Seward Rutkove Laboratory
Our focus is on translational research into the development of novel diagnostics and therapeutics for the care of individuals with
neuromuscular disease. Our lab focuses on a wide range of disorders, affecting adults and children, including amyotrophic lateral sclerosis, neuropathies, muscular dystrophy, radiculopathy and spinal nerve compression syndromes, spinal muscular atrophy, and inflammatory myopathies. Much of our work involves the refinement of innovative bioengineering approaches to diagnosing and treating these disorders. However, we are also interested in studying mechanism of disease pathogenesis and potential therapeutics. Finally, we also have an abiding interest in clinical neurophysiological measures as well as novel indices of disease status.
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1. Electrical Impedance Myography (EIM)
A. Underlying concepts.
A major focus of the laboratory is the refinement of the technique of electrical impedance myography (EIM). Based on bioimpedance concepts, EIM involves the application and measurement of high-frequency, low-intensity electrical current via surface electrodes. The basic concepts underlying EIM are summarized in the figure below. Electrical current is applied via two outer surface electrodes (represented by the black sinusoid), generating a voltage measured by 2 the inner electrodes (the red sinusoid). The voltage that develops is proportional to the tissue resistance. The lipid bilayers that make up myocyte membranes are also capacitive in nature (i.e., they briefly store and then release charge) and therefore exhibit reactance (X), making the voltage sine wave out of phase with applied current wave. The reactance and resistance values are combined to obtain the phase angle (θ) via the relationship θ = arctan(X/R). The figure on the right shows an example of changes that might be observed in diseased muscle. Here, the presence of connective tissue, fat and reduced muscle mass substantially increase the measured resistance; muscle fiber atrophy and loss also results in a reduced reactance (i.e. the timing of voltage sinusoid is now only slightly shifted relative to the current). Thus, the phase angle, as well as the raw resistance and reactance values can all be used as measures of disease progression. As a disease progresses, reactance and phase angle decrease whereas resistance increases.
There are two additional important aspects to this mechanistic discussion. First, there is a very strong frequency dependence to the measurements since muscle, connective tissue and fat all have distinct electrical properties that are frequency-dependent. "
Thus, performing electrical impedance measurements across a range of frequencies can help to fully characterize the tissue. A second feature of impedance measurement is that of electrical anisotropy, the directional dependence of current flow. Electrical current flows more easily along muscle fibers than across them conferring a readily detectable anisotropy. The alteration in electrical anisotropy can also be used as a measure of disease severity within a disease state. Recent data obtained in spinal muscular atrophy patients, shown in the preliminary data section, confirms the potential importance of evaluating anisotropy as well.
B. Approaches for measurement.
For human measurement, we use several different approaches for performing EIM. Most of our early work utilized off-the-shelf bioimpedance systems that we reconfigured for use with a focus on localized areas of muscle. Although we continue to utilize these approaches in some of our ongoing clinical work, more recently in collaboration with Professor Joel Dawson's Laboratory at MIT, we have developed our own system for performing impedance measurements. The advantage of this system is that it allows for rapid multi-freqeuency measurements at multiple angles relative to the muscle fiber direction, thus allowing assessment of muscle anisotropy and the alterations in anisotropy in disease states. Further refinements to this system are currently ongoing.
For animal studies, we utilize several other impedance measuring systems. Most of these are focused on obtaining multi-frequency data from the gastrocnemius muscles of mice and rats, without an attempt to measure anisotropy. "
However, current work is expanding in this direction given the potentially informative data that anisotropic measurements may provide. "For examples of our measurement techniques in animals, please see the reference section. We also perform finite element modeling as a technique for assessing how disease-induced alterations affect the surface EIM measurements. Through such analyses, we ultimately will work backward such that we can identify how the surface recorded impedance data reflect the condition of the underlying muscle. In addition to our ongoing clinical work here, EIM is also being utilized as an outcome measure in the first North American stem cell study in ALS, funded by Neuralstem, Inc.
