In this case-control study, participants were recruited from the Neurology Clinic at Skåne University Hospital, Sweden, as part of the prospective and longitudinal Swedish BioFINDER study (
www.biofinder.se) [
12]. As of November 2016, 229 individuals had been included in the Parkinson sub-study of BioFINDER, of which 67 did not perform DKI at baseline, 39 did not perform DKI during follow-up, and 8 cases did not pass QC (Online Resource
1). Consequently, we included 76 patients with PD and 38 healthy controls. For the present work, 76 subjects were included with a clinical diagnosis of probable PD. The diagnosis was made by neurologists trained in movement disorder diagnostics according to the National Institute of Neurological Disorders and Stroke (NINDS) criteria of PD [
10]. Neurologically healthy controls (HC), who did not have any objective cognitive or parkinsonian symptoms, were also recruited (
n = 38). All 114 subjects had clinical assessments and were scanned on two occasions on average 25.3 months apart, with a standard deviation of 4.3 months. Motor function and disease stage were evaluated using, e.g., Unified Parkinson’s disease rating scale motor part (UPDRS-III) [
7] and Hoehn and Yahr staging scale (H&Y) [
14]. The total score from the motor section of the UPDRS III was broken down into subscales for bradykinesia, rigidity, tremor, gait posture [
32]. Cognitive assessments were conducted by trained physicians using a Mini Mental State Examinations (MMSE) [
9]. To ensure standardization, assessments were conducted during patients “on” medication state, or fully responding to their PD medications (in the “on” state). The daily
l-dopa equivalent dose (LEDD) was calculated (Table
1) [
39]. At the time of testing, none of the patients exhibited any dyskinesia, dystonia, or other signs of involuntary movement.
Table 1
Subject characteristic
Age, years | 66.4 (8.1) | – | 65.0 (10.8) | – | .801 | – | – |
Sex (male/female) | 16:22 | – | 52:24 | – | .009 | – | – |
dMRI interval, month | – | 25.9 (2.3) | – | 25.3 (4.3) | .414 | – | – |
Disease duration, years | – | – | 5.5 (3.6) | 7.5 (3.6) | – | < .001 | – |
Bradykinesia | 0 (.0) | 0 (.0) | .7 (0.7) | .8 (.9) | < .001 | .360 | .360 |
Rigidity | .5 (.9) | .1 (.4) | 1.8 (2.5) | 1.9 (2.5) | < .001 | .383 | .293 |
Tremor | .0 (.3) | .1 (.4) | 3.8 (3.3) | 3.1 (3.1) | < .001 | .256 | .221 |
Gait/posture | .0 (.2) | .0 (.2) | .6 (1.0) | .8 (1.1) | < .001 | .313 | .313 |
Hoehn and Yahr stage | – | – | 1.8 (.6) | 2.0 (.9) | – | .237 | – |
UPDRS motor, score | 1.4 (2.5) | 1.7 (2.2) | 12.5 (8.6) | 14.0 (10.3) | < .001 | .215 | .347 |
MMSE, score | 28.2 (1.6) | 29.0 (1.2) | 29.2 (4.5) | 29.3 (4.7) | .390 | .006 | .024 |
LEDDTOTAL, mg | – | – | 527.4 (374.9) | 705.8 (350.6) | – | < .001 | – |