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Neuropathic Pain
Invasive Neurostimulation in the Management
of Chronic Neuropathic Pain Syndromes
a report by
Brian A Simpson
Consultant Neurosurgeon, University Hospital of Wales
Historical Perspective coagulopathy, sepsis and, to a variable extent, cognitive impairment.
The analgesic effect of electricity has been exploited for thousands of
years (electric fish, static electricity) but it has been controllable only since Spinal Cord Stimulation
the introduction of the Leyden jar in 1745. Electro-acupuncture was
introduced in 1823. Peripheral nerve stimulation was also developed in General Comments
the 19th century, but its misuse (‘the golden age of medical electricity’) This is the most widely and commonly used form of internal
led to its ban in the US in 1910. The modern era of therapeutic neurostimulation. The epidural electrodes are placed ipsilateral to the
neurostimulation was launched by the gate control theory of pain pain, because it is necessary to activate the collaterals of the large Aß
transmission,
1
although deep brain stimulation (DBS) had already been afferents that ascend in the posterior columns of the spinal cord. The
used for pain control.
2
It was also driven by the dawning awareness that rostro-caudal and lateral positioning of the electrode system must be
damage to the nervous system, including therapeutic damage, could appropriate so that the gentle evoked paraesthesiae cover the painful
itself generate pain – neuropathic pain. The first human application of area. Originally, monopolar systems were used, then bipolar and now
spinal cord stimulation (SCS) was in 1967.
3
16 contacts are commonly available, requiring computer assistance for
General Considerations
Physical treatments such as electrical neurostimulation have clear
advantages over pharmacotherapy in terms of adverse side effects.
Physical treatments such as electrical
Despite this and the fact that fewer than half of patients with chronic
neurostimulation have clear advantages
neuropathic pain obtain worthwhile long-term pain relief from drugs,
4
implanted neurostimulators are regarded as a treatment of last resort.
over pharmacotherapy in terms of
This is only partly due to the high initial cost involved; cost-effectiveness
adverse side effects.
studies are consistently positive, with a crossover point in less than three
years
5
(probably a little later, but with greater long-term benefit, in the
case of the more expensive recently introduced rechargeable systems).
programming. Dual-channel and multichannel programming permit
The biggest hurdle facing the field is the issue of evidence. There is a electronic steering of the stimulation topography, greatly reducing the
large body of positive but uncontrolled published evidence and enormous need for physical repositioning of the electrodes. Electrodes are either
unpublished positive experience, but very little ‘level one’ evidence. Not of the wire/catheter type, which can be inserted percutaneously via a
only does this provide the financially constrained healthcare Tuohy needle under local anaesthesia or in the form of a paddle, which
commissioners and insurers with an excuse, but it is also relevant to the requires an open operation. The former are less invasive but are
key factor of case selection. electrically inefficient and more prone to dislodgement than ‘surgical’
systems. The latter perform better but require both a surgeon and a
There are remarkably few contraindications: the presence of an implanted bigger procedure for insertion. The power comes from an implanted
cardiac defibrillator or a demand-type cardiac pacemaker, uncontrolled pulse generator similar to a cardiac pacemaker and the electronic
parameters are programmed by telemetry. External power sources
coupled to an implanted receiver–transducer by radiofrequency are
Brian A Simpson is a Consultant Neurosurgeon at the
available for cases in which power demand is high, but the recent
University Hospital of Wales, Cardiff, where he has
developed an active practice in functional neurosurgery,
introduction of rechargeable implantable systems avoids the need for
particularly the surgical treatment of pain, including
frequent replacements in a more elegant way.
neurostimulation. His research into the role of dopamine
systems in sensorimotor integration led to an MD degree
from Cambridge University. He has lectured and published Indications
widely on the subject and has contributed to the
In broad terms, SCS is effective for neuropathic and ischaemic pain and
development of the International Neuromodulation Society,
serving as President from 2000 to 2003. He was educated
does not influence nociceptive pain (e.g. arthritis, acute wound pain,
at Trinity Hall Cambridge and the London Hospital Medical etc.).
6
The most common applications, which have also provided the best
College, qualifying in 1973 and becoming FRCS in 1978.
evidence for efficacy, are complex regional pain syndrome (CRPS) and the
E: brian.simpson@cardiffandvale.wales.nhs.uk
poorly named failed back surgery syndrome (FBSS). FBSS, i.e. pain in the
leg and/or back persisting after one or more lumbar spine operations, is
34 © TOUCH BRIEFINGS 2007