FROM GENES TO BRAIN IMAGING: ADVANCES IN
OUR UNDERSTANDING OF NEUROPATHIC PAIN
David Bennett
Wellcome Clinical Scientist,
Nuffield Department of
Clinical Neurosciences,
University of Oxford
Honorary Consultant neurologist,
Oxford University Hospitals
The definition of neuropathic pain
IASP: ‘Pain arising as a direct
consequence of a lesion or disease
affecting the somatosensory system’
Peripheral neuropathy eg. diabetes, HIV
Post herpetic neuralgia
Trigeminal neuralgia
Multiple sclerosis
Post stroke pain
The problem of neuropathic pain
Bouhassira et al., Pain 2008 performed a postal survey of the general
population (30 000) in France.
20% of respondents had pain described as moderate to severe In 25% of
such cases the pain was defined as neuropathic.
Likely to see increasing prevalence of neuropathic pain with increasing
longevity and the rising incidence of diabetes mellitus.
Neuropathic pain:
• Pathogenesis of neuropathic pain:
Human genetics
Excitability and ion channel dysfunction
Neuro-inflammation
Altered processing within the CNS
• Diagnosis and patient stratification
• The approach to treatment
Neuropathic pain:
• Pathogenesis of neuropathic pain:
Human genetics
Excitability and ion channel dysfunction
Neuro-inflammation
Altered processing within the CNS
• Diagnosis and patient stratification
• The approach to treatment
Nav1.8
Nav1.9
l
l
HCN2
Kv
l
P
response
Bradykinin........BK1/2
Prostanoids.............EP
ATP ..........P2Y
Nav1.7
Nav1.7
l
ATP..............P2X
Temp/H+ .....TRPV1,2
Osmo.........TRPV4
Cold/irrit.........TRPA1
Cool........TRPM8
H+ ..........ASIC
Mechano................?
α2δ1
Sensitisation
stimulus
Cav
Bennett and Woods Lancet Neurology 2014
Case Hx 1: Congenital insensitivity to pain
26 yr old male
Never experienced pain
Over 20 fractures
Multiple injuries to the mouth
Short stature
Anosmic
Normal sensorimotor function
except no perception of pain
Cutaneous innervation maintained
Ramirez
Neurology 2014
Case Hx 1: Sensory testing
Hypersensitive
Hyposensitive
Painless channelopathy: Genetic basis
Cox JJ et al., Nature 2006
Nainherited
v1.7
erythromelalgia:
Nerve conduction studies : Normal
EC
Intra-epidermal nerve fibre density: Normal
Genetic testing: L858F mutation in NaV 1.7 (SCN
IC
NH2
R830X
FS1773
COOH
Case Hx 1: A painless channelopathy
BRN3a/NFAlex Clark
25mv
Case Hx 1: A painless channelopathy
100mS
shoulder
NaV1.7 null
0mV
No AP’s
Control
8
6
4
2
0
0
50pA
Greg Weir
150pA
250pA
200
400
Current (pA)
Case Hx 2: Inherited erythromelalgia
30 year old lady
Red feet at birth.
Feet became increasingly painful.
Erythema and pain worse in warmth relieved by cooling.
Medication: No response to opiates and an array of AEDS
Partial response to topical lidocaine plaster.
