Clinical Features

Ask the Expert: Dr Cormac Mullins

Dr Mullins was one of the keynote speakers at the recent Irish Pain Society’s Annual Scientific Meeting, where he provided an update on spinal cord stimulation, emphasising the importance of appropriate patient selection.

Dr Mullins also provided a useful critique of the very limited placebo-controlled RCT evidence base that currently exists for spinal cord stimulation, the large placebo response, and the need for more high quality RCTs in this area.

We spoke to Dr Mullins to gain further insights into his valuable work and career to date.

Can you give our readers a brief background of your career to date?

I started as a consultant in anaesthesiology and pain medicine at Cork University Hospital and South Infirmary Victoria University Hospital just over a year ago. Before that, I was working as a pain consultant in Guy’s and St. Thomas’s NHS Trust in London for a year, where I also did my fellowship training. I am from Galway originally and trained in Trinity College Dublin and completed my anaesthesiology training in Ireland. I also did a pain fellowship at St. James’s Hospital Dublin before going to London. My fellowship training was in the area of spinal cord stimulation which is an implantable device which can be very successful for treating certain types of chronic pain. I trained at one of the biggest centres in Europe for this form of therapy and am excited to bring this expertise to Ireland.

Tell us a bit more about your current research work

My main area of research is in the area of spinal cord stimulation (SCS) and headache.

Spinal cord stimulation (SCS) is a form of therapeutic neuromodulation. It was defined by the International Neuromodulation Society as “the alteration of the nerve activity through targeted delivery of a stimulus, such as an electrical stimulation or chemical agents, to specific neurological sites in the body”.

I published three papers in the last year on the topic of SCS.1-3 These were interesting papers that looked at certain areas such as MRI conditionality of devices at follow up (which is a very important consideration for patients undergoing SCS implantation as MRIs are so accessible these days), migration of SCS leads during trials and combined implantation of SCS with dorsal root ganglion stimulation which can provide additional flexibility and therapeutic alternatives for spinal cord stimulation. I also published a paper on the use of lignocaine infusions as a treatment for primary headache disorders, such as migraine, and trigeminal neuralgia and this was shown to be quite effective in those refractory to other therapies.4 I also have a review paper on neuromodulation options in migraine and other headache disorders coming out soon. This can provide a non-drug alternative for those who have a condition such as migraine and cannot tolerate medication.

What are your hopes for 2024 for Pain Medicine and Anaesthesiology?

My hopes are to deliver effective multidisciplinary pain management strategies to the greatest number of people while tackling the waiting list for chronic pain services in Ireland. We are hoping that we can deliver evidencebased treatment approaches which focus on enhancing selfmanagement for patients with chronic pain in Cork and improve the throughput and quality of care delivered in our service.

Can you outline some of the biggest challenges facing this field for 2024 and the key opportunities?

In Ireland, the biggest challenge is undoubtedly access to multidisciplinary pain management strategies in a timely fashion. The waiting lists in Ireland for pain medicine are far too long and in Cork we are hoping to redesign how we see patients. We are really excited to have a few excellent new additions to our department in Cork in the form of specialist physiotherapists and a clinical psychologist and we need to focus on getting the message out there for those with chronic pain to remain active, continue with usual activities and not let pain take over. Key management principles that are covered in pain-management programmes involve establishing what is important to the individual and continuing to take committed action towards these goals in spite of chronic pain. Unfortunately, there is often an over-reliance on medical approaches to chronic pain and a key challenge involves moving beyond this to a more integrated and holistic model and taking a person-centred approach to care.

How does Ireland compare with the rest of Europe at present Pain Medicine and Anesthesiology?

In my experience, I believe we are only just catching up to the message that chronic pain needs to be treated with a multidisciplinary team of medical and nursing professionals, physiotherapists and psychologists and this is mirrored in chronic pain clinics across Ireland that have insufficient numbers of multidisciplinary staff. We are lucky in Cork to have made recent appointments that will allow us to become a true multidisciplinary pain clinic with clinicians from different specialities working together in the same space and communicating with each other frequently to deliver coordinated, patient-centred and evidencebased care.

