Recurrent falls are a common problem in people with PD affecting around 70% of people with PD who fall (). However, there is substantial variability in the falling rates reported in the studies included in this paper, with the proportion of fallers (single and recurrent) ranging from 35 to 95%. This high variability in reported falling rates may be attributable in part to the specific inclusion criteria used in different studies. The study with the highest proportion of fallers included only participants who had PD with dementia [20
]. The study with the next highest portion of fallers (86%) included only participants who had experienced more than one fall in the past year, meaning that retrospectively the entire sample was recurrent fallers [29
Differences in the method of monitoring falls could also contribute to the variability seen in fall rates across the included studies. The falls diary is the preferred method of falls monitoring [9
] as it enables falls to be recorded immediately after they have occurred, minimizing the chance of participants forgetting to report a fall. Only 14 (64%) of the included studies used a falls diary or similar monitoring system (e.g., postcards or calendars) [2
]. Several other studies used methods, such as telephone interviews, where participants were required to recall the falls they had experienced over a particular time frame [18
]. Where the time period to be recalled is long, the number of falls reported may be underestimated. Retrospective studies have reported rates of falls per recurrent faller per year of 3.4 and 5.0 [41
]. This is similar to the lowest number of falls per recurrent faller per year (4.7) reported by a prospective study included in the present review [23
], which collected falls data using a 6 monthly telephone call. In research involving the general older population it has been suggested that notification of falls should occur at least monthly [43
]. However, the high prevalence of cognitive impairment [44
] and the high frequency of falls experienced by some individuals with PD suggest that a recording system where falls are documented immediately should be used in this population.
Variations in classifying fallers were attributable to differences in the definition of what constitutes a fall as well as differences in the way fall categories were defined. Most studies adhered to aspects of the definition recommended by the Kellogg International Work Group [37
] for use with the older population. However, some studies deviated from this definition or did not stipulate how a fall was defined (). Additionally, this paper found substantial variability in the way that fallers were categorized. For example, nonfallers and single fallers have been combined under the categories of “nonrecurrent fallers” [33
] and “nonfallers” [28
]. While authors use different categories depending on the purpose of their study, the inconsistent categorization of participants is ambiguous and makes comparisons between studies more difficult. This problem could be addressed by standardizing the categories used in future studies. For example, Thomas et al. [17
] categorized recurrent fallers according to the number of falls in three months including; “infrequent fallers” (2 to 4 falls), “frequent fallers” (5 to 15 falls), and “very frequent fallers” (>15 falls). The categories of “nonfallers” (0 falls) and single fallers (1 fall) could be added to this to cover the spectrum of fall rates seen in people with PD.
Substantial variability is also seen in the length of time over which falls data is collected, with the reporting period in the included studies varying from 1 to 29 months. In the present paper, fall rates were adjusted to an approximate yearly rate to facilitate comparison between studies (). However, this adjustment does not account for disease progression. It seems likely that, as disease severity increases over time, falling rates will also increase [2
] until the individual becomes immobile [19
]. Consequently, the adjustments used to provide annual fall rates for this review potentially underestimate the rate in studies with a reporting period of less than twelve months [2
] and overestimate the rate for the study with a reporting period of longer than twelve months [34
]. In order to facilitate comparison of future studies with varied reporting periods, it is recommended that fall data be reported at predetermined intervals. A consensus meeting of experts regarding the general older population recommended that falls be monitored for 12 months [43
]. No such review has been undertaken regarding the PD population specifically, although a shorter time period is considered acceptable as people with PD fall more frequently than the general older population [18
This paper has summarized factors associated more strongly with recurrent fallers than single and nonfallers (). Disease severity was found to be significantly associated with recurrent falls [2
] and to be a predictor of future recurrent fallers [2
]. A previous review of prospective studies of falling in PD [12
] also found that, as the UPDRS motor score increased, the risk of falling increased until the UPDRS score reached around 50 points. Thereafter the risk of falling largely stabilized, with a possible slight reduction in risk with severe disease. The authors speculated that the inclusion of more participants from institutionalized care could result in a further decrease in fall risk with severe disease severity due to the limited mobility of these types of participants. Similarly, the participants included in this paper were mostly community dwelling with mild-to-moderate levels of disease severity. Only one of the included studies [32
] examined falling in participants in institutional care. The relationship between disease severity and falls in people with more severe disease, including those requiring care in an institution, requires further investigation.