Case Hx 2: Inherited erythromelalgia
4
Hyper
Hypo
Z-score
3
2
1
0
-1
-2
-3
-4
-5
inherited erythromelalgia:
Nerve conduction studies : Normal
Navinherited
1.7
erythromelalgia:
Intra-epidermal nerve fibre density: Normal
Nerve conduction studies : Normal
Q875E
EC
Genetic testing: L858F
mutation in NaV 1.7 (SCN 9a)
W1538R
Intra-epidermal nerve fibre density: Normal
S211P
N395K
I136V
Genetic F216S
testing:
L858F
S241T
A863P
IC
Q10R
NH2
V872G
mutation in NaV 1.7 (SCN 9a)
I848TdelL955
L858F
L858H
I234T
S241T
G616R
A1746G
F1449V
P1308L
V1316A
COOH
Erythromelalgia: Mechanism
DRG cell hyperexcitability:
Dib Hajj 2005
Mutations in NaV 1.7 and gain of function
pain phenotypes:
Nav1.7
inherited)
Erythromelalgia
EC
IC
Paroxysmal extreme pain disorder
Fertleman et al., Neuron 2006 52(5) 767
Fertleman et al., 08
Small fibre neuropathy
Faber et al., Ann Neurology 2012 71(1) 26
NH2
COOH
Sensory phenotyping in painful diabetic
neuropathy
PAIN
IN PERIPHERAL
NEUROPATHY
STUDY
Collaborators:
A Rice (Imperial)
S Tesfaye (Sheffield)
Rare variants in Ion channels as risk factors for acquired
neuropathic pain:
Nav1.7
inherited)
EC
IC
COOH
NH2
5
5
0
0
-5
-5
CDT WDT
TSL
CPT
HPT
MDT
VDT
MPT
MPS
WUR PPT
Treatment
• NaV1.7 channelopathies:
Mexiletine, Carbamezipine
Topical lidocaine
Selective NaV1.7 inhibitors-
Cregg et al.,
BJP 2014
Acquired neuropathic pain syndromesAn acquired channelopathy?
et al., ScienceJuly
20002014
Haroutounian, PAIN. Boucher
155(7):1272-1279,
Altered gene expression following nerve injury
Nerve injury
vs Sham
3574
-log (adj.P-val)
3994
Log 4 Fold Change
Altered gene expression following nerve injury
Nerve injury
vs Sham
3574
-log (adj.P-val)
3994
ion channel
expression
Up-regulated:
21 genes
alpha2/delta subunit 1
Piezo-1
P2RX7
P2RX4
167 genes
unchanged
Down-regulated
108 genes
KCNS1
Piezo-2
Log 4 Fold Change
Neuropathic pain:
• Pathogenesis of neuropathic pain:
Human genetics
Excitability and ion channel dysfunction
Neuro-inflammation
Altered processing within the CNS
• The relationship of neuropathic pain to nerve
repair
• Diagnosis and patient stratification
• The approach to treatment
The immune response
Cells
Pro-inflammatory
Cytokines/chemokines
Antibodies
Repair
Neuroinflammation in the PNS
Naive
Injured
Neuroinflammation in the PNS: Dorsal root
ganglion
ASC
IBA1
Naive
ASC
IBA1
Nerve injury
Neuroinflammation in the PNS: Dorsal root ganglion
Naive
Injured
Neuroinflammation: spinal cord changes well described
in rodent
Peripheral nerve injury results in microglial activation
both within the dorsal and ventral horn.
Injured
surveying
effector
IBA1 immunostaining (L5) following spinal nerve ligation
(Calvo et al., J Neurosci 2010).
Neuroinflammation: spinal cord
Astrocyte
Primary afferent
Injury signals
chemokines
Microglia
BDNF
AMPA R NMDA R
GABA R
↓KCC2
T-lymphocyte
Dorsal horn neuron
Glial activation noted in human pain states:
Loggia et al., BRAIN 2015: 138; 604–615
Neuropathic pain:
• Pathogenesis of neuropathic pain:
Human genetics
Excitability and ion channel dysfunction
Neuro-inflammation
Altered processing within the CNS
• The relationship of neuropathic pain to nerve
repair
• Diagnosis and patient stratification
• The approach to treatment
CNS processing and
Neuropathic pain
Altered processing within the CNS: Insights from brain
imaging. Collaboration with A Segerdahl and I Tracey
The effect of cooling on ongoing pain in erythromelalgia
120
Temp oC
Pain (VAS)/temp
100
Pain (VAS)
80
60
40
20
0
1
10
20
30
40
Time (minutes)
50
Altered processing within the CNS: Insights from brain
imaging.
Z=5.0
Z=3.5
Z=2.0
L
R
A :Frontal medial cortex B: Paracingulate
I : Precentral gyrus
J: Postcentral
gyrus
K: ACC
L: MCC
M: PCC
N: Angular gyrus
O :Middle frontal
gyrus
P: PCC
Q : Angular gyrus
R :Superior frontal gyrus
T :Superior frontal gyrus
S: Postcentral gyrus U: Postcentral gyrus
Segerdahl et al., Pain 2012
Altered processing within the CNS: Insights from brain
imaging.
