Chapter 61 Spinal Cord Stimulation

Question 1

Spinal cord stimulation (SCS) describes

Answer 1

the use of pulsed electrical energy near the spinal cord to control pain

Question 2

• Spinal cord stimulation (SCS) has notable analgesic properties for

Answer 2

neuropathic pain states, anginal pain, and peripheral ischemic pain. SCS is effective for treatment of Failed Back Surgery Syndrome, complex regional pain syndrome (CRPS),

Question 3

Melzack and Wall proposed the gate control theory proposed

Answer 3

that non-painful stimulation of large myelinated Ab fibers could impede painful stimuli carried by C-fibers and lightly myelinated Ad fibers.

Question 4

Proposed neurophysiologic

mechanisms of SCS

Answer 4

points to SCS having a beneficial effect at the dorsal horn level by favorably altering the local neurochemistry in that zone thereby suppressing the hyperexcitability of the wide dynamic range interneurons. there is some
evidence for increased levels of gamma-aminobutyric acid (GABA) and serotonin, and perhaps suppression of levels of some excitatory amino acids including glutamate and aspartate. In the case of ischemic pain, analgesia seems to be obtained through restoration of a favorable oxygen supply
and demand balance—perhaps through a favorable alteration of sympathetic tone.

Question 5

Electrodes are of two types:

Answer 5

percutaneous versus paddle

Question 6

Electrodes of SCS: paddle leads

Answer 6

flat and wide with insulation on one side and electrical pads on the other. This
has the advantage of directing the current in one direction. Paddle leads must be placed via laminotomy or laminectomy.

Question 7

Electrodes of SCS: Paddle leads

Answer 7

must be placed via laminotomy or laminectomy. Percutaneous leads are cylindrical catheters placed via a needle. Contacts are cylindrical and generate a
less eficient electric field circumferentially around the catheter.

Question 8

Electrodes are connected to

Answer 8

an implanted pulse generator (IPG) or an RF unit

Question 9

The power source options are of three types

Answer 9

primary cell, rechargeable, and RF.

Question 10

Primary cells

Answer 10

tend to be larger and have a short life span of 4 years, but have low maintenance because they do not require charging

Question 11

Rechargeable Implantable Pulse Generator (IPG) system

Answer 11

contain Li-ion cells with a life span of 9 years.

Question 12

Radio Frequency (RF) units

Answer 12

not limited by battery life but require an external power source, which is inconvenient and may result in skin irritation.

Question 13

A stimulator trial

Answer 13

conducted under fluoroscopy with sterile conditions. A lead is introduced into the epidural space with the standard epidural needle placement. The lead is steered under fluoroscopic imaging into the posterior paramedian epidural space up to the desired anatomic location. The needle is withdrawn, an anchoring suture placed into the skin, and a sterile dressing is applied

Question 14

A stimulator trial sedation

Answer 14

Sedation is kept light, and copious local anesthetic is used so that the patient can be awakened after lead placement for evaluatoin of parasthesia coverage over the area of pain.

Question 15

When the patient returns for implant

Answer 15

a new lead is placed in the location of the trial lead and connected to an implanted IPG

Question 16

Alternatively, trial leads can also be implanted with tunneled extensions exiting the skin

Answer 16

during permanent implantation, only the extensions are discarded and the original trial leads can be used to connect to the generator. This method has the advantage of retaining the same lead position in a successful trial, but on the other hand, it adds an incision that increases postoperative pain confounding trial interpretation. Furthermore, implanted leads may have a greater risk for infection than the straight percutaneous method.

Question 17

A careful trial period of

Answer 17

5 to 7 days is advocated to decrease
the risk of a failed implant. Patients are encouraged to pursue normal activities with the exception of aggressive bending or twisting to prevent lead migration.

Question 18

Indicative of a successful trial

Answer 18

Most consider 50% or more pain relief to be indicative of a successful trial, although the ultimate decision also should include other factors such as activity level and medication intake.

Question 19

The technical challenges of permanent lead placement depend on

Answer 19

(1) proper fixation (2) lead redundancy

Question 20

Consistent and reliable stimulation depends on

Answer 20

fixing an electric field over a small area of the spinal cord.

Question 21

Major factor in successful lead placement

Answer 21

sclerotic changes in the tissue surrounding the implanted system stabilizes the leads over the long-run, during the acute phase, proper anchoring is a major factor

Question 22

In the event of minor lead migration

Answer 22

electrode redundancy is used to accommodate for minor shifts by using alternative leads to accommodate the desired electric field.

