W8 Spinal Cord Stimulation Flashcards
Treatment of Neuropathic Pain Re. Saluda Medical
For the following types of nerve fibres, list for each the
i) Information Carried,
ii) whether the fibre has a Myelin Sheath (or not),
iii) the Diametre of the fibre (micrometers) and
iv) the Conduction Speed (m/s).
- A-alpha
- A-beta
- A-delta
- C
A-alpha
- proprioception, myelinated, 13-20 um, 80-120 m/s
A-beta
- touch, myelinated, 6-12 um, 35-90 m/s
A-delta
- pain (mechanical and thermal), myelinated, 1-5 um, 5-40 m/s
C
- pain (mechanical, thermal and chemical), non-myelinated, 0.2-1.5 um, 0.5-2 m/s
Define:
- Hyperalgesia
- Allodynia
Hyperalgesia: an increased sensitivity to pain which may be caused by nociceptors or peripheral nerves
Allodynia: the triggering of a pain response from stimuli which do not normally provoke pain
(see image)
Describe First, Second and Third-line therapies for Neuropathic Pain following Diagnosis (treatment order)
First-Line Therapies:
- Cognitive and Behavioural Modifications
- Non-Steroidal Anti-Inflammatory Drugs (NSAIDs)
- Transcutaneous Electrical Nerve Stimulation (TENS)
- Biofeedback
- OTC Pain Medications / Rehabilitative Therapy
Second-Line Therapies:
- Systemic Opioids
- Nerve Blocks
Third-Line Therapies:
- Neurostimulation
- Implantable Drug Pumps
- Neuroablation
Where was the first spinal cord stimulator prototype implanted and when?
- J Mortimer and N Shealy began work on SC Stimulator Prototype in ‘66
- In ‘67, first implanted device with Subarachnoid Electrode Placement
List the competing existing Spinal Cord Stimulation systems in market and future new SCS systems in development.
Existing SCS Systems:
- Boston Scientific - Multiple Current Sources; Biphasic charge-balanced stimuli
- St Jude Medical - Single Current Source; Monophasic current source passive charge recovery
- Medtronic
New:
- Spinal Modulation - Dorsal Root Ganglion Target; Address movement, stable location
- Nevro - Paraesthesia Free
Describe the Spinal Cord Stimulator Market and the main Issues faced by companies such as Saluda Medical.
- ~2b annually in sales
- No real product innovation for 25 years
- Therapies are based on empirical clinical expeirments, not basic science –> the effects of stimulation need to be measured
Issues:
-
Unpredictable Benefit
- trial stimulation is needed to assess benefit
-
Unstable Therapy
- patient movement produces over-stimulation
- long-term electrode migration
-
Invasive Process
- long procedure time
- paraesthesia and side effects
Anecdotally SCS is said to work for 65% of people who achieve 50% or better pain relief.
The Saluda Medical SCS device measures the response of nerves to stimulation, an ECAP (Evoked Compound Action Potential).
True or False:
The strength of A-delta recruitment correlates with the degree of pain relief.
False
The strength of A-beta recruitment correlates with the degree of pain relief!
(not delta, despite A-delta and C fibres typically responsible carriers of pain information)
What part of the spinal cord do most fibres terminate in?
The dorsal horn
List the 4 cyclic components of the Spinal Cord Stimulation Process
Generate New Stimuli
Capture ECAP
Compare Amplitude with a set point
Calculate new Stimulation Current
(and re-cycle to start)
When comparing Level of Pain Relief to Neural Recruitment in Closed-Loop Control systems in SCS pain relief,
how does the Side Effect ‘line’ limit potential treatment?
With increasing neural recruitment, a side effect is that recruitment at greater elvels may be nociceptiveand reduce efficacy, at short and long intervals.
All development (Saluda Medical) has been focused on moving the side effect line, allowing an increase in amplitude to improve performance.
(see image)
Notes:
- Programming helps but not much
- The shape of the response curve determines the level of therapeutic effect; closed-loop control programming helps a lot (because lf slope of the response curve)
