peripheral nerve field stimulation: mirage or reality?

PERIPHERAL NERVE FIELD STIMULATION: MIRAGE OR REALITY?Dr Paul Verrills Interventional Pain PhysicianMBBS FAFMM MPainMed FIPPMetro Spinal Clinic, Australia

Disclosures

Royalties: NIL Shareholder for Clinical Intelligence Pty Ltd Teaching – Consultant (adhoc peer-peer) Nevro Corporation St. Jude Medical Medtronic Arthrocare Mundipharma Spinal Modulation Boston Scientific

Peripheral Nerve field Stimulation

subcutaneous implantation of percutaneous leads in the

painful areas

electrical field around the activated bipoles

field of paresthesia within the peripheral distribution of pain

Peripheral Nerve field Stimulation

Theory behind Neuromodulation:

stimulation of large myelinated fibres closes the gate (via spinal cord)

putative inhibitory neurotransmitters thought to be released during

large myelinated nerve fibre stimulation include:

gamma-aminobutyric acid (GABA)

adenosine

Peripheral Nerve field Stimulation

Scientific challenges: exact mechanism of producing pain relief is poorly understood

lack of prospective randomized clinical studies

no unifying protocol for implantation

confusion in regards to Indications for the PNfS

lack of scientific data on:

adequate lead depth of implant

adequate parameters for implant

stimulation modalities

Metro Spinal Clinic PNfS lead depth study (2011)

observational study (n = 28) low-back, n = 19 (17 subcutaneous and 2 iliac crest

nerve stimulation)

occipital nerve stimulation, n = 9

influence of (1) electrode depth and (2) electrode

configuration on sensation perception

Metro Spinal Clinic PNfS lead depth study (2011)

1. Abejón D., Deer T., Verrills P. 2011. Subcutaneous Stimulation: How to Assess Optimal Implantation Depth. Neuromodulation 2011; e-pub ahead of print. DOI: 10.1111/j.1525-1403.2011.00357

2. McRoberts WP., Cairns K. 2010. A Retrospective Study Evaluating the Effects of Electrode Depth and Spacing for Peripheral Nerve Field Stimulation in Patients with Back Pain. North American Neuromodulation Society Meeting, Las Vegas. Poster Presentation.

References

Metro Spinal Clinic PNfS lead depth study (2011)

Electrode depths were measured using the 'pin-drop- technique’.

Programming combinations used in the study

Distribution of lead depth in PNfS:ONS vs PNLI

Lead depth Correlates with Perception Threshold

• Pearson Correlation = 0.348, p≤0.001• n= 459 data points from 27 patients (head and low back subcutaneous) with 18

different stimulation configurations (27 points missing)

= data obtained from McRoberts et al.

Similar trends were observed between the two studies.

Lead depth studies

Across three separate studies using three different depth measurement methods, low back subcutaneous paresthesia

was observed at an average lead depth of 9.2 - 10.5mm.

Paresthesia Descriptions

Paresthesia descriptions were classified into 5 groups based on cutaneous fibre type

Distribution of categorised sensations at maximum discomfort

Distribution of categorised sensations at 70% usage range

Distributions of sensations at maximum discomfort amplitude

• The LBP and ONS groups have similar distributions. Major sensations experienced are tingling, vibration, pinch, and stabbing.

Low back PNfS has higher perception thresholds than ONS

Head (ONS) n = 8

Low Back n = 13

Study summary

1. Implant depth of 10~12 mm from the surface can maximise the

target sensation (Aβ_FA) of PNfS effective pain relief.

2. Cathodal threshold is lower than anodal one (as in Spinal cord

Stimulation (SCS)).

However, it is likely that anodes reach threshold within the normal usage range of

current in PNfS.

3. In PNFS both cathodes and anodes may be used to target the

stimulation location.