I am optimistic about the quality of the pain training programme that exists in Ireland now that will rival any pain medicine training programme in Europe and that this will deliver the highest quality pain medicine consultants in the future.

What would be your personal goals and hopes for this field in the future?

My personal goals include tackling the waiting lists for chronic pain in Ireland, delivering effective evidence-based multidisciplinary to the greatest volume of patients, removing the siloed approach to back pain within medicine and exploring cross-speciality therapeutic approaches. I am hopeful that in a year’s time that significant dents will have been made in the waiting times for patients to access care and that the quality of care they will receive will be truly multidisciplinary and evidence-based. I am hopeful that we can deliver advanced pain management modalities to those who will benefit from it, including spinal cord stimulation, and we are keen to re-establish this service in Cork this year.

Some of Dr Mullins published scientific papers include:

A retrospective review of elevated lead impedances in impedance-dependent magnetic resonance-conditional spinal cord stimulation devices

Advances in Spinal cord stimulation (SCS) device technology in recent years have led to the development of SCS systems that are magnetic resonance imaging (MRI)conditional, most of which are dependent on normal lead impedances. The objective of this study was to retrospectively analyze the rate of elevated lead impedance in these devices to determine the rate of failure of MRconditional modes.

This was a single-center, retrospective, chart-based review conducted during a five-year period. Patients were included if they had been implanted with an impedance-dependent MR-conditional SCS and had a documented impedance check at least 6 months after implantation. A Kaplan-Meier survival analysis was performed to map the survival of MR-conditionality over time.

There were 363 cases included between 2015 and 2020, which corresponded to a total of 602 SCS leads. Nevro was the most common manufacturer (67.8%), followed by Boston Scientific (22.3%) and Abbott (9.9%). The average overall follow-up time was 2.25 years. Overall, 67 (18.5%) of patients had lead impedances over 10,000 Ω at follow-up with a total of 186 electrode contacts (3.9%). Leads most commonly had either one (40%), two (22%) or three (12%) electrode contacts out of range. Risk of failure of lead impedances increased by 35.4% with each successive year to a peak of 43% of all leads by year 5. Mean overall survival time of normal lead impedances was 4.77 years (CI 4.40-5.13). There was no statistically significant difference in mean overall survival time between Abbott (M = 4.0 years, SD = 1.25), Boston Scientific (M = 4.64 years, SD = 1.75) and Nevro (M = 4.80 years, SD = 3.28), χ2 (2, N = 358) = 1.511, p = 0.47; however, Abbott leads had a greater total number of failed impedance contacts (50/568, 8.8%), in comparison to Nevro (124/3064, 4.0%), χ2 (1, N = 3630) = 23.76, p < 0.00001, at a similar follow-up time.

This retrospective study identified elevated impedances in 18.5% of MR-conditional SCS devices at an average of 2.25 years follow-up resulting in loss of MRconditionality and a mean overall lead survival time of 4.77 years for normal lead impedance.

Radiographic lead migration in percutaneous spinal cord stimulator trials rapm/early/2023/07/20/rapm2023-104347.full.pdf

Lead migration during spinal cord stimulator (SCS) trials is relatively neglected in the literature and presents a different set of challenges compared with fully implanted leads. There is no consensus on what constitutes a clinically significant amount of radiographic lead migration during SCS trials. We wished to evaluate the incidence and extent of radiographic lead migration during percutaneous SCS trials, to investigate the risk factors for lead migration and whether this has impacted on trial success.

This prospective observational study of percutaneous SCS trials took place in a tertiary referral center in the UK between April 2021 and January 2022. Radiographs of SCS lead position were taken at baseline and prior to lead removal. Lead migration ≥50% of a vertebral level was deemed significant.

One hundred trials were included comprising 162 leads. Mean migration distance was 0.55 vertebral levels (SD 0.85) or 12.5 mm (SD 18.2) in a caudal direction. Significant radiographic migration occurred in 50% of all leads (81 of 162 leads), at least one lead in 62% of cases and all leads in 44% of cases.