PAIN
IN PERIPHERAL
NEUROPATHY
STUDY
Arterial spin labelling ‘resting state’ diabetic neuropathy
Chronic pain (+) > Chronic pain (-)
L
6.0
z >2.3
z= 4
> FEAT: Mixed Effects, z>2.3, p<0.05 (cluster corrected) n=30
Restings scan (7min)
Age = nuisance regressor
Descending controls
Off-Cell
On-Cell
5HTR 2/3
Opioids
Noradrenaline
5HTR 1/7
West et al., Neuroscience 2015
Neuropathic pain:
• Pathogenesis of neuropathic pain:
Human genetics
Excitability and ion channel dysfunction
Neuro-inflammation
Altered processing within the CNS
• Diagnosis and patient stratification
• The approach to treatment
Diagnosis and patient stratification
A grading system is used depending on the degree of
confirmatory evidence:
Treede et al., in
Neurology 2008
Distribution of pain in diabetic neuropathy
Neuropathic pain
Non-Neuropathic
pain
Diabetic neuropathy
No neuropathic pain
Diabetic neuropathy
Neuropathic pain
Diagnosis and patient stratification:
Sensory symptoms and signs
Diagnosis and patient stratification:
Sensory symptoms and signs
Sensory phenotype: Quantitative sensory testing
Detection thresholds
Pain thresholds
Wind-up, Allodynia
Sensory phenotype: Quantitative sensory testing
DFNS
DMA
Z-Scores
1.5
0.5
-0.5
-1.5
-2.5
-3.5
Right foot
Left foot
PHS
100
3
10
2
x/3
Pain rating (0-100)
CDT WDT TSL CPT HPT PPT MPT MPS WUR MDT VDT
1
1
0
0
QST: Gain or loss of function
PAIN
IN PERIPHERAL
NEUROPATHY
STUDY
G a in o f fu n c t io n
60
P a in le s s N e u ro p a th y
M ild n e u ro p a th ic p a in
40
M o d e ra te /S e v e r e N e u ro p a th ic P a in
##
% p a r tic ip a n ts
20
**
0
-2 0
L o s s o f fu n c tio n
**
-4 0
**
†
**
†
*
-6 0
†
*
*
-8 0
W DT
CDT
TSL
CPT
HP T
MDT
VD T
MPT
MPS
W UR
PPT
DMA
P HS
Neuropathic pain:
• Pathogenesis of neuropathic pain:
Human genetics
Excitability and ion channel dysfunction
Neuro-inflammation
Altered processing within the CNS
• Diagnosis and patient stratification
• The approach to treatment
Better patient stratification can help individualise
treatment:
NNT in different groups defined by sensory
phenotype:
3.9 (95% CI 2.3-12) in the irritable
13 (95% CI 5.3-1) in the non-irritable
nociceptor phenotype
Treatment of neuropathic pain:
First line:
SNRI eg. Duloxetine
TCAs: amitriptyline/nortriptyline
Gabapentinoids: Pregabalin and Gabapentin
Second line: Tramadol
Topical: Lidocaine plaster
High dose capsaicin patch
Third line:
Strong opiates
Botulinum toxin
Future:
More specific sodium channel blockers-
Targeted therapeutics:
Biologic agents:
Small molecules
Goldberg et al Pain
.2012 Jan;153(1):80-5.
Zakrzewska et al. Trials 2013, 14:402
Conclusions:
• Neuropathic pain is associated with profound plasticity at all
levels of the somatosensory nervous system.
• Human genetics has given us new insights into pain
pathophysiology as well as new drug targets.
• We are now much better at stratifying patients and increasingly
are trying too link this to pathophysiological mechanisms.
• Not only are we seeing new treatments but we are learning to
use existing treatments better.
Acknowledgements:
David.bennett@ndcn.ox.ac.uk
My lab:
Oxford
Angela Vincentl
Irene Tracey
Collaborators:
KCL
SB McMahon
Natalie Richards
John Dawes, Alex Clark, Juan Ramirez, Annina
Schmid, Andreas Themistocleous, Greg Weir
UCL
JJ Cox
JN Wood
R Cregg
R Wederhausen
Imperial
A Rice