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.