The neuromuscular disorders include a wide group of conditions ranging from relatively mild focal problems, such as carpal tunnel syndrome, to severe, generalized diseases, such as amyotrophic lateral sclerosis (ALS). Current methods for evaluating these disorders remain limited to a variety of tests and procedures that are either invasive or remarkably qualitative in nature. One newer technique, electrical impedance myography (EIM), offers the prospect of obtaining quantitative data on muscle condition painlessly and non-invasively. However, no commercial devices specifically tailored for EIM use exist, with nearly all previous EIM work relying upon off-the-shelf bioimpedance devices designed for whole-body rather than single-muscle assessment. In Phase 1 of this SBIR, Convergence Medical Devices, Inc (CMD) developed an initial prototype system to test proof-of-principle innovative concepts in circuit design and data acquisition to provide highly sensitive and accurate data at an extended frequency range (out to 10 MHz) and over multiple angles relative to the major muscle fiber direction. This work was followed by supplemental work that produced the first hand-held device with robust electronics capable of similar measurements with a detachable, interchangeable electrode array. In this 3-year Phase 2 SBIR, CMD proposes to further refine that technology so as to assist in disease diagnosis and for following disease progression, with a specific focus on amyotrophic lateral sclerosis. In Aim 1 of the proposed grant, testing of multiple electrode array designs will be performed on a group of normal subjects and those with ALS to determine which electrode array designs offer the greatest reproducibility and ability to discriminate healthy from diseased individuals. In Aim 2, the device and the 3 best array designs identified in Aim 1 will be tested in 30 ALS patients, 30 patients with syndromes mimicking ALS (e.g., polyradiculopathy and motor-predominant neuropathy), and 30 subjects with suspected/possible ALS to determine the single best array design for diagnosis and to determine its sensitivity and specificity. This study will take place at CMD and four external sites and will be managed by the Northeast ALS trials Consortium (NEALS), the premier organization for overseeing clinical trials in ALS. In Aim 3, the 30 suspected/possible ALS patients recruited in SA2 and 30 additional suspected/possible ALS patients will be assessed monthly using EIM and the 3 arrays identified in SA1. All subjects will also undergo standard measurements of disease progression including handheld dynamometry, ALS Functional Rating Scale, and spirometry. The best array design for assessing disease progression will be identified and compared to conventional markers of disease progression to determine EIM's sensitivity to disease status. Thus, at the conclusion of this research program, we anticipate having developed and vigorously tested an EIM device and associated electrode designs that together will serve as a powerful new diagnostic and monitoring tool for neuromuscular disease.