvasive and nonabrasive.
In assessing diabetic neuropathy, the paramountIn assessing diabetic neuropathy, the paramount
concern is to detect the integrity of the axonsconcern is to detect the integrity of the axons
forming the peripheral nervous system and theirforming the peripheral nervous system and their
distal receptors.distal receptors.

7. 7
Quantitative tests forQuantitative tests for
neuropathic assessment - 7neuropathic assessment - 7
Measurable Modalities:Measurable Modalities: Vibration ThresholdsVibration Thresholds
This measure is the most widely studied QSTThis measure is the most widely studied QST
procedure. It principally assesses functionprocedure. It principally assesses function
in Meissner and Pacinian corpuscles andin Meissner and Pacinian corpuscles and
their associated large-diameter fibers.their associated large-diameter fibers.

8. 8
Quantitative tests forQuantitative tests for
neuropathic assessment - 8neuropathic assessment - 8
Vibration PerceptionVibration Perception
Threshold is the indirectly madeThreshold is the indirectly made
detection of loss of protective paindetection of loss of protective pain
sensation that would render a patientsensation that would render a patient
susceptible to foot ulceration.susceptible to foot ulceration.

9. 9
Other Measurable ModalitiesOther Measurable Modalities
Light Touch:Light Touch:
This measure tests the integrity of Merkel touchThis measure tests the integrity of Merkel touch
domes and Meissner corpuscles and theirdomes and Meissner corpuscles and their
associated large-diameter fibers.associated large-diameter fibers.
Thermal Sensitivity:Thermal Sensitivity:
Known - Marstock ThermodeKnown - Marstock Thermode
The new system: Heat and Cold PerceptionThe new system: Heat and Cold Perception
ThresholdThreshold

10. 10
What do we have for AssessingWhat do we have for Assessing
NeuropathyNeuropathy
Need to
assess associated risk
of ulceration in
a neuropathic
Need to distinguish
Neuropathic and non
neuropathic patients
Need to establish
wide range of quantitated
gradation of sensory deficits
for comparison on
Follow up
Simple test
equipments

11. 11
Have it nowHave it now

12. 12
• The ability to identify feet at risk of ulceration hasThe ability to identify feet at risk of ulceration has
been demonstrated prospectively in two studiesbeen demonstrated prospectively in two studies
using the biothesiometer.using the biothesiometer.
[Young MJ, et al. Diabet Care 1994][Young MJ, et al. Diabet Care 1994]
[Abbott CA, et al. Diabet Care 1998].[Abbott CA, et al. Diabet Care 1998].
• In one study using the monofilament.In one study using the monofilament.
[Rith-Najarian SJ, Diabet Care 1992].[Rith-Najarian SJ, Diabet Care 1992].

13. 13
Detection of neuropathyDetection of neuropathy
• The role of impaired vibratory perception in theThe role of impaired vibratory perception in the
pathogenesis of foot ulceration has been wellpathogenesis of foot ulceration has been well
documented.documented.
[Boulton AJM, et al. Diabet Med 1986][Boulton AJM, et al. Diabet Med 1986]
• Objective measurement of this sensory parameterObjective measurement of this sensory parameter
with a biothesiometer has been used to identifywith a biothesiometer has been used to identify
those at risk at developing ulceration.those at risk at developing ulceration.
[Young MJ et al. Diabet Care 1994][Young MJ et al. Diabet Care 1994]

14. 14
The SensitometerThe Sensitometer
An AnswerAn Answer
• Sensory deficits of vibration perceptionSensory deficits of vibration perception
thresholds is measured as micronthresholds is measured as micron
displacement of the vibrator tip or as thedisplacement of the vibrator tip or as the
voltage applied to the tip.voltage applied to the tip.
• These can be read off the control panelThese can be read off the control panel

15. 15
Wide ranging gradationsWide ranging gradations
• The meter has two scales as shown in the voltageThe meter has two scales as shown in the voltage
panel. Lower one is in Microns. This is the actualpanel. Lower one is in Microns. This is the actual
scale, with a large range of measurement fromscale, with a large range of measurement from
“0.025 to 25 microns,” a ratio of nearly 1:1000.“0.025 to 25 microns,” a ratio of nearly 1:1000.
• The upper scale is for voltage. It is widely acceptedThe upper scale is for voltage. It is widely accepted
( 0 to 50 Volts) as it is more convenient.( 0 to 50 Volts) as it is more convenient.
• This helps establish wide ranging differentiation ofThis helps establish wide ranging differentiation of
Vibratory Perception Threshold ( VPT )Vibratory Perception Threshold ( VPT )

16. 16
Sensitometer - MSensitometer - Measures accurately theeasures accurately the
Vibration Perception Threshold, in anVibration Perception Threshold, in an
upgraded, validated and endorsedupgraded, validated and endorsed
instrument.instrument.

17. 17
SensitometerSensitometer is a simple to operate,is a simple to operate,
easy to use equipment. The simplicityeasy to use equipment. The simplicity
does not lower the accuracy nor affectsdoes not lower the accuracy nor affects
reliability.reliability.