Question 23

The generator unit is generally implanted in the

Answer 23

lower abdominal area or in the posterior superior gluteal area

Question 24

For cervical or occipital leads, generators are often placed in

Answer 24

between the scapula

Question 25

Generally, generators should be in a location the patient

Answer 25

can access with his or her dominant hand for adjustment of settings or charging

Question 26

Appropriate patients for neurostimulation implant must meet the following criterion

Answer 26

the patient has a diagnosis amenable to this therapy (i.e., neuropathic pain syndromes), the patient has failed conservative therapy, significant psychological issues have been ruled out, and a trial has demonstrated pain relief.

Question 27

The primary endpoint of SCS placement for patients

Answer 27

reinforce to the patient that improvement in pain is not the primary endpoint, but rather it is return to functional activity.

Question 28

Complications with SCS

Answer 28

infections, lack of appropriate paresthesia coverage, to devastating complications, such as paralysis, nerve injury, and death. lead migration or breakage. The generator can also be a source of revision if changes
in body habitus affect the source position. Overall complication rates from spinal cord stimulation range from 28% to 42%. Studies have demonstrated superficial infectious rates ranging from 2.5% to 7.5%,

Question 29

To avoid infectious complications, the

patient should be instructed on

Answer 29

wound care and recognition of signs and symptoms indicative of infection. Many
superficial infections can be treated with oral antibiotics, but more serious infection may require surgical exploration and removal of the device. Although less common, abscess of the epidural space can lead to paralysis and death if not identified quickly, so a high index of suspicion is warranted.

Question 30

Predominant pathogen for percutaneous epidural catheters

Answer 30

Staphylococcus aureus. While there is no standard to avoid infection, prophylactic intraoperative antibiotics are often used, as well as oral antibiotics for 3 to 5 days postoperatively.

Question 31

Four basic parameters in neurostimulation which may be adjusted to create stimulation paresthesias in the painful areas thereby mitigating the patient’s pain

Answer 31

Amplitude, Pulse Width, Rate, and Electrode Selection (PEAR)

Question 32

Amplitude

Answer 32

the intensity or strength of each individual pulse and can be controlled by voltage (V) or current (ohms). There is no evidence of superiority for voltage or current control, however, theoretically, current-control
systems are more immune to changes in electrical resistance in the tissue due to sclerosis and patient positional changes.

Question 33

Amplitudes initial settings

Answer 33

Amplitudes are variable even for an individual patient, but typical initial settings are 60% to 90% of motor threshold.

Question 34

Pulse width

Answer 34

the duration of a pulse measured in microseconds (msec). It is usually set between 100 and 400 msec. A larger pulse width delivers more energy per pulse and typically broader coverage. Common initial settings are 0.2 msec.

Question 35

Rate

Answer 35

measured in hertz (Hz) or cycles per second, between 20 and 120 Hz. At lower rates, the patient may feel myoclonic vibrations, whereas at higher frequencies, the feeling is more of a buzzing sensation. Very high frequencies (>500 Hz) are suggested to increase blood flow
and decrease vascular resistance.

Question 36

Programming modes that save battery life include

Answer 36

Cycling mode during which the stimulator cycles full on/off at patient determined intervals (minutes, seconds, or hours).

Question 37

Peripheral nerve stimulation

Answer 37

Shown efficacy for peripheral nerve injury pain syndromes as well as CRPS, with the use of a carefully implanted paddle lead using a fascial graft to help anchor the lead without traumatizing the nerve.

Question 38

Motor cortex and deep brain stimulation

Answer 38

techniques that have been explored to treat highly refractory neuropathic pain syndromes including central pain, deafferentation
syndromes, trigeminal neuralgia, and others. Deep brain stimulation has become a widely
used technique for movement disorders, and much less so for painful indications

Question 39

Current stimulators are contraindicated for use within

Answer 39

magnetic resonance imaging (MRI) due to the risk of magnetically generated currents heating the leads and causing neural injury

Question 40

Stimulation should be applied with

Answer 40

low intensity, just suprathreshold for the
activation of the low-threshold, large-diameter fibers, and should be of nonpainful intensity. To be effective SCS must be applied continuously (or in cycles) for at least 20 min prior to the onset of analgesia. This analgesia develops slowly and typically lasts several hours after cessation of the stimulation

Question 41

Insulated, paddle-type electrodes probably

decrease the incidence of

Answer 41

lead breakage, prolong battery life, and show
early superiority in quality of paresthesia coverage and analgesia in FBSS as compared to permanent percutaneous electrodes.