Allcock et al. [15
] demonstrated an association between fall frequency and impaired attention. It was suggested that impaired attention may contribute to falls by increasing difficulty with performance of concurrent tasks, which may inhibit the performance of compensatory movements to prevent a fall [15
]. However, a recent prospective study with a large sample of people with PD (n
= 263) has found that deterioration in gait under dual task conditions was not associated with future falls [50
]. Further research is needed to clarify the clinical implications of the association between cognitive impairment and recurrent falls.
Increased fear of falling has been associated with recurrent falls [18
]. This may occur as fear of falling can lead to self-induced restriction of activity [51
] resulting in deconditioning and reductions in muscle strength which may increase fall risk [13
]. However, there is some evidence that not all recurrent fallers are fearful of falling. In a recent retrospective study [17
] two participants who fell very frequently (falling 210 and 360 times each within 3 months) were found to have the lowest fear of falling, even when compared to those who fell rarely (0-1 fall). It was suggested that the experience of very frequent falling with no significant injury or negative consequences could lead to complacency and a resultant lack of fear of falling. Alternatively, low fear of falling could result in risk taking behavior and so contribute to increased incidence of falls. Future prospective studies could seek to clarify this relationship between fear of falling and fall frequency.
This paper identified several factors that have been found to be associated with prospectively recorded recurrent falls, including a positive fall history [2
], increased disease severity [2
], motor impairment [18
] and duration [34
], treatment with dopamine agonists [15
], increased levodopa dosage [34
], cognitive impairment [15
], fear of falling [18
], freezing of gait [23
], impaired mobility [18
], and reduced physical activity [34
]. While these factors are also known to be associated generally with falls in PD [12
], the results of the studies included in this paper suggest that as these factors progress there is an increased tendency for recurrent falls to occur. However, the presence of these associations does not explain why a person with PD who falls occasionally begins to fall recurrently. There is a need for further prospective studies to be conducted which use multivariable regression to investigate the factors that were identified to be relevant in the present paper and their contribution to recurrent falling. Such work would aid in developing an understanding of the causes of recurrent falls. In addition, consideration of factors associated with recurrent falling reported in retrospective studies, including lower limb muscle power [52
], impaired motor planning [14
], and urinary urge incontinence [42
], requires prospective investigation to confirm these relationships. Similarly, the role of medication-related side effects, such as dyskinesia [2
] and orthostatic hypotension [54
], requires further prospective evaluation regarding their role in recurrent falls in PD.
4.1. Clinical Implications
Several risk factors for falls have been found to be more strongly associated with recurrent falls than single falls, suggesting that individuals who fall recurrently may benefit from different fall reduction interventions than single or nonfallers. Some of the factors associated with recurrent falls are potentially modifiable, including cognitive impairment [55
], freezing of gait [57
], fear of falling [29
], reduced mobility [58
], reduced physical activity [29
], and balance impairment [58
]. However, while there is evidence that these factors can be improved with intervention, it remains to be determined whether such improvements would result in reductions in fall frequency, particularly in recurrent fallers.
Given the inconsistent relationship between fear of falling and recurrent falls, it is recommended that fear of falling be assessed in all recurrent fallers and interventions provided accordingly. For example, where fear of falling is found to be high compared to actual fall risk, intervention to reduce fear of falling may be considered. Cognitive behavioral therapy used in conjunction with physical training has been shown to be effective in decreasing fear of falling in the general older population [60
] but has not been investigated in the PD population.