Radiographic lead migration was not found to be associated with reduced trial success. A single lead and mechanical anchors were associated with greater incidence of lead migration.

Radiographic lead migration of approximately half of a vertebral level in a caudal direction can be expected during percutaneous SCS trials and this can be anticipated by siting leads half of a vertebral level higher to accommodate for this. Additional factors should be considered in the setting of radiographic lead migration to determine whether this can be considered clinically significant.

Effectiveness of Combined Dorsal Root Ganglion and Spinal Cord Stimulation: A Retrospective, Single-Centre Case Series for Chronic Focal Neuropathic Pain Effectiveness of Combined Stimulation

This case series retrospectively reviewed the outcomes in patients implanted with combined, synchronous dorsal root ganglion stimulation (DRGS) and spinal cord stimulation (SCS) connected to a single implantable pulse generator (IPG) in a tertiary referral neuromodulation centre in the United Kingdom. Materials and Methods Twenty-six patients underwent a trial of DRGS+SCS for treating focal neuropathic pain between January 2016 and December 2019, with a follow-up in February 2022. A Transgrade approach was employed for DRGS. Patients were provided with three possible stimulation programmes: DRGS-only, SCS-only, or DRGS+SCS. Patients were assessed for pain intensity, patients’ global impression of change (PGIC), preferred lead(s) and complications. Results Twenty patients were successful and went on for full implantation. The most common diagnosis was Complex Regional Pain Syndrome. After an average of 3.1 years follow-up, one patient was lost to follow-up, and two were non-responders. Of the remaining 17 patients, 16 (94%) continued to report a PGIC of 7. The average pain intensity at Baseline was 8.5 on an NRS scale of 0-10. At the last follow-up, the average NRS reduction overall was 78.9% with no statistical difference between those preferring DRGS+SCS (n = 9), SCS-only (n = 3) and DRGS-only (n = 5). The combination of DRGS+SCS was preferred by 53% at the last follow-up. There were no serious neurological complications. Conclusion This retrospective case series demonstrates the potential effectiveness of combined DRGS+SCS with sustained analgesia observed at an average follow-up of over three years. Implanting combined DRGS+SCS may provide programming flexibility and therapeutic alternatives.

A single infusion of intravenous lidocaine for primary headaches and trigeminal neuralgia: a retrospective analysis https://pubmed.ncbi.nlm.nih. gov/37638187/

Intravenous (IV) lidocaine has been used as a transitional treatment in headache and facial pain conditions, typically as an inpatient infusion over several days, which is costly and may increase the risk of adverse effects. Here we report on our experience using a single one-hour IV lidocaine infusion in an outpatient day-case setting for the management of refractory primary headache disorders with facial pain and trigeminal neuralgia. This is a retrospective, singlecenter analysis on patients with medically refractory headache with facial pain and trigeminal neuralgia who were treated with IV lidocaine between March 2018 and July 2022. Lidocaine 5 in 60 mL saline was administered over 1 h, followed by an observation period of 30 min. Patients were considered responders if they reported reduction in pain intensity and/or headache frequency of 50% or greater. Duration of response was defined as short-term (< 2 weeks), medium-term (2-4 weeks) and long-term (> 4 weeks).

Forty infusions were administered to 15 patients with trigeminal autonomic cephalalgias (n = 9), chronic migraine (n = 3) and trigeminal neuralgia (n = 3).

Twelve patients were considered responders (80%), eight of whom were complete responders (100% pain freedom). The average duration of the treatment effect for each participant was 9.5 weeks (range 1-22 weeks). Six out of 15 patients reported mild and selflimiting side effects (40%).

A single infusion of IV lidocaine might be an effective and safe transitional treatment in refractory headache conditions with facial pain and trigeminal neuralgia. The sustained effect of repeated treatment cycles in some patients may suggest a role as long-term preventive therapy in some patients.

Dr Cormac Mullins is a Consultant Pain Specialist and Anaesthesiologist in Cork University Hospital and the South Infirmary Victoria University Hospital, Cork

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