Objective: To investigate the convergent and discriminative validity of a patient-reported FMCS in people with typical PD (PwP).

Background: Although a patient-reported instrument is less costly and invasive than the administration of physical performance tests, no current established instrument assesses functional mobility through patient reports [1] .

Method: We developed the FMCS by allocating the items of the subscales Mobility and Activities of Daily Living of the validated and widely applied Parkinson’s Disease Questionnaire PDQ-39 [2] to the different characteristics of functional mobility according to the definition of Bouca et al. [3]. After summing up the items the FMCS score was transformed to a 0 – 100 scale and inverted by subtracting the individual score from the maximum score to enhance the interpretation of the results, i.e. a high score corresponds to a good functional mobility. Next, we assessed among other things the validity using the Timed Up and Go (TUG) [4] for convergent validity, and patient-reported (MDS-UPDRS II) compared to clinician-assessed (MDS-UPDRS III) motor symptoms [5] for discriminant validity.
All 246 PwP participating in the Luxembourg Parkinson’s study [6] and having completed a TUG in the past year were included in the cross-sectional analyses. Convergent validity was assessed by Spearman correlations, while a multiple regression followed by a t-Test was applied to test the standardized regression coefficients for differences to assess discriminant validity.

Results: 177 / 246 (72.0%) PwP were male. Mean age was 67.3±10.1, mean H&Y stage was 2.2±0.5, mean MDS-UPDRS II was 11.8±7.5, and mean MDS-UPDRS III was 32.5±13.4. Tests for convergent and discriminative validity led to preliminary results i.e. Spearman correlation coefficients (rs) ranging from -0.41 to -0.79 (p < 0.001). Hence, analyses of discriminant validity suggest sufficient ability of FMCS to, in line with our intention, significantly discriminate (p < 0.001) between patient-reported and clinician-assessed motor symptoms: FMCS was more strongly associated with patient-reported MDS-UPDRS II (rs=-0.79) than with clinician-reported MDS-UPDRS III (rs=-0.32).

Conclusion: The FMCS is a valid composite score to assess functional mobility through patient reports in people with PD. Further research including the validation of the FMCS in independent PD cohorts is required.

References: [1] Bouca-Machado R, Duarte GS, Patriarca M, et al. Measurement Instruments to Assess Functional Mobility in Parkinson’s Disease: A Systematic Review. Mov Disord Clin Pract 2020;7(2):129-139.
[2] Peto V, Fitzpatrick R, Jenkinson C. Self-reported health status and access to health services in a community sample with Parkinson’s disease. Disabil Rehabil 1997;19(3):97-103.
[3] Bouca-Machado, R., Maetzler, W., & Ferreira, J. J. (2018). What is Functional Mobility Applied to Parkinson’s Disease? J Parkinsons Dis, 8(1), 121-130. doi:10.3233/JPD-171233
[4] Podsiadlo D, Richardson S. The timed “Up & Go”: a test of basic functional mobility for frail elderly persons. J Am Geriatr Soc 1991;39(2):142-148.
[5] Goetz CG, Tilley BC, Shaftman SR, et al. Movement Disorder Society-sponsored revision of the Unified Parkinson’s Disease Rating Scale (MDS-UPDRS): scale presentation and clinimetric testing results. Mov Disord 2008;23(15):2129-2170.
[6] Hipp G, Vaillant M, Diederich NJ, et al. The Luxembourg Parkinson’s Study: A Comprehensive Approach for Stratification and Early Diagnosis. Front Aging Neurosci 2018;10:326.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/validation-of-a-patient-reported-functional-mobility-composite-score-fmcs-in-people-with-typical-parkinsons-disease/