Occipital nerve stimulation

The Evolution of Neuromodulation in the Treatment of Chronic Pain: Forward-Looking Perspectives

Background

The field of neuromodulation is continually evolving, with the past decade showing significant advancement in the therapeutic efficacy of neuromodulation procedures. The continued evolution of neuromodulation technology brings with it the promise of addressing the needs of both patients and physicians, as current technology improves and clinical applications expand.

Design

This review highlights the current state of the art of neuromodulation for treating chronic pain, describes key areas of development including stimulation patterns and neural targets, expanding indications and applications, feedback-controlled systems, noninvasive approaches, and biomarkers for neuromodulation and technology miniaturization.

Results and Conclusions

The field of neuromodulation is undergoing a renaissance of technology development with potential for profoundly improving the care of chronic pain patients. New and emerging targets like the dorsal root ganglion, as well as high-frequency and patterned stimulation methodologies such as burst stimulation, are paving the way for better clinical outcomes. As we look forward to the future, neural sensing, novel target-specific stimulation patterns, and approaches combining neuromodulation therapies are likely to significantly impact how neuromodulation is used. Moreover, select biomarkers may influence and guide the use of neuromodulation and help objectively demonstrate efficacy and outcomes.

Ventrolateral Tonsillar Position Defines Novel Chiari 0.5 Classification

BACKGROUND

Cervicomedullary compression in young children has been described in the context of Chiari type 1 malformation, with symptoms associated with the extent of tonsillar herniation below McRae line. Historically, Chiari type 1 malformation has been defined by tonsillar herniation of at least 5 mm. However, in certain populations, including very young children, Chiari symptoms may be present without this finding. A new Chiari classification is thus necessary.

METHODS

Cases involving patients up to 5 years of age evaluated for possible posterior fossa decompression were retrospectively reviewed. Preoperative symptoms, magnetic resonance imaging findings, surgical management, and short- and long-term outcome and follow-up were recorded. Tonsillar descent and presence of ventral herniation (VH) were recorded. We define VH as the tonsils crossing a line that bisects the caudal medulla at the level of the foramen magnum, thus creating a novel entity, Chiari type 0.5 malformation. Patients with ventrally herniated tonsils were compared with patients exhibiting more typical Chiari morphology.

RESULTS

Of 41 cases retrospectively reviewed, 20 met criteria for VH. These differed from cases without VH because of the predominance of medullary symptoms. In the VH cohort, 11 patients underwent surgical decompression with symptom resolution; 9 were initially managed conservatively, but 3 subsequently required surgery.

CONCLUSIONS

We define a novel Chiari entity, Chiari type 0.5 malformation, characterized by ventral tonsillar wrapping around the medulla in young children in the absence of classic Chiari type 1 malformation imaging findings. These patients are more likely to present with medullary symptoms than patients without VH. They are also more likely to require surgical decompression and respond favorably to intervention.

Neural Prosthetics:A Review of Empirical vs. Systems Engineering Strategies

Implantable electrical interfaces with the nervous system were first enabled by cardiac pacemaker technology over 50 years ago and have since diverged into almost all of the physiological functions controlled by the nervous system. There have been a few major clinical and commercial successes, many contentious claims, and some outright failures. These tend to be reviewed within each clinical subspecialty, obscuring the many commonalities of neural control, biophysics, interface materials, electronic technologies, and medical device regulation that they share. This review cites a selection of foundational and recent journal articles and reviews for all major applications of neural prosthetic interfaces in clinical use, trials, or development. The hard-won knowledge and experience across all of these fields can now be amalgamated and distilled into more systematic processes for development of clinical products instead of the often empirical (trial and error) approaches to date. These include a frank assessment of a specific clinical problem, the state of its underlying science, the identification of feasible targets, the availability of suitable technologies, and the path to regulatory and reimbursement approval. Increasing commercial interest and investment facilitates this systematic approach, but it also motivates projects and products whose claims are dubious.

Inhibitory effect of high-frequency greater occipital nerve electrical stimulation on trigeminovascular nociceptive processing in rats

Electrical stimulation of the greater occipital nerve (GON) has recently shown promise as an effective non-pharmacological prophylactic therapy for drug-resistant chronic primary headaches, but the neurobiological mechanisms underlying its anticephalgic action are not elucidated. Considering that the spinal trigeminal nucleus (STN) is a key segmental structure playing a prominent role in pathophysiology of headaches, in the present study we evaluated the effects of GON electrical stimulation on ongoing and evoked firing of the dura-sensitive STN neurons. The experiments were carried out on urethane/chloralose-anesthetized, paralyzed and artificially ventilated male Wistar rats. Extracellular recordings were made from 11 neurons within the caudal part of the STN that received convergent input from the ipsilateral facial cutaneous receptive fields, dura mater and GON. In each experiment, five various combinations of the GON stimulation frequency (50, 75, 100 Hz) and intensity (1, 3, 6 V) were tested successively in 10 min interval. At all parameter sets, preconditioning GON stimulation (250 ms train of pulses applied before each recording) produced suppression of both the ongoing activity of the STN neurons and their responses to electrical stimulation of the dura mater. The inhibitory effect depended mostly on the GON stimulation intensity, being maximally pronounced when a stimulus of 6 V was applied. Thus, the GON stimulation-induced inhibition of trigeminovascular nociceptive processing at the level of STN has been demonstrated for the first time. The data obtained can contribute to a deeper understanding of neurophysiological mechanisms underlying the therapeutic efficacy of GON stimulation in primary headaches.

