Jeffrey E. Arle

Surgical treatment of common entrapment neuropathies in the upper limbs

Entrapment neuropathies of the upper extremity are common, debilitating conditions. Most patients with these neuropathies are readily diagnosed on purely clinical grounds and may be effectively managed with nonoperative measures. However, the broad differential diagnosis often necessitates electrodiagnostic testing and radiographic imaging to clarify the situation. This review focuses on three of the most common entrapment neuropathies in the upper limbs: carpal tunnel syndrome (median nerve entrapment at the wrist), cubital tunnel syndrome (ulnar nerve entrapment at the elbow), and radial tunnel syndrome (posterior interosseous nerve entrapment). Anatomical considerations, patient evaluation, indications for surgical intervention, options for surgical approaches, outcomes, and complications are discussed.

An application of fractal dimension to the detection of transients in the electroencephalogram

It is sometimes desirable to identify a brief seizure, occasional spike, single evoked potential, or other transient in the EEG. Transient detection in an EEG can be a difficult task, often requiring prior knowledge of the characteristics of the transient. A fractal is a shape which retains structural detail despite magnification (scaling). The complexity of the structure of such a set, invariant under this scaling, can be characterized by a single number: the fractal dimension. Regarding the EEG as a fractal, we have shown that transient deterministic data in the EEG have a fractal dimension different from the quasirandom background. An extensive introduction to fractals is presented with the assumption that the reader is unfamiliar with the theory. In the preliminary results presented here, analysis by fractal dimension is shown to be a promising method of transient detection, requiring no prior knowledge of the characteristics of the transient. Possible applications of the technique to evoked potential technology and epilepsy surgery are discussed. Other applications to biology, neuroscience and medicine are reviewed.

Neural modeling of intrinsic and spike-discharge properties of cochlear nucleus neurons

The purpose of this study was to develop neurobiologically plausible models to account for the response properties of several types of cochlear nucleus neurons. Three cell types — the bushy cells, stellate cells, and fusiform cells — were selected because useful data from intracellular recordings were available for these cell types, and because these three cell types exhibit distinct contrasts in their neuronal signal coding strategies. Stellate cells have primarily linear current-voltage (I–V) characteristics, but both bushy and fusiform cells have highly non-linear I–V characteristics. In light of this, we hypothesize that some of these cells have non-linear voltage-dependent conductances which alter their response properties. We modeled the bushy cell membrane conductance as an exponentially increasing function of membrane voltage, that of the fusiform cell as an exponentially decreasing function of the voltage, and that of the stellate cell as being voltage-independent.We have combined the voltage-dependent non-linear conductances of the cell membrane with a simple R-C circuit type of neuron model. These models reproduced the salient features of the experimentally observed I–V characteristics of the cells. In addition, we found that the models reproduced the spike discharge behavior to intracellularly injected current steps. Moreover, a more detailed study of stellate cell ‘chopper’-type response patterns yielded hypotheses regarding the nature of the current that must exist at the soma during a pure-tone stimulus in order for the cells to exhibit various chopper subtype patterns, such as chop-S, chop-T, and Oc.The chop-S pattern requires a steady average current level with a relatively small variability during the tone-burst stimulus. The chop-T pattern, in contrast, requires that the current become more irregular during the tone-burst stimulus. The Ocpattern arises, however, when the input is similar to the chop-T case but the intrinsic properties of the cell model have been changed to increase the accommodation of the threshold. The implications of these findings for circuitry in the cochlear nucleus are discussed.Our analysis of these models revealed that this approach can be used to simulate neuronal cell types where I-V characteristics are known but more detailed ion channel data are not known.

