ObjectiveTo determine the effects of 10 years of enzyme replacement therapy (ERT) in adult patients with Pompe disease, focusing on individual variability in treatment response. MethodsIn this prospective, multicenter cohort study, we studied 30 patients from the Netherlands and France who had started ERT during the only randomized placebo-controlled clinical trial with ERT in late-onset Pompe disease (NCT00158600) or its extension (NCT00455195) in 2005 to 2008. Main outcomes were walking ability (6-minute walk test [6MWT]), muscle strength (manual muscle testing using Medical Research Council [MRC] grading), and pulmonary function (forced vital capacity [FVC] in the upright and supine positions), assessed at 3-to 6-month intervals before and after the start of ERT. Data were analyzed with linear mixedeffects models for repeated measurements. ResultsMedian follow-up duration on ERT was 9.8 years (interquartile range [IQR] 8.3-10.2 years). At the group level, baseline 6MWT was 49% of predicted (IQR 41%-60%) and had deteriorated by 22.2 percentage points (pp) at the 10-year treatment point (p < 0.001). Baseline FVC upright was 54% of predicted (IQR 47%-68%) and decreased by 11 pp over 10 years (p < 0.001). Effects of ERT on MRC sum score and FVC supine were similar. At the individual level, 93% of patients had initial benefit of ERT. Depending on the outcome measured, 35% to 63% of patients had a secondary decline after ≈3 to 5 years. Still, at 10 years of ERT, 52% had equal or better 6MWT and/or FVC upright compared to baseline. ConclusionsThe majority of patients with Pompe disease benefit from long-term ERT, but many patients experience some secondary decline after ≈3 to 5 years. Individual variation, however, is considerable.Glossary ERT = enzyme replacement therapy; FVC = forced vital capacity; IQR = interquartile range; LOTS = Late-Onset Treatment Study; MEP = maximal expiratory pressure; MIP = maximal inspiratory pressure; MRC = Medical Research Council; M6P = mannose-6-phosphate; pp = percentage points; QMT = quantitative muscle testing; 6MWT = 6-minute walk test.

Our results support a change of practice wherein a lumbar puncture can be withheld in patients with a head CT scan performed <6 hours after headache onset and reported negative for the presence of SAH by a staff radiologist in the described nonacademic setting.