A combination of balance tests and UPDRS items that relate to PIGD predicted balance confidence in PD subjects, as measured by ABC scores, better than any single balance test or UPDRS‐PIGD item. In the regression model that included items 27–30 of the UPDRS, the pull test, gait item, and posture item significantly improved the prediction of ABC scores, suggesting that each of these items assesses different aspects of balance control relating to a PD subject's balance confidence. When the one‐leg stance test and the functional reach test were added to the regression model, the one‐leg stance test replaced the posture item as a significant contributor to the prediction of ABC scores. Both combinations, however, provided similar correlations among actual and predicted ABC scores. Therefore, it may only be mildly useful to add the one‐leg stance test to the UPDRS motor exam in order to predict balance confidence.
The ability to discriminate subjects with high or low balance confidence is important for several reasons: (i) balance confidence correlates with balance impairment in PD,7
(ii) physically active subjects report higher ABC scores than those who are less active,11,13,14
and (iii) compared with subjects who report high balance confidence on the ABC scale, subjects with low balance confidence are nearly twice as likely to fall within the next 2 years.15
Therefore, there may be a benefit in administering a combination of balance tests and UPDRS‐PIGD items (with, perhaps, the ABC questionnaire), because, together, they may provide a more accurate assessment of how balance impairments due to PD affect a subject's choice of daily activities and provide insight about that subject's risk for future falls.
Assessing multiple balance tests and UPDRS items also improved predictions of the subjects' fall history. A combination of the one‐leg stance test and the gait item of the UPDRS provided the optimal regression model for identifying subjects as fallers or non‐fallers by accurately identifying the fall history of the most subjects with the fewest significant predictor variables. As significant predictors within the same model, the one‐leg stance test and the gait item of the UPDRS must have assessed different balance impairments that contributed to the falls of different subsets of PD subjects, thereby identifying the fall history of more subjects together than when considered separately. In support of this notion, the one‐leg stance test was the most sensitive predictor for identifying fallers, whereas the gait item of the UPDRS was more specific for identifying non‐fallers. Therefore, combining a balance test that was sensitive to subjects who had fallen with a balance test that was specific to subjects who had not fallen may have improved the models' predictions of fall history by providing complementary, multi‐factorial assessments of the subjects' postural instability.
For the one‐leg stance test, a cut‐off time of 10 s provided the best combination of sensitivity and specificity for fall history in the PD subjects, consistent with a previous report by Smithson et al
who reported that PD subjects with a history of falling, on average, exhibited one‐leg stance times of under 10 s, and PD subjects without a history of falling, on average, exhibited one‐leg stance times of about 15 s.5
In addition to the one‐leg stance test's ability to accurately predict the PD subjects' fall history, the one‐leg stance test and the arise from chair item were also the most informative tests for predicting subjects with a history of only one fall. Because the one‐leg stance test and the arise from chair item both evaluate a subject's ability to make a transition from a large base of support to a small base of support, this result suggests that an impaired ability to shift to a smaller base of support coincides with the onset of falls in PD subjects. Thus, evaluating PD patients during base‐of‐support transitions may allow clinicians to identify subjects at risk for falls earlier than with the pull test, thereby providing an opportunity to institute therapies before the patients become injured or disabled by recurrent falls. A long term, prospective assessment of falls, however, would be necessary to establish the one‐leg stance or arising from a chair as tasks that predict future falls in PD subjects.
Although we did not record the circumstances surrounding the subjects' falls, we suspect that the context of the subjects' falls affected the relative strength of each balance test's ability to predict the subjects' fall history. PD subjects fall most when turning, when getting out of a bed or chair, or when walking, followed by falls due to external perturbations (for example, from a slip or trip).3
Therefore, the one‐leg stance test, the gait item, and the pull test were likely informative of the subjects' fall history because they assess balance during tasks similar to those which are the most troublesome for PD subjects.
The results demonstrate that many UPDRS items and balance tests are capable of relating to a subject's balance confidence and fall history, regardless of the subject's medication state at the time of testing. The balance tests, however, may be more informative when testing subjects in a certain medication state, and some tests may be more sensitive than others to changes in a subject's medication state. Therefore, because we did not control for the subjects' medication dose cycle, the results reported in this study may represent underestimations of the balance tests' ability to predict balance confidence and fall history.
Compared with individual balance tests or individual UPDRS items related to PIGD, multiple balance tests and UPDRS‐PIGD items improved the assessment of balance confidence and fall history. The one‐leg stance test, the pull test, and the gait item of the UPDRS, together, represented the most informative measures of balance confidence and fall history, perhaps because (i) the tests assess different aspects of postural stress related to falling, and (ii) the tests provide additional sensitivity and specificity for postural instability. Therefore, we recommend that clinicians evaluate postural stability in PD patients using the one‐leg stance test, the pull test, and the gait item of the UPDRS motor exam.