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Digital motor and cognitive variability as early markers of the prodromal Parkinson’s disease spectrum
Chohan H, Waters S, Pérez-Carbonell L, Leschziner G, Periñán M, Huxford B, Eriksson S, Bestwick J et al.. medRxiv, 2026-09-10
Topic: Brain imaging, connectivity and assessment
Background Individuals with isolated REM sleep behaviour disorder (iRBD) show motor and cognitive dysfunction prior to clinical α-synucleinopathy. Performance instability may represent an earlier marker of neurodegeneration but remains underexplored using digital tests. Objectives To assess baseline and longitudinal differences in motor and cognitive performance and examine performance variability in iRBD and related phenotypes. Methods Three PD-risk-stratified prodromal cohorts (normosmic probable RBD (pRBD), hyposmic pRBD and polysomnography-confirmed iRBD (PSG-iRBD)) were compared with healthy controls. Participants completed the BRadykinesia Akinesia Incoordination (BRAIN) test, Distal Finger Tapping (DFT) test, and Trail Making Test (TMT) remotely. Motor outcomes included kinesia score (KS), akinesia time (AT), and incoordination score (IS); cognitive outcomes included TMT-A/B reaction times and executive function. Baseline differences were analysed using age- and sex-adjusted logistic regression, longitudinal change using linear mixed-effects models, and variability using the mean of squared successive differences (MSSD) and heteroscedastic modelling. Results At baseline, PSG-iRBD participants showed greater motor and cognitive impairment than controls, hyposmic pRBD demonstrated intermediate deficits and normosmic pRBD participants showed milder but significant impairments. Linear mixed-effects models showed no change in motor trajectories across all groups, while executive function declined significantly in PSG-iRBD (p=0.001). However, variance modelling showed widespread variability. Cognitive variability was elevated in PSG-iRBD and hyposmic pRBD participants (MSSD p<0.035), and heteroscedastic modelling captured significant visit-specific motor instability across all prodromal cohorts on the BRAIN test (all p<0.02). Conclusions Performance variability precedes measurable linear decline across PD-risk stratified groups. Remote digital testing offers a scalable framework to capture this early instability.
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APA 7th
Chohan, H., Waters, S., Pérez-Carbonell, L., Leschziner, G., Periñán, M., Huxford, B., et al. (2026). Digital motor and cognitive variability as early markers of the prodromal Parkinson’s disease spectrum. medRxiv. https://doi.org/10.64898/2026.09.06.26358479
Vancouver
Chohan H, Waters S, Pérez-Carbonell L, Leschziner G, Periñán M, Huxford B, et al. Digital motor and cognitive variability as early markers of the prodromal Parkinson’s disease spectrum. medRxiv. 2026. doi:10.64898/2026.09.06.26358479.
BibTeX
@article{chohan2026-da109d97,
author = {Chohan, H. and Waters, S. and Pérez-Carbonell, L. and Leschziner, G. and Periñán, M. and Huxford, B. and Eriksson, S. and Bestwick, J. and others},
title = {{Digital motor and cognitive variability as early markers of the prodromal Parkinson’s disease spectrum}},
journal = {medRxiv},
year = {2026},
doi = {10.64898/2026.09.06.26358479},
url = {https://doi.org/10.64898/2026.09.06.26358479}
}
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Key findings
- Methods Three PD-risk-stratified prodromal cohorts (normosmic probable RBD (pRBD), hyposmic pRBD and polysomnography-confirmed iRBD (PSG-iRBD)) were compared with healthy controls.
- Results At baseline, PSG-iRBD participants showed greater motor and cognitive impairment than controls, hyposmic pRBD demonstrated intermediate deficits and normosmic pRBD participants showed milder but significant impairments.
- Linear mixed-effects models showed no change in motor trajectories across all groups, while executive function declined significantly in PSG-iRBD (p=0.001).
- Cognitive variability was elevated in PSG-iRBD and hyposmic pRBD participants (MSSD p<0.035), and heteroscedastic modelling captured significant visit-specific motor instability across all prodromal cohorts on the BRAIN test (all p<0.02).
Study details
- Study designlongitudinal study
- Evidence strengthModerate
How this study scored 16/100
Preprint — not yet peer-reviewed. It scored 39 on the same rubric, but non-peer-reviewed sources are capped at 16, so it shows as 16. Scored zero for sample size, effect reported, studied in people and randomised / blinded because the record does not state it. We have no data on times cited, citations per year, impact for its field and year, cited by studies here, still being cited, senior author's track record, institution's track record and multi-centre collaboration, so those were left out: it earned 24 of the 62 points we could judge it on, which is 39 out of 100.
| Component | Points | Why |
|---|---|---|
| Journal tier | 2 / 10 | Tier 4 — not a peer-reviewed journal (medRxiv) |
| Journal's citation record | 0 / 4 | Not a journal article, so the journal's record does not count |
| Study design | 7 / 12 | A longitudinal study following the same people over time |
| Strength of evidence | 3 / 5 | Rated “moderate” in our summary |
| Peer-review validation | 4 / 10 | Preprint — not yet peer-reviewed. Hosted on a preprint server. |
| How recent | 5 / 5 | 2026 — within 1 year(s) of the newest study here |
| Sample size | 0 / 4 | Participant count not stated — scores zero (not stated in the record — scored 0) |
| Effect reported | 0 / 3 | No effect size reported — scores zero (not stated in the record — scored 0) |
| Studied in people | 0 / 3 | Not stated whether this was studied in people — scores zero (not stated in the record — scored 0) |
| Randomised / blinded | 0 / 2 | No randomisation or blinding stated — scores zero (not stated in the record — scored 0) |
| Times cited | — / 7 | No citation count (not found in OpenAlex) — left out of this score |
| Citations per year | — / 5 | No citation count or no year — left out of this score |
| Impact for its field and year | — / 6 | No field-weighted citation impact (OpenAlex has none yet) — left out of this score |
| Cited by studies here | — / 6 | Not yet checked against this library's citation graph — left out of this score |
| Still being cited | — / 4 | No yearly citation counts — left out of this score |
| Senior author's track record | — / 4 | Senior author's record not available — left out of this score |
| Institution's track record | — / 3 | No institution listed in OpenAlex — left out of this score |
| Multi-centre collaboration | — / 3 | Institutions not listed — left out of this score |
| Indexed in PubMed | 1 / 2 | Not in PubMed, but has a DOI |
| Free to read | 2 / 2 | Free to read |
| Points | 24 / 62 | Scored on 12 of 20 parts. We have no data for the rest, so they are left out: 24 of the 62 points we could judge it on is 39 out of 100. |
| Total | 39 / 100 | Capped to 16 because this is not a peer-reviewed article. |
What each of these 20 components measures, and what this score is not →
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