18. 18
Hold the probe in hand and apply it’sHold the probe in hand and apply it’s
button on any these points on both thebutton on any these points on both the
feet systematically.feet systematically.
• These are 6 points for testing on the footThese are 6 points for testing on the foot
1.1. The big toeThe big toe
2.2. First meta tarsal headFirst meta tarsal head
3.3. Third meta tarsal headThird meta tarsal head
4.4. Fifth meta tarsal headFifth meta tarsal head
5.5. In stepIn step
6.6. HeelHeel
Record VoltagesRecord Voltages

19. 19
How to use the Sensitometer?How to use the Sensitometer?
• Apply the tip to theApply the tip to the
points one by one aspoints one by one as
aboveabove
• Slowly rotate the knobSlowly rotate the knob
clock wise to increaseclock wise to increase
the voltage /the voltage /
vibration.vibration.

20. 20
How to use the Sensitometer?How to use the Sensitometer?
• Record at what levelRecord at what level
of vibrations, patientof vibrations, patient
respondsresponds
• Slowly lower theSlowly lower the
voltage / vibration tillvoltage / vibration till
the patient says nothe patient says no
• Raise again to reachRaise again to reach
the point of firstthe point of first
sensation & recordsensation & record

21. 21
How to use the Sensitometer?How to use the Sensitometer?
• The turn around way:The turn around way:
• Raise the voltage byRaise the voltage by
8 quickly, if there is8 quickly, if there is
no response raise byno response raise by
8 till the response is8 till the response is
generatedgenerated
• Then make a turnThen make a turn
around by loweringaround by lowering
the voltagesthe voltages

22. 22
How to use the Sensitometer?How to use the Sensitometer?
• The turn around way:The turn around way:
• Lower the voltage byLower the voltage by
installments of 4 tillinstallments of 4 till
the sensation is lost.the sensation is lost.
• Now we have twoNow we have two
points of firstpoints of first
detection and firstdetection and first
loss of sensation.loss of sensation.

23. 23
How to use the Sensitometer?How to use the Sensitometer?
• Now raise theNow raise the
voltages by 2 volts tillvoltages by 2 volts till
a response isa response is
obtained.obtained.
• Now lower the voltageNow lower the voltage
by 1 till you reach theby 1 till you reach the
point of justpoint of just
detectable.detectable.
• This is a fasterThis is a faster
methodmethod
• Compare it withCompare it with
reference value,reference value,

24. 24
If you find inconsistent readingsIf you find inconsistent readings
• Use the silent buttonUse the silent button
• It’s just bellow theIt’s just bellow the
power on/off switchpower on/off switch
• On pressing it theOn pressing it the
vibrations ceasevibrations cease
• But the meter readingBut the meter reading
dose not changedose not change
• One can thus verifyOne can thus verify
the reliability of thethe reliability of the
patient responsepatient response

25. 25
The SensitometerThe Sensitometer
Implications of a studyImplications of a study
• The Indian normal on field testing appears to beThe Indian normal on field testing appears to be
between 8 to 11 volts on feet of non diabeticbetween 8 to 11 volts on feet of non diabetic
men and women.men and women.
• There seems to be a rise in the baselineThere seems to be a rise in the baseline
commonly among diabetics, compared to normalcommonly among diabetics, compared to normal
in a clinic based study.in a clinic based study.
• The deficits detected can be linked to the excessThe deficits detected can be linked to the excess
risk of ulceration of a diabetic footrisk of ulceration of a diabetic foot

26. 26
Prospective Foot Ulcer StudyProspective Foot Ulcer Study
Results — Foot UlcersResults — Foot Ulcers
VPT<15 VPT 16-24 VPT>25VPT<15 VPT 16-24 VPT>25
Total ulcers 1988-92Total ulcers 1988-92 66 2 412 41
Risk per patientRisk per patient 2.9% 3.4% 19.6%2.9% 3.4% 19.6%
Risk/patient/yearRisk/patient/year 0.7%0.7% 0.9% 04.9%0.9% 04.9%
AJM BoultonAJM Boulton

27. 27
The SensitometerThe Sensitometer
Implications of a study - 1Implications of a study - 1
• The risks compared to a normal diabeticThe risks compared to a normal diabetic
foot go up as voltages go beyond 11.foot go up as voltages go beyond 11.
• 25 volts is a critical value - Risk of25 volts is a critical value - Risk of
ulceration rises three to fourfoldulceration rises three to fourfold
• Above 42 volts – it rises to 23 foldAbove 42 volts – it rises to 23 fold

28. 28
The SensitometerThe Sensitometer
Implications of a study - 2Implications of a study - 2
• Repeat Study after 6 months or 1 year is useful.Repeat Study after 6 months or 1 year is useful.
It will tell if -It will tell if -
• Any intervention for improvement has reducedAny intervention for improvement has reduced
the voltages required, maintained the same orthe voltages required, maintained the same or
has increased, indicating that the neural damagehas increased, indicating that the neural damage
has not haltedhas not halted
• Rethink about what we are doing is a must thenRethink about what we are doing is a must then