Motor cortex stimulation for pain and movement disorders

SummarySince initial reports in the early 1990s, stimulation of the Ml region of the cortex (MCS) has been used to treat chronic refractory pain conditions and a variety of movement disorders. A Medline search of literature between 1991 and 2007 revealed 512 cases using MCS. Although most of these relate to the treatment of pain (422), 84 of them involve movement disorders. More recently, several studies have specifically looked at treating Parkinson’s disease (PD) with MCS. We report here several of our own cases using MCS to treat post-stroke and non-poststroke pain syndromes and movement disorders (n = 8), PD (n = 4), ET (n = 2), and cortico-basal degeneration (n = 1). We also cover the essential history of this procedure and our current research using computational modeling to understand further the underlying mechanisms of MCS.

Successful bilateral deep brain stimulation of the globus pallidus internus for persistent status dystonicus and generalized chorea

The authors report the cases of 2 young male patients (aged 16 and 26 years) with dystonic cerebral palsy of unknown origin, who developed status dystonicus, an acute and persistent combination of generalized dystonia and chorea. Both patients developed status dystonicus after undergoing general anesthesia, and in 1 case, after administration of metoclopramide. In attempting to control this acute hyperkinetic movement disorder, multiple medication trials failed in both cases and patients required prolonged intubation and sedation with propofol. Bilateral deep brain stimulation of the globus pallidus internus (4 and 2 months after the onset of symptoms in the first and second case, respectively) produced immediate resolution of the hyperkinetic movement disorder in each case. Deep brain stimulation provided persistent suppression of the dystonic movement potential after a follow-up of 30 and 34 months, respectively, as demonstrated by the reemergence of severe dystonia during the end of battery life of the implantable pulse generators that was readily controlled by exchange of the generators in each case.

Motor cortex stimulation in patients with Parkinson disease: 12-month follow-up in 4 patients

OBJECT Since the initial 1991 report by Tsubokawa et al., stimulation of the M1 region of cortex has been used to treat chronic pain conditions and a variety of movement disorders. METHODS A Medline search of the literature published between 1991 and the beginning of 2007 revealed 459 cases in which motor cortex stimulation (MCS) was used. Of these, 72 were related to a movement disorder. More recently, up to 16 patients specifically with Parkinson disease were treated with MCS, and a variety of results were reported. In this report the authors describe 4 patients who were treated with extradural MCS. RESULTS Although there were benefits seen within the first 6 months in Unified Parkinsons Disease Rating Scale Part III scores (decreased by 60%), tremor was only modestly managed with MCS in this group, and most benefits seen initially were lost by the end of 12 months. CONCLUSIONS Although there have been some positive findings using MCS for Parkinson disease, a larger study may be needed to better determine if it should be pursued as an alternative surgical treatment to DBS.

Heuristic map of myotomal innervation in humans using direct intraoperative nerve root stimulation.

OBJECTIVE Considerable overlap exists in nerve root innervation of various muscles. Knowledge of myotomal innervation is essential for the interpretation of neurological examination findings and neurosurgical decision-making. Previous studies relied on cadaveric dissections, animal studies, and cases with anomalous anatomy. This study investigates the myotomal innervation patterns of cervical and lumbar nerve roots through in vivo stimulation during surgeries for spinal decompression. METHODS Patients undergoing cervical and lumbar surgeries in which nerve roots were exposed in the normal course of surgery were included in the study. Electromyography electrodes were placed in the muscle groups that are generally accepted to be innervated by the roots under study. These locations included levels above and below the spinal levels undergoing decompression. After decompression, a unipolar neural stimulator probe was placed directly on the nerve root sleeve and constant current stimulation in increments of 0.1 mA was performed. Current was raised until at least a 100 μV amplitude-triggered electromyographic response was noted in 1 or more muscles. All muscles that responded were recorded. RESULTS A total of 2295 nerve root locations in 129 patients (mean age 57 ± 15 years, 47 female [36%]) were stimulated, and 1589 stimulations met quality criteria and were analyzed. Four hundred ninety-five stimulations were performed on roots contributing to the cervical and brachial plexus from C-3 to T-1 (31.2%), and 1094 (68.8%) were roots in the lumbosacral plexus between L-1 and S-2. The authors were able to construct a statistical map of the contributions of each cervical and lumbosacral nerve root for the set of muscle groups monitored in the protocol. In many cases the range of muscles innervated by a specific root was broader than previously described in textbooks. CONCLUSIONS This is the largest data set of direct intraoperative nerve root stimulations during decompressive surgery, demonstrating the relative contribution of root-level motor input to various muscle groups. Compared with classic neuroanatomy, a significant number of roots innervate a broader range of muscles than expected, which may account for the variability of presentation between patients with identical number and location of compressed roots.