Treatment of Allodynia by Occipital Nerve Stimulation in Chronic Migraine Rodent

BACKGROUND

Occipital nerve stimulation (ONS) is a therapy that benefits one-third of medically refractory chronic migraine (CM) patients. How ONS affects sensory thresholds and whether modulation of thresholds could predict which patients respond to the therapy remains unclear.

OBJECTIVE

To examine the effects of ONS on mechanical and thermal thresholds in a rodent CM model to better elucidate its mechanism of action.

METHODS

Male Sprague-Dawley rats were implanted bilaterally with electrodes to produce ONS. The CM cohort was infused with inflammatory media epidurally based on a validated model, whereas shams were not. Thresholds were evaluated with von Frey filaments and hot plate and thermode tests.

RESULTS

No baseline differences in sensory thresholds were found between the sham (n = 16) and CM (n = 16) groups. After headache induction, CM animals demonstrated mechanical allodynia in the occiput, periorbital region, forepaws, and hind paws (P < .05). In CM animals, ONS increased mechanical thresholds in all regions (P < .001), whereas in shams, it did not. ONS did not affect thermal thresholds in either group.

CONCLUSION

We show that ONS improves mechanical thresholds in a rodent CM model, but not in shams. Our finding that mechanical but not thermal thresholds are altered with ONS suggests a more significant modulation of A-α/β fibers than of C fibers. Assessing the ability of ONS to reduce mechanical thresholds during a trial period could potentially be used to predict which patients respond.

A good preoperative response to transcutaneous electrical nerve stimulation predicts a better therapeutic effect of implanted occipital nerve stimulation in pharmacologically intractable headaches

Occipital nerve stimulation (ONS) is a surgical approach to treat patients with medically intractable chronic headache disorders. However, no preoperative test has been yet validated to allow candidates to be selected for implantation. In this study, the analgesic efficacy of transcutaneous electrical nerve stimulation (TENS) was tested for 1 to 3 months in 41 patients with pharmacologically intractable headache disorders of various origins, using a new technique of electrode placement over the occipital nerve. ONS electrodes were subsequently implanted in 33 patients (occipital neuralgia [n=15], cervicogenic headache [n=7], cluster headache [n=6], chronic migraine [n=5]) who had responded at least moderately to TENS. Assessment was performed up to five years after implantation (three years on average), based on the mean and maximum daily pain intensity scored on a 0-10 visual analogue scale and the number of headache days per month. Both TENS and chronic ONS therapy were found to be efficacious (57-76% improvement compared to baseline on the various clinical variables). The efficacy of ONS was better in cases of good or very good preoperative response to TENS than in cases of moderate response to TENS. Implanted ONS may be a valuable therapeutic option in the long term for patients with pharmacologically intractable chronic headache. Although we cannot conclude in patients with poor or no response to TENS, a good or very good response to TENS can support the indication of ONS therapy. This preoperative test could particularly be useful in patients with chronic migraine, in whom it may be difficult to indicate an invasive technique of cranial neurostimulation.

Successful Management of Corneal Neuropathic Pain with Intrathecal Targeted Drug Delivery

OBJECTIVE

To describe the successful treatment of refractory corneal neuropathic pain with neuromodulation techniques.

DESIGN

Single case report.

SETTING

Academic tertiary care center in the United States of America.

SUBJECT AND METHODS

A 30-year-old woman presented with a 7-year history of refractory bilateral keratoneuralgia following laser-assisted in-situ keratomileusis (LASIK) procedure on both eyes. Having failed all conservative measures, the patient initially underwent trigeminal nerve stimulation and subsequently was implanted with an intrathecal drug delivery system (IDDS) with the catheter placed at the level C1.

RESULTS

Following an initial favorable response to the trigeminal nerve stimulator, the pain became refractory to neurostimulation after a few months and the system was explanted. The patient was successfully trialed with an intrathecal catheter placed at the level of C1 delivering a combination of bupivacaine and low dose fentanyl. The patient was then implanted with an IDDS equipped with a patient-activated bolus system. The patient was very satisfied with the treatment and has had greater than 50% pain relief for over a year.

CONCLUSIONS

Intrathecal delivery of bupivacaine and low dose fentanyl in the upper cervical spine can be effective in controlling refractory eye pain in properly selected patients and treatment centers.