Changes in Quality of Life in Parkinson's Disease: How Large Must They Be to Be Relevant?
BACKGROUND
Minimal clinically important difference (MCID) is the smallest change in an outcome, which a patient identifies as meaningful. Although the 2 most frequently applied Parkinson's disease (PD) "quality of life" questionnaires (the PDQ-39 and PDQ-8) provide encouragingly similar results, their MCID thresholds appear to be vastly different. Our aim was to calculate the MCID estimates for both PDQ-39 and PDQ-8 Summary Indices (PDQ-39-SI and PDQ-8-SI) by the utilization of both anchor- and distribution-based techniques.


METHODS
Nine hundred eighty-five paired investigations of 365 patients were included. Three different techniques were used simultaneously to calculate the MCID values.


RESULTS
First, we replicated the previously published results demonstrating how both PDQ-39-SI and PDQ-8-SI provide similar values and respond in a similar way to changes. Subsequently, we calculated the MCID thresholds. The most optimal estimates for MCID thresholds for PDQ-39-SI were -4.72 and +4.22 for detecting minimal clinically important improvement and worsening. For PDQ-8-SI, these estimates were -5.94 and +4.91 points for detecting minimal clinically important improvement and worsening respectively.


CONCLUSIONS
Our study is the first one that directly compared the MCID estimates for both PDQ-39-SI and PDQ-8-SI on a large pool of patients including all disease severity stages. These MICD estimates varied across PD severity.
Doctoral School of Clinical Neuroscience, University of Pécs, Pécs, Hungary.
Krisztina
K
Horváth
Zsuzsanna
Z
Aschermann
Márton
M
Kovács
Attila
A
Makkos
Márk
M
Harmat
József
J
Janszky
Sámuel
S
Komoly
Kázmér
K
Karádi
Norbert
N
Kovács
D000368:Aged; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D000071081:Minimal Clinically Important Difference; D010300:Parkinson Disease / Q000175:diagnosis / Q000523:psychology*; D011788:Quality of Life; D012372:ROC Curve; D015203:Reproducibility of Results; D012720:Severity of Illness Index; D011795:Surveys and Questionnaires
Minimal clinically important change; Minimal clinically important difference; Parkinson’s disease; Patient reported outcomes; Receiver operating characteristic curve