TABLE 1.

Severity‐based subtypes

Citation	Sample characteristics, mean ± SD						Cluster method	Cluster variables	Imaging method	Description of clusters (% prevalence)	Neuroimaging results
	N	Age, years	Education, years	Global cognition	Gender, % female	Disease duration, years
Barvas et al. (2021)	65 PD	67.9 ± 7.5	10.8 ± 4.8	MoCA: 21.8 ± 2.8	35%	7.4 ± 5.3	Latent profile analysis	Attention: attentional matrices Memory: RAVLT (delayed), ROCF (delayed) Executive: phonemic fluency, Stroop (errors & time), social cognition assessment, Ekman 60‐faces test Language: semantic fluency, object picture naming, action verb picture naming Visuospatial: JLO	NA	Cluster A (22%): intact cognition Cluster B (54%): intermediate cognition Cluster C (25%): cognitively impaired, particularly in executive function, naming, visuospatial function	NA
Dujardin et al. (2013)	489 PD, 69 PDD	63.4 ± 9.2	11.2 ± 3.3	MMSE: 27.1 ± 2.5	40%	8.2 ± 6.4	k‐means cluster analysis	Global efficiency: MMSE Attention/working memory: digit span (forward and backward) Verbal episodic memory: Grober and Buschke SRT or RAVLT (immediate & delayed) Executive: Stroop (interference & errors), TMT (B/A), phonemic and semantic fluency	NA	Cognitively intact patients (19%) Patients without cognitive deficits but with slight mental slowing (41%) Patients with slightly impaired overall cognitive efficiency and deficits in all cognitive domains except recognition memory (13%) Patients with severe mental slowing, impaired overall cognitive efficiency, and severe cognitive impairment in all domains (24%) Patients with very severe impairment in all cognitive domains (3%)	NA
								Measures specific to Maastricht Site Verbal episodic memory: RAVLT (immediate & delayed) Processing speed: WAIS symbol substitution test Visuospatial: visual and object spatial perception test
								Measures specific to Lille site Verbal episodic memory: Buschke SRT (immediate & delayed) Processing speed: SDMT Visuospatial: construction subscale of MDRS, MMSE pentagons
Dujardin et al. (2015)	156 PD	67 ± 7	11.4 ± 2.9	MMSE: 26.5 ± 2.5	30%	9.0 ± 5.4	k‐means cluster analysis	Global efficiency: MMSE, MDRS Attention/working memory: digit span (forward & backward), SDMT Executive: TMT (B/A), Stroop (interference & errors), phonemic fluency (single & alternating) Verbal episodic memory: HVLT‐R (learn1, immediate, delayed, recognition, intrusions) Language: BNT, semantic fluency Visuospatial: JLO	NA	Cognitively intact patients with high level of performance in all cognitive domains (26%) Cognitively intact patients with slightly slower performance than those in Cluster 1 (27%) Patients with deficits in all domains compared to Cluster 1 (37%) Patients with severe deficits in all cognitive domains compared to Cluster 1 (3%) Patients with severe deficits in all cognitive domains, no observable difference from Cluster 4 (7%)	NA
Hassan et al. (2017), using Dujardin et al. (2015) clusters	124 PD	67.0 ± 7.2	11.4 ± 3.2	MMSE: 26.6 ± 2.4	30%	9.2 ± 5.8			EEG: dense‐EEG source connectivity	See Dujardin et al. (2015) Cognitively intact (50%) Mild cognitive deficits (37%) Severe cognitive deficits (12%)	Disruptions in functional connectivity in the alpha 1 & 2, beta, and gamma frequency bands, with Group 1 > Group 2 > Group 3 in power spectral density. In the delta and theta frequency bands, power spectral density increased with cognitive impairment (Group 1 < Group 2 < Group 3). Functional alterations in frontotemporal connectivity observed between Group 1 and Group 2, and functional alterations in frontoparietal and frontocentral connectivity observed in Group 3
