Chronic Cortical Stimulation for Amyotropic Lateral Sclerosis: A Report of Four Consecutive Operated Cases after a 2-Year Follow-up: Technical Case Report

Brain Stimulation as a Therapeutic Tool in Amyotrophic Lateral Sclerosis: Current Status and Interaction With Mechanisms of Altered Cortical Excitability

In the last 20 years, several modalities of neuromodulation, mainly based on non-invasive brain stimulation (NIBS) techniques, have been tested as a non-pharmacological therapeutic approach to slow disease progression in amyotrophic lateral sclerosis (ALS). In both sporadic and familial ALS cases, neurophysiological studies point to motor cortical hyperexcitability as a possible priming factor in neurodegeneration, likely related to dysfunction of both excitatory and inhibitory mechanisms. A trans-synaptic anterograde mechanism of excitotoxicity is thus postulated, causing upper and lower motor neuron degeneration. Specifically, motor neuron hyperexcitability and hyperactivity are attributed to intrinsic cell abnormalities related to altered ion homeostasis and to impaired glutamate and gamma aminobutyric acid gamma-aminobutyric acid (GABA) signaling. Several neuropathological mechanisms support excitatory and synaptic dysfunction in ALS; additionally, hyperexcitability seems to drive DNA-binding protein 43-kDA (TDP-43) pathology, through the upregulation of unusual isoforms directly contributing to ASL pathophysiology. Corticospinal excitability can be suppressed or enhanced using NIBS techniques, namely, repetitive transcranial magnetic stimulation (rTMS) and transcranial direct current stimulation (tDCS), as well as invasive brain and spinal stimulation. Experimental evidence supports the hypothesis that the after-effects of NIBS are mediated by long-term potentiation (LTP)-/long-term depression (LTD)-like mechanisms of modulation of synaptic activity, with different biological and physiological mechanisms underlying the effects of tDCS and rTMS and, possibly, of different rTMS protocols. This potential has led to several small trials testing different stimulation interventions to antagonize excitotoxicity in ALS. Overall, these studies suggest a possible efficacy of neuromodulation in determining a slight reduction of disease progression, related to the type, duration, and frequency of treatment, but current evidence remains preliminary. Main limitations are the small number and heterogeneity of recruited patients, the limited "dosage" of brain stimulation that can be delivered in the hospital setting, the lack of a sufficient knowledge on the excitatory and inhibitory mechanisms targeted by specific stimulation interventions, and the persistent uncertainty on the key pathophysiological processes leading to motor neuron loss. The present review article provides an update on the state of the art of neuromodulation in ALS and a critical appraisal of the rationale for the application/optimization of brain stimulation interventions, in the light of their interaction with ALS pathophysiological mechanisms.

Quantitative SPECT/CT-Technique and Clinical Applications

The continuous development of SPECT over the past 50 years has led to improved image quality and increased diagnostic confidence. The most influential developments include the realization of hybrid SPECT/CT devices, as well as the implementation of attenuation correction and iterative image reconstruction techniques. These developments have led to a preference for SPECT/CT devices over SPECT-only systems and to the widespread adoption of the former, strengthening the role of SPECT/CT as the workhorse of Nuclear Medicine imaging. New trends in the ongoing development of SPECT/CT are diverse. For example, whole-body SPECT/CT images, consisting of acquisitions from multiple consecutive bed positions in the manner of PET/CT, are increasingly performed. Additionally, in recent years, some interesting approaches in detector technology have found their way into commercial products. For example, some SPECT cameras dedicated to specific organs employ semiconductor detectors made of cadmium telluride or cadmium zinc telluride, which have been shown to increase the obtainable image quality by offering a higher sensitivity and energy resolution. However, the advent of quantitative SPECT/CT which, like PET, can quantify the amount of tracer in terms of Bq/mL or as a standardized uptake value could be regarded as most important development. It is a major innovation that will lead to increased diagnostic accuracy and confidence, especially in longitudinal studies and in the monitoring of treatment response. The current work comprises two main aspects. At first, physical and technical fundamentals of SPECT image formation are described and necessary prerequisites of quantitative SPECT/CT are reviewed. Additionally, the typically achievable quantitative accuracy based on reports from the literature is given. Second, an extensive list of studies reporting on clinical applications of quantitative SPECT/CT is provided and reviewed.

Quantitative SPECT/CT

Conventional nuclear medical imaging uses radiopharmaceuticals labeled by single-photon emitters such as Tc-99m, I-123, or I-131 in vivo. Classical clinical examples are the study of bone metabolism by bone scintigraphy with the Tc-99m-labeled polyphosphonates or of iodine transport into the thyroid gland using Tc-99m-pertechnetate. With single-photon emission-computed tomography (SPECT), the distribution of these radiopharmaceuticals within the human body is three-dimensionally visualized. Contrary to positron emission tomography (PET), current SPECT technology does not allow the quantification of regional values of radioactivity tissue concentration as SPECT images are grossly compromised by artifacts caused by photon scatter and attenuation. With the advent of hybrid imaging systems combining a SPECT camera with an X-ray computerized (CT) scanner in one gantry, reliable corrections for these artifacts seem possible, allowing truly quantitative SPECT.

