B. Background and Significance ALS is a quickly progressive disease that results in skeletal muscle weakness, including ventilatory weakness, which is the ultimate cause of death for the vast majority of patients with ALS. Median survival from diagnosis is less than 3 years. There is only one drug approved to treat ALS, riluzole, and its effects to limit the progression of the illness are slight (6). Current study designs often use a primary endpoint of either death from ALS or initiation of long-term mechanical ventilation (LTMV). There are other tools to assess progression, which can include a questionnaire called the ALS functional rating scale (ALS-FRS), a direct measurement of strength, or an electromyography technique called motor unit number estimate (MUNE). Each has potential drawbacks, which include potential lack of objectivity in questionnaire and variable effort when assessing direct strength measurements. There has also been work to correlate magnetic resonance spectroscopy findings to progression in ALS, with some positive results (3). However, this technology is expensive, time consuming, and not widely available. Muscle ultrasound may be sensitive enough to quantitatively detect changes in muscle thickness (4), which may serve as an objective tool to measure disease progression, for the purpose of clinical trials. Muscle echointensity (EI) is also abnormal in ALS (2, 4), although this assessment is less reliable among different observers and ultrasound settings, resulting in less diagnostic precision. Normal values for muscle thickness and echointensity are available, with norms varying by age and weight (5). Muscle ultrasound is readily available, noninvasive, inexpensive, and could be used in the context of a clinical examination. Muscle ultrasound is painless and can be completed in a few minutes.