Patient reported outcome instruments, which include Pompe Disease Symptom Scale (PDSS) and Pompe Disease Impact Scale (PDIS), appear to be reliable measures of the severity of symptoms and functional compromise in patients with late-onset Pompe disease (PD), according to a recently published study published in Neurology Clinical Practice.

Due to the difficulty in accurately characterizing and quantifying the severity of PD symptoms and their impact on daily life activities, researchers developed 2 patient-reported outcome instruments, namely the PDIS and PDSS, the authors noted.

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“The PDSS and PDIS are self-administered questionnaires specifically designed to capture, respectively, symptoms and impacts of LOPD on individuals 18 years and older,” the study team wrote.

The PDSS consists of an 11-point numerical scale for 12 items focusing specifically on late-onset PD symptoms such as dyspnea, fatigue, muscle pain, muscle weakness, and morning headache, among others. The PDIS, on the other hand, focuses on assessing symptom impact with items such as depression, anxiety, worry, rising from a sitting position, and the ability to climb stairs.

Mood items in the PDIS scale are measured through a numeric scale. In contrast, activity items, such as the ability to climb stairs, are measured through questions such as whether the activity was performed in the last 24 hours and the task’s difficulty; each question has its own numerical scale.

Both instruments were used to assess alfa the efficacy of alglucosidase in a randomized, double-blind trial called the COMET trial. Patients answered both instruments every 14 days at baseline and then 2 weeks before quarterly visits for 1 year. The trial included 100 participants. 

Statistical analysis revealed sufficient correlation within item scores of both instruments to allow the identification of a scale in both cases. However, the strong correlation between 2 item pairs in the PDSS scale suggested a redundancy of items.

The correlation between the results of both items and the criterion measured, combined with the correlation between pulmonary and motor function measures, supported the reliability and accuracy of both scales. 

“The PDSS and PDIS are reliable and valid measures that can be used to evaluate important LOPD-specific symptoms and impacts on patients in observational research and clinical trials and to monitor disease progression in clinical practice,” the authors concluded.


Dimachkie MM, Kishnani PS, Ivanescu C, et al. Measurement properties of 2 novel pros, the Pompe disease symptom scale and Pompe Disease Impact Scale, in the comet study. Neurol Clin. Published online August, 8, 2023. doi:10.1212/cpj.0000000000200181