Paresthesia thresholds in spinal cord stimulation: a comparison of theoretical results with clinical data

The potential distributions produced in the spinal cord and surrounding tissues by dorsal epidural stimulation at the midcervical, midthoracic, and low thoracic levels were calculated with the use of a volume conductor model. Stimulus thresholds of myelinated dorsal column fibers and dorsal root fibers were calculated at each level in models in which the thickness of the dorsal cerebrospinal fluid (CSF) layer was varied. Calculated stimulus thresholds were compared with paresthesia thresholds obtained from measurements at the corresponding spinal levels in patients. The influences of the CSF layer thickness, the contact separation in bipolar stimulation and the laterality of the electrodes on the calculated thresholds were in general agreement with the clinical dat

Is there a "safety zone" in the mandibular premolar region where damage to the mental nerve can be avoided if periapical extrusion occurs?

The mandibular premolars are located close to the mental foramina (Fig. 1). As such, various events affecting these teeth, such as odontogenic infection1 and orthodontic, endodontic, periodontal or surgical misadventure, may result in neurosensory disturbance of the mental nerves.2-4 In one retrospective study, the incidence of mental paresthesia resulting from periapical infection or pathology was 0.96. In another 0.24 of cases in the same study, mental paresthesia was a complication of root canal treatment (caused by severe overfill in one case and iatrogenic perforation of mechanical instrumentation through the root and into the mental nerve in the second case).1 The incidence of mental paresthesia resulting from orthodontic, periodontal and surgical misadventure cannot be determined but is presumably low, as most such cases have been reported as individual case reports. In endodontology, elimination of infection from the pulp and dentin followed by adequate intracanal preparation and proper sealing constitute the basic principles of root canal treatment. Ideally, mechanical preparation and filling should be limited to the root canal, as overinstrumentation or extrusion of chemical fillings beyond the apical foramen to the adjacent nerve may give rise to neurosensory disturbances such as anesthesia, paresthesia or dysesthesia.5 Unfortunately, cases of endodontic extrusion of various filling or irrigation agents continue to be reported, despite recent advances in endodontology

Estimation of fiber diameters in the spinal dorsal columns from clinical data

Lack of human morphometric data regarding the largest nerve fibers in the dorsal columns (DCs) of the spinal cord has lead to the estimation of the diameters of these fibers from clinical data retrieved from patients with a new spinal cord stimulation (SCS) system. These patients indicated the perception threshold of stimulation induced paresthesia in various body segments, while the stimulation amplitude was increased. The fiber diameters were calculated with a computer model, developed to calculate the effects of SCS on spinal nerve fibers. This computer model consists of two parts: (1) a three-dimensional (3-D) volume conductor model of a spinal cord segment in which the potential distribution due to electrical stimulation is calculated and (2) an electrical equivalent cable model of myelinated nerve fiber, which uses the calculated potential field to determine the threshold stimulus needed for activation. It is shown that the largest fibers in the medial DCs are significantly smaller than the largest fibers in the lateral parts. This finding is in accordance with the fiber distribution in cat, derived from the corresponding propagation velocities. Moreover, it is shown that the mediolateral increase in fiber diameter is mainly confined to the lateral parts of the DCs. Implementation of this mediolateral fiber diameter distribution of the DCs in the computer model enables the prediction of the recruitment order of dermatomal paresthesias following increasing electrical stimulation amplitud

Paresthesia

Paresthesias are spontaneous or evoked abnormal sensations of tingling, burning, pricking, or numbness of a person's skin with no apparent long-term physical effect. Patients generally describe a lancinating or burning pain, often associated with allodynia and hyperalgesia. The manifestation of paresthesia can be transient or chronic. Transient paresthesia can be a symptom of hyperventilation syndrome or a panic attack, and chronic paresthesia can be a result of poor circulation, nerve irritation, neuropathy, or many other conditions and causes. This book is written by authors that are respected in their countries as well as worldwide. Each chapter is written so that everyone can understand, treat and improve the lives of each patient

Perception threshold and electrode position for spinal cord stimulation

The perception threshold for epidural spinal cord stimulation in chronic pain management was analyzed on 3923 testing data obtained from 136 implanted patients. The initial areas of paresthesiae due to stimulation were recorded and reported as the stimulation map according to the location of electrodes. Measurement of dorsal thickness of the cerebrospinal fluid (CSF) layer was obtained from 26 subjects using magnetic resonance imaging (MRI). The results indicate that the perception threshold is a function of the spinal level of the implanted electrodes, of the mediolateral position in the spinal canal and the contact separation of electrode. Differences in perception threshold at various vertebral levels are mainly due to varying depths of the dorsal CSF layer. The medially placed electrodes caudal to the mid-cervical levels have a higher perception threshold than more laterally placed ones. The electrodes at high and mid-cervical levels, however, have a smaller perception threshold if placed medially. The information obtained from this investigation has important implications for the design of a new-generation stimulation system and clinical application to maximize the longevity of the power source