Lopes et al. (2017), using Dujardin et al. (2015) clusters	119 PD	65.3 ± 7.2	48.0 ± 3.3	MMSE: 27 ± 2.2	32%	8.7 ± 5.9			3‐T rs‐fMRI: graph theory and network‐based statistic	See: Dujardin et al. (2015) Cognitively intact (26%) Slight mental slowing (27%) Mild to moderate deficits (37%) Severe deficits (10%)	Functional segregation of the brain decreased with greater cognitive deficit (Group 1 > Group 2 > Group 3 > Group 4). Group 1 & Group 2 demonstrated greater hub connections in the associative frontal, temporal, and occipital areas as well as limbic, sensorimotor, and insular areas. Group 3 demonstrated greater hub connections than Group 4 in associative frontal, temporal, occipital, limbic, primary sensorimotor, and cingulate areas
Wolters et al. (2020), using Dujardin et al. (2015) clusters	124 PD	66.1 ± 7.0	12.0 ± 3.3	MMSE: 27.3 ± 2.1	31%	8.8 ± 5.4	3‐T MRI: Voxel‐ and vertex‐based morphometry	Reduced grey matter in left medial temporal pole in Group 4 compared to Group 1. Group 4 also showed reduced cortical thickness compared to Group 1 in the right inferior temporal gyrus. Reduced cortical folding in Group 4 compared to Group 1 in right temporal regions. No difference in white matter lesions across groups
Kenney et al. (2022)	494 PD	64.7 ± 9.0	15.0 ± 2.8	DRS‐2: 137.0 ± 4.5	28%	9.6 ± 5.3	Hierarchical & k‐means cluster analysis	Composite scores used for each domain Executive: Stroop (interference), TMT (B), phonemic fluency Verbal memory: HVLT‐R (delayed); WMS‐III logical memory (delayed) Language: BNT, semantic fluency Visuospatial: JLO, facial recognition test Attention/working memory: digit span (forward and backward)	NA	Cognitively average (31%): above average performance across all domains Low executive function (46%): below average performance across all domains, particularly in executive and memory composites Prominent executive/memory impairment (23%): impaired performance across all but visuospatial and attention composites	NA
McKinlay et al. (2009)	40 PD	66.5 ± 6.5	13.6 ± 1.0	MMSE: 28.5 ± 1.2	NR	6.5 ± 4.9	k‐means cluster analysis	Executive: phonemic and sematic fluency, clock drawing, key search, zoo map, Stroop (interference) Problem solving: card sorting, matrix reasoning, stockings of Cambridge, tower test Attention/working memory: digits span (forward & backward), LNS, reading span, spatial span Processing speed: Stroop (word & colour naming) Memory: logical memory (immediate & delayed), paired associates (immediate & delayed), auditory recall index Visuospatial: JLO, clock copying	NA	PD‐NCI (48%): no or minimal impairment PD‐UCI (22%): a variable or uncertain pattern of mild to severe impairments PD‐MCI (30%): severe impairment across most cognitive domains	NA
Souza et al. (2016)	40 PDD, 39 PD‐MCI, and 21 PD‐NC	61.3 ± NA	4.5 ± NA	MMSE: 24.3 ± NA	42%	8.2 ± NA	Hierarchical & k‐means cluster analysis	MMSE, clock drawing, digit span (forward & backward), CERAD word list (immediate, delayed, recognition), FAB, and semantic fluency	NA	Cluster 1 (40%): above average performance across all cognitive domains Cluster 2 (45%): average performance across all cognitive domains Cluster 3 (15%): below‐average performance across all cognitive domains	NA

Abbreviations: BNT, Boston Naming Test; CERAD, Consortium to Establish a Registry for Alzheimer's Disease; DRS‐2, Dementia Rating Scale 2; EEG, electroencephalography; FAB, Frontal Assessment Battery; HVLT‐R, Hopkin's Verbal Learning Test Revised; JLO, Judgment of Line Orientation; LNS, Letter Number Sequencing; MDRS, Mattis Dementia Rating Scale; MMSE, Mini‐Mental State Examination; MoCA, Montreal Cognitive Assessment; NA, not applicable; NR, Not reported; PD, Parkinson disease; PDD, PD dementia; PD‐MCI, PD with mild cognitive impairment; PD‐NC/PD‐NCI, PD with normal cognition; PD‐UCI, PD with uncertain cognition; RAVLT, Rey Auditory Verbal Learning Test; ROCF, Rey–Osterrieth Complex Figure; rs‐fMRI, resting‐state functional magnetic resonance imaging; SDMT, Symbol Digit Modality Test; SRT, Selective Reminding Test; TMT, Trail Making Test; WMS, Weschler Memory Scale.