=

PNfS 200 cases study

IRB approved

Prospective observational study over 2 years +

203 patients with intractable pain

Key pain regions: Occipital / craniofacial

Thoracic

Abdominal / groin

Low back

PNfS 200 cases

Outcomes: Average pain (11 - point NPRS / VAS scale)

Percentage pain relief (%)

Oswestry Disability Index (ODI)

Analgesic medication use

Changes to paid employment (if applicable)

Patient satisfaction with the treatment

Adverse events monitored

Results: occipital - craniofacial

• n = 63• an average pain reduction of 4.9 ± 0.32, on an 11-point scale

was reported (***p≤0.0001, Wilcoxon Mann-Whitney U-test)

Pre PNfS Post PNfS0

2

4

6

8

10

7.4

2.7

Reduction in Pain(data shown as Average Pain ± SEM)

11 –

poi

nt P

ain

Scal

e ***

Results: thoracic

• n = 17• an average pain reduction of 5.3 ± 0.56, on an 11-point scale

was reported (***p≤0.0001, Wilcoxon Mann-Whitney U-test)

Pre PNfS Post PNfS0

2

4

6

8

10

7.3

2.3

Reduction in Pain(data shown as Average Pain ± SEM)

11 –

poi

nt P

ain

Scal

e

***

Results: abdominal / groin

• n = 15• an average pain reduction of 5.8 ± 0.52, on an 11-point scale

was reported (***p≤0.0001, Wilcoxon Mann-Whitney U-test)

Pre PNfS Post PNfS0

2

4

6

8

10

7.3

1.6

Reduction in Pain(data shown as Average Pain ± SEM)

11 –

poi

nt P

ain

Scal

e

***

Results: low back

• n = 108• an average pain reduction of 4.1 ± 0.26, on an 11-point scale

was reported (***p≤0.0001, Wilcoxon Mann-Whitney U-test)

Pre PNfS Post PNfS0

2

4

6

8

10

7.2

3.4

Reduction in Pain(data shown as Average Pain ± SEM)

11 –

poi

nt P

ain

Scal

e

***

Results: occipital / craniofacial

• 66% of patients reported good (>50%) to excellent (>75%) pain relief

Excellent (100-75%)

Good (75-50%) Fair (49-25%) Poor (<24%) No Change0

10

20

30

40

50

60

70

42%

23.8%12.7% 7.9% 1.6%

% Pain Relief Experienced by Patients with PNfS(n = 63)

Prop

ortio

n of

Pat

ient

s (%

)

Results: thoracic

• 82% of patients reported good (>50%) to excellent (>75%) pain relief

Excellent (100-75%)

Good (75-50%) Fair (49-25%) Poor (<24%) No Change0

10

20

30

40

50

60

70

58.8%

23.5%11.8%

0%

5.9%

% Pain Relief Experienced by Patients with PNfS(n = 17)

Prop

ortio

n of

Pat

ient

s (%

)

Results: abdominal / groin

• 87% of patients reported good (>50%) to excellent (>75%) pain relief

Excellent (100-75%)

Good (75-50%) Fair (49-25%) Poor (<24%) No Change0

10

20

30

40

50

60

70

66.7%

20% 13.3%0% 0%

% Pain Relief Experienced by Patients with PNfS(n = 15)

Prop

ortio

n of

Pat

ient

s (%

)

Results: low back

• 68% of patients reported good (>50%) to excellent (>75%) pain relief

Excellent (100-75%)

Good (75-50%) Fair (49-25%) Poor (<24%) No Change0

10

20

30

40

50

60

70

35.2% 32.4%15.8% 5.5% 11.1%

% Pain Relief Experienced by Patients with PNfS(n = 108)

Prop

ortio

n of

Pat

ient

s (%

)

Results: combined areas

• combined regions PNfS, n = 203• an average pain reduction of 4.3 ± 2.5, on an 11-point scale was

reported (**p≤0.00, Wilcoxon Mann-Whitney U-test)

Pre PNfS Post PNfS0

2

4

6

8

10

7.3

3.0

Reduction in Pain(data shown as Average Pain ± SEM)

11 –

poi

nt P

ain

Scal

e **

Results: combined areas

• 73% of patients reported good (>50%) to excellent (>75%) pain relief

Excellent (100-75%)

Good (75-50%) Fair (49-25%) Poor (<24%) No Change0

10

20

30

40

50

60

70

42%31%

14% 5%8%

% Pain Relief Experienced by Patients with PNfS(combined regions, n = 203)

Prop

ortio

n of

Pat

ient

s (%

)

Does the pain relief last post-implant?

