Parkinsonian Hand or Clinician's Eye? Finger Tap Bradykinesia Interrater Reliability for 21 Movement Disorder Experts

Abstract

Background: Bradykinesia is considered the fundamental motor feature of Parkinson's disease (PD). It is central to diagnosis, monitoring, and research outcomes. However, as a clinical sign determined purely by visual judgement, the reliability of humans to detect and measure bradykinesia remains unclear.

Objective: To establish interrater reliability for expert neurologists assessing bradykinesia during the finger tapping test, without cues from additional examination or history.

Methods: 21 movement disorder neurologists rated finger tapping bradykinesia, by Unified Parkinson's Disease Rating Scale (MDS-UPDRS) and Modified Bradykinesia Rating Scale (MBRS), in 133 videos of hands: 73 from 39 people with idiopathic PD, 60 from 30 healthy controls. Each neurologist rated 30 randomly-selected videos. 19 neurologists were also asked to judge whether the hand was PD or control. We calculated intraclass correlation coefficients (ICC) for absolute agreement and consistency of MDS-UPDRS ratings, using standard linear and cumulative linked mixed models.

Results: There was only moderate agreement for finger tapping MDS-UPDRS between neurologists, ICC 0.53 (standard linear model) and 0.65 (cumulative linked mixed model). Among control videos, 53% were rated > 0 by MDS-UPDRS, and 24% were rated as bradykinesia by MBRS subscore combination. Neurologists correctly identified PD/control status in 70% of videos, without strictly following bradykinesia presence/absence.

Conclusion: Even experts show considerable disagreement about the level of bradykinesia on finger tapping, and frequently see bradykinesia in the hands of those without neurological disease. Bradykinesia is to some extent a phenomenon in the eye of the clinician rather than simply the hand of the person with PD.

Keywords: MBRS; MDS-UPDRS; Parkinson’s disease; bradykinesia; finger tapping; interrater reliability; intraclass correlation coefficients.

Fig. 1

Histogram showing the distribution of MDS-UPDRS finger tapping scores for all ratings of the hands of people with Parkinson’s (orange bars) and control participants (blue bars).

Fig. 2

Histograms showing the distribution of MBRS finger tapping scores for all ratings of the hands of people with Parkinson’s disease (orange bars) and control participants (blue bars).

Fig. 3

Distribution of movement disorder specialist MDS-UPDRS ratings for finger tapping videos. Each circle represents a video rating (jitter applied to aid visualization). Orange circles: people with Parkinson’s. Blue circles: healthy control participants. Videos are ordered on the x-axis by the video random effect size according to cumulative linked mixed model, CLMM (i.e., by severity of bradykinesia). It can be seen that there is considerable variation in clinician ratings.