Rhythmic movement in Parkinson's disease: effects of visual feedback and medication state

Previous studies examining discrete movements of Parkinson’s disease (PD) patients have found that in addition to performing movements that were slower than those of control participants, they exhibit specific deficits in movement coordination and in sensorimotor integration required to accurately guide movements. With medication, movement speed was normalized, but the coordinative aspects of movement were not. This led to the hypothesis that dopaminergic medication more readily compensates for intensive aspects of movement (such as speed), than for coordinative aspects (such as coordination of different limb segments) (Schettino et al., Exp Brain Res 168:186–202, 2006). We tested this hypothesis on rhythmic, continuous movements of the forearm. In our task, target peak speed and amplitude, availability of visual feedback, and medication state (on/off) were varied. We found, consistent with the discrete-movement results, that peak speed (intensive aspect) was normalized by medication, while accuracy, which required coordination of speed and amplitude modulation (coordinative aspect), was not normalized by dopaminergic treatment. However, our findings that amplitude, an intensive aspect of movement, was also not normalized by medication, suggests that a simple pathway gain increase does not act to remediate all intensive aspects of movement to the same extent. While it normalized movement peak speed, it did not normalize movement amplitude. Furthermore, we found that when visual feedback was not available, all participants (PD and controls) made faster movements. The effects of dopaminergic medication and availability of visual feedback on movement speed were additive. The finding that movement speed uniformly increased both in the PD and the control groups suggests that visual feedback may be necessary for calibration of peak speed, otherwise underestimated by the motor control system.

Pupil-sparing third nerve palsy with preoperative improvement from a posterior communicating artery aneurysm

BACKGROUND Despite the plenitude of reports concerning partial or complete third nerve palsies, especially as presenting symptoms with posterior communicating artery (PCoA) aneurysms, we present a patient with an unusual variation. CASE DESCRIPTION A 66-year-old woman presented with progressive right-sided headaches and diplopia and was found to have a partial, pupil-sparing third nerve palsy. A small right-sided PCoA aneurysm, nearly indistinguishable from an infundibulum, was identified on magnetic resonance angiography and subsequent digital subtraction angiography. The third nerve palsy improved before surgical repair of the aneurysm. RESULTS Microsurgical exploration revealed a small PCoA aneurysm, which was tethered to the third nerve by arachnoid adhesions. Adhesions were lysed and the aneurysm was repaired sparing the PCoA and its branches. The patients third nerve function recovered completely postoperatively. CONCLUSIONS Even a very small PCoA aneurysm may present with an improving, pupil-sparing partial third nerve palsy. Selection of patients for imaging studies should take this unusual variant into consideration. We describe the anatomy and potential mechanisms of this pupil-sparing third nerve palsy.

High-Frequency Stimulation of Dorsal Column Axons: Potential Underlying Mechanism of Paresthesia-Free Neuropathic Pain Relief.

Spinal cord stimulation (SCS) treats neuropathic pain through retrograde stimulation of dorsal column axons and their inhibitory effects on wide dynamic range (WDR) neurons. Typical SCS uses frequencies from 50–100 Hz. Newer stimulation paradigms use high‐frequency stimulation (HFS) up to 10 kHz and produce pain relief but without paresthesia. Our hypothesis is that HFS preferentially blocks larger diameter axons (12–15 µm) based on dynamics of ion channel gates and the electric potential gradient seen along the axon, resulting in inhibition of WDR cells without paresthesia.