Six-Minute Walk Distance Is a Useful Outcome Measure to Detect Motor Decline in Treated Late-Onset Pompe Disease Patients.

Late-onset Pompe disease (LOPD) is a rare, progressive disorder characterized by limb-girdle muscle weakness and/or respiratory insufficiency, caused by acid alpha-glucosidase () gene mutations and treated with enzyme replacement therapy. We studied isometric muscle strength in eight muscle groups bilaterally using a Biodex dynamometer, as well as the Medical Research Council sum score (MRC-SS), hand grip strength, 6 min walk distance (6MWD), 10 m walk test (10MWT) and timed up-and-go test (TUG) in 12 adult, ambulatory, treated LOPD patients and 12 age-/gender-matched healthy controls, every 6 months for 2 years. The mean isometric muscle strength showed a significant decline in right and left knee extensors at 12 months in controls ( < 0.014; < 0.016), at 18 months in patients ( < 0.010; < 0.007) and controls (only right side, < 0.030) and at 24 months in both groups ( < 0.035). The mean 6MWD in patients significantly decreased after 24 months, from 451.9 m to 368.1 m ( < 0.003), whereas in controls, the mean 6MWD significantly increased after 6 months ( < 0.045) and 18 months ( < 0.020) (at 24 months = 0.054). In patients and controls, the MRC-SS, hand grip test, 10MWT and TUG did not show significant changes ( > 0.05). We conclude that the 6MWD is a useful outcome measure to detect motor decline in treated LOPD patients.