We thank de Carvalho and Swash for their valuable comments on our study.1 In their prospective study of 10 patients with PMA with relatively short mean disease durations (maximum 14 months), they describe a follow-up of 12 months with variable disease progression and with development of respiratory involvement in 4 patients and death due to respiratory failure in 2.2 Axial-onset disease especially was more likely to progress to respiratory involvement, which can be explained by the adjacent location of anterior horn cells innervating axial and respiratory muscles. In our group of 32 patients with a mean follow-up of 6 years, only 1 patient had a bulbar onset with axial weakness and a progressive disease course with the development of respiratory involvement and upper motor neuron signs such that the diagnosis was changed to ALS. However, these 2 groups cannot be easily compared because of the differences in disease duration. In a previously published study, we described 37 patients with PMA3 with a median disease duration of 15 months, comparable with the study by de Carvalho and Swash.2 Although none of the 37 patients had a bulbar or axial onset, 10 had bulbar signs and symptoms at inclusion, and all died owing to respiratory failure during follow-up. The median survival duration after initial weakness was 56 months in the group, which is comparable with previous studies of ALS. The variable disease progression in groups of patients with relatively short disease duration can thus be explained by the heterogeneity of the groups, consisting of both PMA, having a relatively bad prognosis, and segmental forms with no or minimal progression.
Van den Berg-Vos RM. What Is Really New in Progressive Muscle Atrophy?—Reply. Arch Neurol. 2009;66(11):1427-1429. doi:10.1001/archneurol.2009.255