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Outcome Measures in Clinical Trials

“Outcome measures” are the tools we use to try to measure if a new treatment is effective. Outcome measures for clinical trial need to be reliable and sensitive to change. For SMA, we are considering several different outcome measures, each having some advantages and limitations

Assessing muscle strength can be difficult in children, because the results depend on the patient’s effort. Also, the standard method of manual strength testing does not allow to grade small differences. Therefore, we are testing a device called a hand-held dynamometer. Using a dynamometer is easy and comfortable and allows for measuring small changes over a continuous range. Muscle strength, which can remain stable over long periods of time in childhood SMA, may not predict the child’s functional status.

Motor function testing is conducted by physical and occupational therapists, where they observe the child perform simple movements for about 30 minutes and score these in a standardized fashion. Several different scales are available, depending on the age and developmental status of the child. Examples of these include the Gross Motor Function Scale (GMFM), the Hammersmith SMA Functional Motor Scale (H-SMA-FMS), the Test of Infant Motor Performance (TIMP), and the Children’s’ Hospital of Philadelphia (CHOP) Test of Strength in SMA (CHOP Test).

A child’s total muscle mass can be measured using DEXA scanning. This is the same x-ray machine used to measure bone density, and is a painless test which usually lasts 15 minutes.

A breathing test can be used in children who can cooperate with the test, typically those over 5 years of age. They simply blow into a tube that measures their breathing function.

Motor Unit Number Estimation (MUNE) is a non-invasive test that measures the number of functional motor units using electrophysiological techniques. During this 30 minute test, brief low intensity stimulation is applied to the wrist and a response is recorded. MUNE’s are increasingly used in SMA and offer a measure directly related to the pathophysiology of the disease.

Quality of life questionnaires for children with SMA and their parents take 10 minutes to complete and provide information about each child and family’s perceived quality of life.