The rebellious chronic neuropathic pain of the lower limbs (including the sequelae
lumbosciatica) causes a major functional repercussion and an impairment of the quality of
life. Spinal cord stimulation (SCS) is offered when other treatments are ineffective or
insufficient (K. Kumar et al., 2007). This technique has been used in routine care for
over 20 years, with a well-established clinical benefit for these indications, and
recognized by HAS (see 2014 recommendations in appendix 1). Moreover, recent technical
progress has made it possible to provide better user comfort for implanted patients, in
particular with new stimulation methods that best adapt to the activities and feelings of
the patients (De Ridder & Vanneste, 2016; V . Kumar et al., 2018).
The therapeutic objectives defined between the candidate patient for EMS and the Pain
team are part of a personalized rehabilitation and reintegration process. This is to
reduce the pain felt by the patient but also the functional impact, by gradually resuming
activity, taking into account the specific situation of each patient. Functional
limitation depends on several factors, such as exercise deconditioning but also fear of
movement that is essential to assess in patients who are candidates for EMS. Patient care
involves an assessment made by a trained multi-professional team in which the role of the
pain coordinator (IDEC) is central, with therapeutic education work through regular
physical and telephone consultations. Self-administered questionnaires analyzing
functional abilities, quality of life and pain are currently being used for the pre- and
post-operative assessment of patients undergoing EMS. Although they are a diagnostic and
decision-making tool, they nevertheless correspond to a subjective assessment of the
patient of his abilities as he sees them, and not to an assessment of his actual
objective abilities. Thus, despite the technical progress represented by the new
stimulation methods, the perioperative assessment of patients treated for EMS lacks
personalized tools.
The recent development of technological tools that are easy to use on a daily basis, such
as activity trackers and smartwatches, is an attractive option in chronic pathologies,
but still insufficiently used in current medical practice. A review of the literature has
shown the value of the use of activity trackers, particularly in postoperative follow-up
and functional rehabilitation (Appelboom et al., 2016), and in low back pain patients
(GORDON & BLOXHAM, 2017 ). Another study evaluating the data collected by an actimeter
integrated into a stimulation generator compared to the patient's verbal report on his
activities reports an overestimation of the functional impact by patients in
self-evaluation (Goudman et al., 2018). Likewise, a study on the evaluation of the
quality of sleep highlighted a difference between the feelings reported by the patient,
the self-questionnaires and the data recorded in polysomnography (Jaeger et al., 2019),
with a trend to increase sleep disorders. All of these studies confirm the limits in
terms of the reliability of declarative data and the need for objective measures to
assess the symptoms of patients in chronic conditions.
In addition, some of these devices have recently made it possible to evaluate the vmHRV
(vagally-mediated Heart Rate Variability) index (Hernando et al., 2018). This
physiological index has been studied for MOTIVE_Protocole_v1_20200610 HBD_2020_23 IDRCB
2020-A01731-38 11/40 several years, and has shown its interest in various chronic
pathologies such as depression, cardiovascular pathologies, fibromyalgia (Kemp et al.,
2010). Thus, compared to healthy control subjects, patients with chronic pain have a
decreased vmHRV index linked to lower vagal activity (Koenig et al., 2016). In addition,
in chronic pain patients, a correlation was observed between taking analgesics, the
impact of pain on daily life and a significantly reduced vmHRV index. Moreover, patients
with little relief from drug treatment had the lowest vmHRV index (Koenig et al., 2015),
thus showing a link between this index and the severity of chronic pain, its daily
impact, l effectiveness of drug treatment. Likewise, a correlation has been demonstrated
between the degree of catastrophization of pain in patients and the vmHRV index (Koenig
et al., 2016). Finally, a recent review of the imaging data associated with the
measurement of the HRV index suggests a link between functional connectivity and the
activity of certain brain regions (ventral striatum, anterior cingulate cortex, medial
pre-frontal cortex, putamen ), the ability to manage stress and emotions, and the HRV
index (Thayer et al., 2012), thus proposing a neurovisceral integration model. The vmHRV
index can therefore be considered as an objective marker in the assessment of emotional
and physiological coping skills in a patient with chronic pain. This aspect is crucial in
the evaluation and management of these patients, and more particularly when an invasive
therapy is envisaged such as EMS.
Finally, the development of certain imaging sequences makes it possible to study the
anatomical (diffusion tensor sequences: DTI) and functional (functional MRI sequences)
connectivity in regions of interest in patients, in particular at rest (Fox & Raichle,
2007). During nociceptive stimulation, the functional activation of certain regions of
interest was demonstrated, grouped together under the term "pain matrix": insula, primary
and secondary somatosensory cortex, thalamus, anterior cingulate cortex, pre- frontal,
tonsil and peri-acqueductal gray matter (Apkarian et al., 2005; Leknes & Tracey, 2008).
Chronic pain alters the functioning of neural circuits in these regions, leading to
changes in connectivity and activity observable in neuroimaging (Baliki et al., 2012;
Wood et al., 2007). A prospective study conducted in 39 patients has also shown the
predictive character of some of these changes during the chronicization of pain in a
cohort of patients suffering from subacute low back pain (Baliki et al., 2012): patients
developing pain patients (which lasts beyond 6 months) immediately presented an
alteration in the functioning of the neural circuits involved in motivation, with a
stronger anatomical and functional connectivity between the nucleus accumbens and the
medial pre-frontal cortex, compared to the patients recovering from the subacute episode.
Since then, other studies have suggested a link between the process of pain
chronicization and changes in the anatomical and functional connectivity of
cortico-striated circuits involved in cognitive and motivational aspects (Navratilova &
Porreca, 2014). Activation of the meso-limbic motivational and reward circuit has also
been shown to be involved in the perception of pain relief (Leknes et al., 2011;
Navratilova et al., 2012; Seymour et al., 2005) .
The interest of these new cardiac markers (HRV), radiological (anatomical and functional
connectivity in MRI) and activity (connected watch) in the management of patients
eligible for stimulation medullary will be evaluate. The use of a connected watch
continuously measuring activity (number of steps, distance covered), sleep (duration of
deep and light sleep, number of nocturnal awakenings), and the HRV index could provide an
objective assessment and complementary to the self-questionnaires and the usual
interviews. The MRI profile of anatomical and functional connectivity in the regions of
interest linked to chronic pain and motivation in patients treated for EMS, would allow
to seek a link between functional outcome, motivation and the ability to adapt and manage
stress.
By combining the usual care of patients eligible for an EMS with measurements of the HRV
index, objective measurements of activity (number of steps, quality of sleep), and
connectivity measurements obtained on MRI, the collection of preliminary data to identify
markers correlated with the effectiveness of EMS will be possible. Ultimately, these
markers could be used to optimize the perioperative management of these patients.