Sustained pain relief: combined areas

• Pain relief achieved shortly after implantation was sustained for greater than 12 months

≤ 12 months follow up ≥ 12 months follow up ≥ 24 months follow up0

2

4

6

8

10

Pre,7.3

Post, 2.9

Pain Relief post-implant

VAS

Pain

Sco

res

n = 203

Sustained pain relief: combined areas

• Pain relief achieved shortly after implantation was sustained for greater than 12 months

≤ 12 months follow up ≥ 12 months follow up ≥ 24 months follow up0

2

4

6

8

10

Pre,7.3 Pre, 7.4

Post, 2.9 Post, 3.0

Pain Relief post-implant

VAS

Pain

Sco

res

n = 203 n = 203

Sustained pain relief: combined areas

• Pain relief achieved shortly after implantation was sustained for greater than 12 months

≤ 12 months follow up ≥ 12 months follow up ≥ 24 months follow up0

2

4

6

8

10

Pre,7.3 Pre, 7.4 Pre, 7.3

Post, 2.9 Post, 3.0Post, 3.8

Pain Relief post-implant

VAS

Pain

Sco

res

n = 203 n = 203

n = 68

Results: combined areas

Extreme Decrease

Moderate Decrease

Slight Decrease

Increase No Change Unsure0

10

20

30

40

50

40%

26%

8% 4%20%

2%

Changes to Analgesic Usefollowing neuromodulation (combined regions, n = 203)

Prop

ortio

n of

Pat

ient

s (%

)

• 74% of patients reduced their analgesic use• reduction in analgesics correlated with improved pain relief (next slide)

Results: combined areasPain Relief correlates with Decreased Analgesic Use

Good

Fair

PoorPain

Rel

ief

N/A NoChange

Increased Slightdecrease

ModerateDecrease

ExtremeDecrease

Change in Analgesic Use

Excellent

Pearson’s Correlation, r = 0.704; p ≤ 0.0001

Results: combined areas

• Pre PNfS = 34.4 13.5 vs ≥ 12 months Follow Up = 28.3 6.4 (n = 203) • Disability was reduced following PNFS; (*p ≤ 0.03, t-test )

*

Results: combined areas

0

10

20

30

40

50

12%

40%

0%8%

16%24%

Changes to paid employment following PNFS for pa-tients below 60 years (≥ 12 months)

Prop

ortio

n of

Pat

ient

s (%

)

48%

• 48% of patients below the age of 60 years increased their capacity for paid employment.

Complications and adverse eventsOUTCOMES

Complication No. of patients

Reposition / Re-implant / Replace Explant

2007 2008 2009 2010 2011 2007 2008 2009 2010 2011

Hardware erosion 10 1 3 1 1 1 1 1 1

Lead Infection 2 1 1

Leads too superficial 5 1 2 1 1

Hardware migration 5 1 1 2 1

IPG pain 2 1 1

Implant rejection 2 1 1

TOTAL COMPLICATIONS2007 2008 2009 2010 2011

3 6 5 7 5

26 patients total(12.8% of all cases)

Patient satisfaction (≥ 12 months)

Completely Sat-isfied

Very Satisfied Satisfied Not Comletely Satisfied

Unsatisfied0

10

20

30

40

50

60

70

28%35%

22%

6% 8%

Prop

ortio

n of

Pat

ient

s, %

• Overall, 85% of patients were satisfied with their outcome

Summary

Science behind PNfS

Underlying Issues of PNfS therapy

Clinical data for key pain areas

Combined clinical data for 203 PNfS patients

Conclusions

PNFS therapy for intractable chronic pain

conditions:

Safe

Effective

PNFS has the potential to fundamentally change

the way we think about pain management

Conclusions

Peripheral Nerve field Stimulation

MIRAGE OR REALITY ?