Muscle Ultrasound: A New Tool for Measuring Progression in ALS

Protocol for the Study - Muscle Ultrasound: A New Tool for Measuring Progression in ALS

A. Specific Aims The authors propose to study the change in muscle mass over time in patients with ALS. Muscle atrophy is a very common feature of the disease, and in clinical experience correlates with progressing weakness. As such, it is a qualitative marker of disease progress, although this lacks a quantitative marker. Muscle ultrasound is a safe, noninvasive, and rapid method of measuring muscle volume or thickness (1). Recently Arts, et al published an assessment of muscle ultrasound, specifically including reduced muscle depth and increased ultrasound echogenicity (2). We believe determining quantitatively the rate of progression of muscle mass in a group of patients with ALS will lead to a clinically useful tool to serve as a marker of disease progression, which may be useful in clinical trials for new therapies for this disease.

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.

C. Preliminary Studies/Progress Report As this is a pilot study, there is no preliminary data using muscle ultrasound longitudinally in patients with ALS. The study by Arts et al used muscle ultrasound to assist in the ALS diagnosis, but to our knowledge, muscle ultrasound has not been used to detect longitudinal changes in the illness. This study will help in the development of future studies testing pharmacologic agents in ALS, by providing muscle ultrasound as a validated endpoint in the progression of ALS.

D. Research Design and Methods Ten patients will be recruited to participate, and will have serial muscle ultrasound examinations every three months, at regularly scheduled clinic appointments in the Vanderbilt ALS clinic. Muscles examined will include forearm flexors, biceps, and tibialis anterior. The thickness of each muscle will be measured at standard sites for these muscles, in addition to the echogenicity as measured by a grayscale histogram representation. The rate of loss of ultrasound-measured muscle thickness will be assessed over time. Our hypothesis is that there will be significant loss of muscle thickness over time, which will correlate with disease severity. As different patients have different rates of deterioration, there will likely be significant differences in the rate of muscle volume loss from patient to patient. A secondary endpoint will be an increase over time in muscle echogenicity. Patients will complete the ALS Functional Rating Scale (ALSFRS-R), a 12 item subjective scale that assesses several motor functions, including function of speech, swallowing, respiration, and activities of daily living. Grip strength will be measured by hand grip dynamometry, using the best result from 3 attempts in each limb. Secondary analyses will also be conducted to correlate the decrease in ultrasound-measure muscle depth with the ALS Functional-Rating Scale, and with measures from hand grip dynamometry.