Muscular Dystrophy- prognostic indicators

[Marie Raven]

I’m finding that there are a number of tests and measures useful for predicting the cessation of ambulation or the onset of need for mechanical ventilation/ventilation assistance for DMD. However, I can’t find specific values for some of the tests. In the first practice exam it indicates that “The knee extension lag while sitting and the hip extension lag while prone are assessed to predict the cessation of independent walking. If the combined lag is greater than 90 degrees, the termination of independent ambulation will occur within a few months.” This was a new measure for me that I’d not heard of. I’ve seen specific references to the timed 4 step climbing test and 10 m walk-run test with specific cut offs in terms of the number of seconds the test takes the patient indicating loss of ambulation within different time periods. I’m also reading that the 6 minute walk test is correlated with loss of ambulation, but not seeing a cut-off or time frame related to this test, just that the MCID is 30 meters. How does that MCID impact judgment about loss of ambulation?

[Jessica Lewis]

Hi Marie!

Here is what I found for you…For the 6MWT, from what I understand, it’s not necessarily about the specific number of meters lost, it’s about the percentage the patient is below the predicted distance they should be able to walk. This threshold is 55% below the predicted distance (approximately 325 meters). Once children reach this threshold, a high percentage decline >10% over the subsequent year, quickly on their way to losing ambulation. Reaching this threshold value doesn’t necessarily help predict when a child will lose ambulation, but it is an indicator that they are on their way, likely within the next year or two.

The 30 meter MCID is helpful for drug research studies to help determine what change scores are important.

I also have a message out to an expert. If she says anything different, I’ll let you know!

McDonald CM, Henricson EK, Abresch RT, et al. The 6-minute walk test and other endpoints in Duchenne muscular dystrophy: longitudinal natural history observations over 48 weeks from a multicenter study. Muscle Nerve. 2013;48(3):343-356. doi:10.1002/mus.23902

[Jessica Lewis]

UPDATE from my expert friend who is a PI for DMD research:

She stated that a 6MWT less than 350 meters is an indication that the child will be losing ambulatory status within a year or so (assuming the child is old enough to be on the downturn…this is usually around 10 years old). If the child’s walk distance is below 275-250 meters, that would signal imminent loss. She also added that a walk >500 meters is really stellar for DMD 🙂

So, for the most part, similar to what McDonald et al. found.

[Author]

Posts