OBJECTIVE : There is an urgent need for reliable and universally
applicable outcome measures for children with mitochondrial
diseases. In this study, we aimed to adapt the currently available
Newcastle Paediatric Mitochondrial Disease Scale
(NPMDS) to the International Paediatric Mitochondrial
Disease Scale (IPMDS) during a Delphi-based process with
input from international collaborators, patients and caretakers,
as well as a pilot reliability study in eight patients.
Subsequently, we aimed to test the feasibility, construct validity
and reliability of the IPMDS in a multicentre study.
METHODS : A clinically, biochemically and genetically heterogeneous
group of 17 patients (age 1.6–16 years) from five different expert centres from four different continents were
evaluated in this study.
RESULTS : The feasibility of the IPMDS was good, as indicated
by a low number of missing items (4 %) and the positive
evaluation of patients, parents and users. Principal component
analysis of our small sample identified three factors, which
explained 57.9 % of the variance. Good construct validity
was found using hypothesis testing. The overall interrater reliability
was good [median intraclass correlation coefficient
for agreement between raters (ICCagreement) 0.85; range
CONCLUSION : In conclusion, we suggest using the IPMDS for
assessing natural history in children with mitochondrial diseases. These data should be used to further explore construct
validity of the IPMDS and to set age limits. In parallel,
responsiveness and the minimal clinically important difference
should be studied to facilitate sample size calculations
in future clinical trials.