Validation of the French Translation of the Movement Disorder Society Non‐Motor Symptoms Scale (MDS‐NMS) in Parkinson's Disease

Abstract

Full text

The MDS‐Non‐Motor Symptoms Scale (MDS‐NMS) is a comprehensive tool to assess NMS in Parkinson's disease (PD), which represent a major source of disability and impact on quality of life throughout the disease course.1, 2 While validated in several languages,3, 4 a French version was lacking, limiting its use in French‐speaking populations worldwide. We followed the official Movement Disorder Society‐Clinical Outcome Assessment protocol to translate, adapt, and validate the French version, including forward–backward translation, expert review, and cognitive pretesting. Methodological details of the analyses are provided in Supplementary Material S1, including translation protocol, primary/secondary analysis and cognitive pretesting details.

A total of 303 PD patients were recruited from 10 expert centers within the NS‐Park French clinical research network. Inclusion criteria required a confirmed diagnosis of PD and high proficiency in French. Participants had a mean age of 62.3 years and mean disease duration of 8.2 years; most were in Hoehn & Yahr stage 2. Full demographic data are available in Supplementary Table S1.

Cognitive pretesting in 10 patients demonstrated the clarity and acceptability of the translated scale, with no item requiring rewording or removal. The scale was acceptable, culturally appropriate, and needed no major adaptation, allowing its approval as an “official working document” per MDS standards. This step ensured that the translation preserved both linguistic fidelity and clinical relevance, and could be implemented uniformly across clinical centers.

Confirmatory factor analysis (CFA) confirmed the structure of the original English version, with CFI values ≥0.90 for most subscales (Table 1). Domains with too few items—such as Apathy, Orthostatic Hypotension, Sexual, and Urinary—did not yield model fit indices due to statistical limitations. Exploratory factor analysis (EFA) revealed high item‐factor loadings (≥0.40), with dominant factors explaining substantial variance in key domains (eg, Depression: 57.2%, Cognition: 53%). Full EFA results and variance data are presented in Supplementary Table S2, and scree plots are shown in Supplementary Figure S1.

The MDS‐NMS covers 13 symptom domains and non‐motor fluctuations, enabling a detailed and multidimensional assessment of neuropsychiatric, autonomic, sleep‐related, sensory, gastrointestinal, and cognitive symptoms. This breadth is essential for understanding the full complexity of PD beyond motor features. Our findings align closely with prior validations in Portuguese and Spanish,3, 4 confirming the cross‐cultural robustness of its structure.

The French MDS‐NMS is particularly relevant for longitudinal studies, clinical trials, and real‐world evaluations of PD. It enables better characterization and follow‐up of NMS, which are often underrecognized and undertreated despite their burden. Its use may support more personalized care strategies and facilitate cross‐national research collaborations. Some domains—such as gastrointestinal and sleep‐wakefulness—showed more complex factor structures, as observed in other language validations, suggesting potential avenues for refinement. Future efforts may focus on validating a French patient‐reported version, as has been done for the English MDS‐NMS‐Q.5

In conclusion, the French MDS‐NMS is a valid, culturally adapted scale aligned with international standards. It represents a key step toward harmonizing the assessment of NMS in PD across language barriers and optimizing care for French‐speaking patients worldwide.

Author Roles

At the end of the manuscript, list the itemized contributions in number/letter format, as below. These should include but are not restricted to: (1) Research project: A. Conception, B. Organization, C. Execution; (2) Statistical Analysis: A. Design, B. Execution, C. Review and Critique; (3) Manuscript Preparation: A. Writing of the first draft, B. Review and Critique.

C.D.: 1C, 2C, 3A, 3B.

S.G.: 1C, 2C, 3A, 3B.

S.L.: 2A, 2B, 2C, 3B.

L.Y.: 2A, 2B, 2C.

C.G.G.: 1A, 1B, 2C, 3B.

G.T.S.: 1A, 1B, 2C, 3B.

P.M.M.: 1A, 1B, 2C, 3B.

M.M.K.: 1A, 1B, 2C, 3B.

T.A.M.: 1A, 1B, 2C, 3B.

A.S.F.: 1A, 1B, 2C, 3B.

M.H.S.T.: 1A, 1B, 2C, 3B.

R.B.: 1A, 1B, 2C, 3B.

C.L.: 1A, 1B, 2C, 3B.

C.G.S.: 1A, 1B, 2C, 3B.

T.W.: 1A, 1B, 1C, 2C, 3B.

O.C.: 1A, 1B, 1C, 2C, 3B.

D.M.: 1A, 1B, 1C, 2C, 3B.

L.D.: 1A, 1B, 1C, 2C, 3B.

C.G.: 1A, 1B, 1C, 2C, 3B.

M.C.: 1A, 1B, 1C, 2C, 3B.

C.T.: 1A, 1B, 1C, 2C, 3B.

C.L.: 1A, 1B, 1C, 2C, 3B.

M.T.: 1A, 1B, 1C, 2C, 3B.

G.D.: 1A, 1B, 1C, 2C, 3B.

P.R.: 1A, 1B, 1C, 2C, 3B.

C.T.: 1A, 1B, 1C, 2C, 3B.

S.D.: 1A, 1B, 1C, 2C, 3B.

A.S.: 1A, 1B, 1C, 2C, 3B.

I.B.: 1A, 1B, 1C, 2C, 3B.

S.S.: 1C, 2C, 3B.

J.C.C.: 1C, 2C, 3B.

F.K.: 1A, 1B, 2C, 3B.