Absolute quantification in SPECT

Single-photon emission computed tomography (SPECT) allows the three-dimensional visualization of radioactivity within the human body and is widely used for clinical purposes. In SPECT, image quality is compromised by several factors including photon attenuation, photon scatter, the partial volume effect, and motion artefacts. These variables also confound the capacity of SPECT to quantify the concentration of radioactivity within given volumes of interest in absolute units, e.g. as kilobecquerels per cubic centimetre. In the last decade, considerable technical progress has been achieved in SPECT image reconstruction, involving, in particular, the development of iterative image reconstruction techniques. Furthermore, hybrid cameras integrating a SPECT camera with an X-ray CT scanner have become commercially available. These systems allow the acquisition of SPECT and CT datasets registered to each other with a high anatomical accuracy. First studies have shown that iterative SPECT image reconstruction techniques incorporating information from SPECT/CT image datasets greatly increase the accuracy of SPECT in quantifying radioactivity concentrations in phantoms and also in humans. This new potential of SPECT may improve not only diagnostic accuracy, but also dosimetry for internal radiotherapy.

Long-term motor cortex stimulation for amyotrophic lateral sclerosis

BACKGROUND

Motor cortex stimulation has been proposed for treatment of amyotrophic lateral sclerosis (ALS) and preliminary studies have reported a slight reduction of disease progression using both invasive and noninvasive repetitive stimulation of the motor cortex.

OBJECTIVE

The aim of this proof of principle study was to investigate the effects of motor cortex stimulation performed for a prolonged period (about 2 years) on ALS progression.

METHODS

Two patients were included in the study; the first patient was treated with monthly cycles of repetitive transcranial magnetic stimulation (rTMS) and the second one was treated with chronic epidural motor cortex stimulation. The rate of progression of the disease before and during treatment was compared.

RESULTS

The treatments were well tolerated by the patients. Both patients deteriorated during treatment; however, the patient treated with rTMS showed a slight reduction in deterioration rate.

CONCLUSIONS

Although we cannot be sure whether the effects observed in the patient treated with rTMS can be attributed to this form of stimulation, our study set the groundwork for possible future studies investigating the effects of rTMS, for a prolonged period, on a larger group of ALS patients.

Technological development and advances in single-photon emission computed tomography/computed tomography

Single-photon emission computed tomography/computed tomography (SPECT/CT) has emerged during the past decade as a means of correlating anatomical information from CT with functional information from SPECT. The integration of SPECT and CT in a single imaging device facilitates anatomical localization of the radiopharmaceutical to differentiate physiological uptake from that associated with disease and patient-specific attenuation correction to improve the visual quality and quantitative accuracy of the SPECT image. The first clinically available SPECT/CT systems performed emission-transmission imaging using a dual-headed SPECT camera and a low-power x-ray CT subsystem. Newer SPECT/CT systems are available with high-power CT subsystems suitable for detailed anatomical diagnosis, including CT coronary angiography and coronary calcification that can be correlated with myocardial perfusion measurements. The high-performance CT capabilities also offer the potential to improve compensation of partial volume errors for more accurate quantitation of radionuclide measurement of myocardial blood flow and other physiological processes and for radiation dosimetry for radionuclide therapy. In addition, new SPECT technologies are being developed that significantly improve the detection efficiency and spatial resolution for radionuclide imaging of small organs including the heart, brain, and breast, and therefore may provide new capabilities for SPECT/CT imaging in these important clinical applications.

Repetitive transcranial magnetic stimulation for ALS

Repetitive transcranial magnetic stimulation (rTMS) of brain can modulate cortical neurotransmission, a novel paradigm of repetitive stimulation termed continuous theta-burst stimulation (cTBS) produces a pronounced and prolonged suppression of motor cortex excitability. The aim of this preliminary study was to investigate whether cTBS of motor cortex could have any beneficial effect in patients with amyotrophic lateral sclerosis (ALS). We performed a double-blind, placebo-controlled trial. Twenty patients with definite ALS were randomly allocated to blinded active or placebo stimulation. Repetitive stimulation of the motor cortex was performed for five consecutive days every month for six consecutive months. The primary outcome was the rate of decline as evaluated with the ALS functional rating scale. The treatment was well tolerated by the patients. Fifteen patients (seven active and eight sham) completed the study and were included in the 6-months analysis. Both active and sham patients deteriorated during treatment, however, active patients showed a modest but significant slowing of the deterioration rate. Though we cannot be sure whether the effects observed can be attributed to cTBS, because of the restricted number of patients studied, further investigation on a larger group of ALS patients is warranted. The results of the pilot study might open up a new therapeutic perspective in ALS based on neuromodulation.