Impaired attention predicts falling in Parkinson's disease☆
Introduction
Falls are common in Parkinson's disease (PD) occurring in 33–68% of subjects with the disease. Prospective studies [1], [2] suggest a higher incidence of falls than data based on retrospective questioning [3] and are likely to be a truer representation of fall frequency in these subjects. Falls result in injury, loss of independence and reduction in quality of life. Disease duration, severity of extrapyramidal motor symptoms and a history of previous falls are significant risk factors for further falls, with a complex ‘U shaped’ reduction in falls in the later stages of the disease due to reduced independent mobility [1], [2], [4], [5].
Cognitive deficits, in particular deficits of attention and executive function, may also contribute to falls in PD. Vigilance and cognitive reaction times are impaired in subjects with PD and dementia [6], and fluctuation in attention with time has been demonstrated in PD subjects with and without dementia [7]. These attentional deficits appear to be associated with impaired gait and balance; mental distraction leads to increased postural sway in fallers with PD compared to non-fallers [8], and multiple tasking leads to freezing of gait or loss of balance in PD subjects when walking [9]. Most studies documenting the association of gait and balance with attentional deficit in PD have, however, been observational studies performed in a laboratory environment with outcome measures focussed on gait and balance assessment tools.
We were interested in whether the potential association between reduced or fluctuating attention and gait instability documented in these laboratory studies would equate to an increased risk of falls in real life.
This study was a prospective study of falls and attention in PD, measured over a 1 year period in a large community based cohort of PD patients.
Section snippets
Methods
Subjects meeting UK Parkinson ’s Disease Society Brain Bank Criteria for PD were recruited to the study. Eighty nine subjects were identified from a community based cohort (methods described elsewhere) [10]. One hundred and six patients registered with General Practitioners outside the community screening area were identified by a parallel screen of the hospital and PD clinic records and were invited to participate. Eighty seven patients were recruited through this route. There were no
Results
Of 176 study participants, four died during the 12 month observation period and eight withdrew from the study, leaving a total of 164 completed fall diary datasets (93.2% response rate).
The mean age of those completing the fall diaries was 71.2 years (SD 7.84) and 103 (62.8%) were male. Mean disease duration was 7.2 years (SD 6.4), with mean UPDRS III score 19.0 (SD 7.9) and MMSE score 25.1 (3.5).
One hundred and twenty nine subjects (78.7%) were taking levodopa, with a mean daily dose of 459.8
Discussion
Previous studies have demonstrated that multiple tasking leads to freezing of gait or loss of balance when PD subjects are walking [9], [17]. Deficits in attention may exacerbate the difficulties with multitasking and contribute to falls. In the current study, we have shown that the association of attentional deficits with postural instability translates into increased fall frequency measured prospectively over a long (1 year) study period.
The association with reaction time variability may have
Acknowledgement
The study was funded by a grant from The Healthcare Foundation. Dr. Allcock was supported by a National Health Service Research and Development Training Fellowship. Keith Wesnes is Chief Executive and sole shareholder of Cognitive Drug Research Ltd., supplier of the CDR cognitive test battery used in this study. The remaining authors report no conflicts of interest.
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Disclosure: Keith Wesnes is Chief Executive and sole shareholder of Cognitive Drug Research Ltd., supplier of the CDR computerised test battery used in this study. The remaining authors report no conflicts of interest.
Statistical analysis: Dr. L.M. Allcock (corresponding author) performed the simple statistics required for demographic comparisons. Dr. I.N. Steen (Statistician – Institute of Health and Society, University of Newcastle upon Tyne) advised on and performed negative binomial regression.