Decompression of inferior alveolar nerve: case report comment

Paresthesia as a result of mechanical trauma is one of the most frequent sensory disturbances of the inferior alveolar nerve. This case report describes surgical treatment for paresthesia caused by a compressive phenomenon within the mandibular canal. The cause of the compression, a broken instrument left in the patient's mouth during previous endodontic therapy, was identified during routine radiography and computed tomography. Once the foreign object was removed by surgery, the paresthesia resolved quickly. This case highlights the potential for an iatrogenic mechanical cause of paresthesia. Comment : The article by Marques and Gomes (J Can Dent Assoc 2011;77:b34) caught my attention. For your information, there is almost an almost similar case reported recently, but with dysesthesia.1 It is fortunate that the patient in the current case has less severe symptoms (occasional numbness of her left lip and a small part of her chin, and a tingling sensation in the vestibular gingival). What I can deduce from the radiographs shown is that the file was actually lodged onto the wall of the periapical defect and the mandibular canal, and because of this the inferior alveolar nerve (IAN) was spared direct injury. Ikeda et al.2 had shown that there is room between the IAN and the canal. However, as reported by the Marques and Gomes, her symptoms were more aggravated in the morning and during stressful situations. This may be a result of fluid accumulation in the morning, or during any sympathetic (stressful) event, that may result in vasodilatation, and hence compression within the narrow mandibular canal that usually average 3.4 + 0.5 mm in diameter. 2,3 I hope this opinion is of help. Thank you

The Ultimate Poker Face: A Case Report of Facial Diplegia, a Guillain-Barré Variant

Introduction: Facial diplegia, a rare variant of Guillain-Barré syndrome (GBS), is a challenging diagnosis to make in the emergency department due to its resemblance to neurologic Lyme disease.Case report: We present a case of a 27-year-old previously healthy man who presented with bilateral facial paralysis.Discussion: Despite the variance in presentation, the recommended standard of practice for diagnostics (cerebrospinal fluid albumin-cytological dissociation) and disposition (admission for observation, intravenous immunoglobulin, and serial negative inspiratory force) of facial diplegia are the same as for other presentations of GBS.Conclusion: When presented with bilateral facial palsy emergency providers should consider autoimmune, infectious, idiopathic, metabolic, neoplastic, neurologic, and traumatic etiologies in addition to the much more common neurologic Lyme disease

Spinal cord stimulation: fiber diameters in the dorsal columns modeled from clinical data

Computer simulations of clinical data were performed to estimate the diameter distribution of A¿ß nerve fibers in the human dorsal columns, activated by spinal cord stimulation. Qualitatively, the calculated distribution was in accordance with experimental data. Due to mismatches in impedance and limited resolution of the CT scans more patient data is needed to reliably predict the quantitative diameter distributio

Spinal cord stimulation in chronic pain: evidence and theory for mechanisms of action.

Well-established in the field of bioelectronic medicine, Spinal Cord Stimulation (SCS) offers an implantable, non-pharmacologic treatment for patients with intractable chronic pain conditions. Chronic pain is a widely heterogenous syndrome with regard to both pathophysiology and the resultant phenotype. Despite advances in our understanding of SCS-mediated antinociception, there still exists limited evidence clarifying the pathways recruited when patterned electric pulses are applied to the epidural space. The rapid clinical implementation of novel SCS methods including burst, high frequency and dorsal root ganglion SCS has provided the clinician with multiple options to treat refractory chronic pain. While compelling evidence for safety and efficacy exists in support of these novel paradigms, our understanding of their mechanisms of action (MOA) dramatically lags behind clinical data. In this review, we reconstruct the available basic science and clinical literature that offers support for mechanisms of both paresthesia spinal cord stimulation (P-SCS) and paresthesia-free spinal cord stimulation (PF-SCS). While P-SCS has been heavily examined since its inception, PF-SCS paradigms have recently been clinically approved with the support of limited preclinical research. Thus, wide knowledge gaps exist between their clinical efficacy and MOA. To close this gap, many rich investigative avenues for both P-SCS and PF-SCS are underway, which will further open the door for paradigm optimization, adjunctive therapies and new indications for SCS. As our understanding of these mechanisms evolves, clinicians will be empowered with the possibility of improving patient care using SCS to selectively target specific pathophysiological processes in chronic pain

Effects of electrode configuration and geometry on fiber preference in spinal cord stimulation

In contrast to the widespread assumption that dorsal column fibers are the primary targets of spinal cord stimulation by a dorsal epidural electrode, it appears that dorsal root fibers are recruited as well, and even preferentially under various conditions. This will, however, limit the coverage of the painful body areas with paresthesia, a prerequisite for the management of chronic pain. In order to favor the preferential stimulation of dorsal column fibers, advantage was taken of the different positions and orientations of fibers in the dorsal columns and dorsal roots. Using an SCS computer model, electrode configurations have been designed for the selective stimulation of the human dorsal column