M.F.: 1A, 1B, 1C, 2C, 3B.

O.R.: 1A, 1B, 1C, 2C, 3B.

Disclosures

Ethical Compliance Statement: According to the French ethic and regulatory law (public health code) retrospective studies based on the exploitation of usual care data do not require to be submitted at an ethics committee but they have to be declared or covered by reference methodology of the French National Commission for Informatics and Liberties (CNIL). The authors confirm that the approval of an institutional review board was not required for this work. All patients received written information about the study, and could express their opposition rights through the cohort website in accordance to EU General Protection Data Regulation rules (https://parkinsonnetwork/la-cohorte-ns-park) (https://parkinson.network/). A collection and computer processing of personal and medical date was implemented to analyze the results of the research. Toulouse University Hospital signed a commitment of compliance to the reference methodology MR‐004 of the French National Commission for Informatics and Liberties (CNIL). After evaluation and validation by the data protection officer and according to the General Data Protection Regulation*, this study completing all the criteria, it is register in the register of data study of the Toulouse University Hospital (number's register: RnIPH 2023‐39) and cover by the MR‐004 (CNIL number: 2206723 v 0). We confirm that we have read the Journal's position on issues involved in ethical publication and affirm that this work is consistent with those guidelines.

Funding Sources and Conflicts of Interest: No specific funding was received for this work. The authors declare that there are no conflicts of interest relevant to this work.

Financial Disclosures for the previous 12 months: CD received Honoraria to speak from Téva Santé and Expression Santé, consultancies for Téva Santé. GTS received consulting and advisory board honoraria from Alzheimer's Association, Critical Path Institute, International Parkinson and Movement Disorder Society, Huntington Study Group, Lilly USA, Michael J. Fox Foundation for Parkinson's Research, Neurocrine Biosciences, Inc., Octave Bioscience, Pfizer, Inc., Vima Therapeutics, Inc., WCG Clinical, Inc. He has received grants from Critical Path Institute, CHDI Management, Inc., International Parkinson and Movement Disorder Society, Michael J. Fox Foundation for Parkinson's Research, Ottawa Hospital Research Institute, University of California at San Diego, University of California at San Francisco. TAM received consulting and advisory board membership honoraria with Abbvie, International Parkinson and Movement Disorder Society, AbbVie, CHDI Foundation/Management, Merz, WAVE pharmaceutical, PTC therapeutics and Roche. He has research grants with EU Joint Program—Neurodegenerative Disease Research, uOBMRI, Roche, Ontario Research Fund, CIHR, Michael J. Fox Foundation for Parkinson's Research, Parkinson Canada, Parkinson Research Consortium and Brain Canada. He receives salary with University of Ottawa Medical Associates. RB received a travel grant from Lusofarmaco. Alvaro Sanchez‐Ferro received grants or contracts from MDS (eDiary project), and Instituto de Salud Carlos III (reference number P122/01177); consulting fees from AbbVie, Boston Scientific, Esteve, Orion Pharma, Prim; and Roche and payment or honoraria for lectures, presentations, speakers bureaus, manuscript writing, or educational events from AbbVie, Bayer, Esteve, MDS Society, EAN, Novartis, Monitor, Organon, Roche, SEN, Stada, Teva, and Zambon. Salary: Leuko Labs and Hospital 12 de Octubre. Royalties from Patents. Stock: Leuko Labs. MHST received salary—Rush University; Professional Societies: working group supported by the International Parkinson and Movement Disorder Society. CG‐S received consulting with honoraria: Instituto de Salud Carlos III. Grants: Community of Madrid Grant for Research Assistant. Funding to attend a scientific meeting: Esteve. CT has received honoraria or travel grants from AbbVie and Adelia. JCC has served in advisory boards for Alzprotect, Bayer, Ferrer, iRegene, Servier, UCB, Roche; and received grants from AXA and the ICM Foundation outside of this work. OR has acted as a scientific advisor for drug companies developing antiparkinsonian medications (Abbott, Abbvie, Acorda, Adamas, BIAL, Biogen, Boehringer‐Ingelheim, Cynapsus, GSK, Impax, Merck, Osmotica, Oxford‐Biomedica, Lundbeck, Novartis, Prexton, Servier, Sunovion, TEVA, UCB, Zambon). Margherita Fabbri received Honoraria to speak from AbbVie, ORKYN, and BIAL, consultancies from BIAL and LVL Medical; Grant from France Parkinson, HORIZON 2022 French Ministry of Health and MSA Coalition.

Supporting information

Figure S1. Scree plots for each domain of the MDS‐NMS, demonstrating the eigenvalue distribution across factors. The plots illustrate the distinct factor separations, with clear declines at the elbow points, confirming the number of meaningful factors retained for each domain. These visualizations support the robustness of the factor structure and align with theoretical expectations for domain‐specific dimensionality.

Data S1. Detailed Methodology of Analyses. Comprehensive description of the statistical procedures and analyses used for confirmatory and exploratory factor analyses of the French MDS‐NMS, including estimation methods, rotation strategy, fit indices, and rationale for sample size.

Table S1. Demographic data of the French Population. SD, standard deviation; PD, Parkinson's Disease; HY, Hoehn and Yahr.

Table S2. Factor loadings and percent variance explained by each factor in the French version of the NMS‐MDS Scale. Factor 1: The primary factor identified for each symptom domain; Symptoms: Specific symptoms assessed within each domain; Loading: The factor loading, indicating the correlation between each symptom and the underlying factor; Percent variance: The percentage of total variance in the symptoms explained by Factor 1 within each domain.