Dear colleague,

The International Paediatric Mitochondrial Disease Scale (IPMDS), a multi-dimensional scale rating clinically relevant aspects of mitochondrial disease in children, was developed during a Delphi-based process by an international expert team in close dialogue with patients and their parents. Designing a scale for general mitochondrial disease severity is challenging because of the wide variability in symptoms and (dis)abilities seen in children with mitochondrial disease. This complexity is reflected in the high number of items included in the IPMDS and the breath of the items reflecting the multi-systemic nature of the disease. Critically evaluating the psychometric properties in seventeen children in five international expert centres, we found good feasibility and an acceptable construct validity and reliability.

In this paper, and on the right side of this page, you can find the first report on the rational for the development of the IPMDS, including a first impression of the feasibility, reliability and validity of the current scale. Using the anonymously uploaded data from international collaborators, as well as more detailed studies on the psychometric properties in larger and more heterogeneous populations with a larger age-range, we aim to optimize the scale further in the coming years. Examples of future research questions include: is the inter-rater reliability of Domain 2 acceptable after optimizing the instructions in the manual; what is the minimal clinically important difference, and what is the influence of normal development and growth on the reliability and construct validity of the IPMDS, including the possible requirement of age-specific scales.

Here, you find the IPMDS scoring sheet as well as the manual and the instructional video of the IPMDS.

Since – also for this rare disease – the power is in the numbers, we kindly ask you to upload the completed IPMDS (anonymously). Please also include your comments on the IPMDS, especially in young children. The data will be used to further develop the IPMDS. When it comes to publication of these results, your contribution will be granted with co-authorship depending on the number of IPMDS scoring sheets uploaded.

Thank you very much in advance for your contribution.

Sincerely, on behalf of the IPMDS-working group,

Jan Smeitink and Saskia Koene