C. Examples of data
Our analytical methods depend very much on whether we are just looking at single frequency data over time or are interested in evaluating the multi-frequency spectrum of the data or evaluating the anisotropy. "
One early data set showing very promising results was that for identifying the progression of ALS. The figure shows an example of disease progression in a group of ALS patients over time. The ability to sensitively measure the progression of ALS is critical to being able to perform more rapid clinical trials in the disease. An ongoing multicenter trial further exploring the ALS application of EIM is now nearing completion
The multi-frequency data is more complex to analyze; however, the basic alteration in the impedance data is summarized neatly in the figure below which shows the impedance spectra (both resistance and reactance) recorded from the tibialis anterior muscle of 3 children: one normal, one with mild spinal muscular atrophy, and one with more severe spinal muscular atrophy. As can be seen, there is a major alteration in the impedance spectrum with disease severity.
Thus, the expectation is that alterations in the frequency dependence of impedance will offer even better sensitivity to disease progression than assessing single frequencies alone.
Analyzing the multi-frequency and multiangle data simultaneously is more challenging. However, the figure below shows an example of some of our early resistance data acquired with the probe shown above.
2. Peripheral Neuropathy Research
The laboratory is also interested in polyneuropathy pathogenesis and the application of clinical neurophysiological techniques for its assessment. We have focused our efforts on two of the most common forms of polyneuropathy: that due to diabetes and that due to chemotherapy exposure. "
The work on diabetic neuropathy has mainly focused on the interaction of temperature with the pathogenesis of polyneuropathy. We have identified a subtle but definite effect on long term exposure to cold and the exacerbation of polyneuropathy in diabetic animals. Recent work has also demonstrated impaired distal thermoregulation in patients with diabetic polyneuropathy, resulting in colder feet. Reduction in foot temperature can lead to a vicious cycle of impaired neuronal function causing worsened cooling and hence worsening polyneuropathy. Impairments in distal thermoregulation may also lead to increased pain. This work has been pursued in collaboration with Aris Veves, MD and Theophano Mitsa, PhD. Further studies in assessing the fluctuations in temperature are being pursued also with Ary Goldberger, MD and Madelena Costa, PhD, at the Margaret and H.A. Rey Institute for Nonlinear Dynamics in Medicine
More recently, we are utilizing the concepts of nerve excitability testing to further explore alterations in nerve function, this time focusing on chemotherapy-induced neuropathy, a very common cause of disability faced by cancer survivors. This research, being pursued in conjunction with Hiroyuki Nodera, MD, an expert in the field, explores the concepts of pursuing novel prophylactic strategies to protect the nerve prior to exposure of chemotherapeutic agents.
3. Additional projects
We are involved in a variety of other smaller/newer projects. These include:
A. Developing methodologies for applying quantitative ultrasound as novel biomarkers in neuromuscular disease assessment. Although ultrasound is mainly used as a diagnostic imaging technique, using US to assess neuromuscular progression is a very exciting, relatively unexplored area. "
Since ultrasound is painless and rapid to perform such analyses could offer exciting opportunities relevant to a variety of neuromuscular diseases. This work is being pursued in conjunction with Charles Sodini, PhD at MIT.
B. Micro-implants for assessing disease status. In collaboration with Professor Joel Dawson's Laboratory at MIT, we are also exploring and developing implantable recorders that can provide long-term physiologic data on patients, including distal temperature monitoring, movement, and eventually chemo-detection.
C. Amyotrophic lateral sclerosis therapeutics and diagnostics. We are also interested in pursuing novel therapeutic and diagnostic concepts in ALS. Current work includes improving approaches for assessing disease progression using standard neurophysiologic measures, such as motor unit number estimation. We are also assessing novel hormone-focused treatment strategies in this disease, in conjunction with the laboratory of Dr. Anthony Hollenberg at Beth Israel Deaconess Medical Center.
D. Application of electrical impedance tomography to neuromuscular disease assessment. Also an impedance-based technique, EIT offers a different perspective on muscle and the possibility of imaging muscle rapidly. This work is in collaboration with Andrea Borsic, PhD and Ryan Halter, PhD at Dartmouth Thayer School of Engineering.
E. Lumbosacral plexitis models. We have been pursuing a program of research to develop a novel model of lumbosacral plexitis, an inflammatory disorder affecting the nerves of the lower extremity.