Profile of Functional Limitations and Task Performance Among People With Early- and Middle-Stage Parkinson Disease

Discussion

These data provide expected ranges of physical function by disease severity for measures commonly used with individuals in early and middle stages of PD. We chose these measures because they capture many of the daily tasks that people with PD commonly bring to the attention of their health care providers, such as getting in and out of bed, rising from a chair, walking, maintaining balance, and turning to look behind while driving.

The data provide clinicians and researchers with a context for interpreting functional limitations of people with PD. Clinicians also can use the data to identify individuals who perform outside of anticipated mean and median scores for specific tasks. Furthermore, these data can inform decisions regarding appropriate measures for future studies of physical intervention.

We described the data in relation to 2 different measures typically used to characterize PD severity: the UPDRS motor score and the modified H&Y scale.⁶ The UPDRS is the gold standard for experimental studies and medical management; however, extensive training is required to use this measure appropriately, it is time intensive, and the scope of information gathered is beyond that required for decisions related to physical intervention. In contrast, the H&Y score provides only a coarse estimate of disease progression but is more accessible to physical therapists. For these reasons, we chose to examine physical activities in relation to both measures.

Several insights related to the level of disease severity at which functional decline begins to emerge, choice of measures at different points in the disease course, and interpretation of measures emerged from this work. The first insight is that activity limitations occur very early in PD, as indicated by the CS-PFP, becoming progressively worse as the disease advances. This finding is of importance because most measures used with people who have PD are not as clearly responsive to early limitations in activities as is the CS-PFP.

Individuals with PD had lower CS-PFP scores compared with individuals who were healthy in the study by Cress and Meyer.²² These scores represent a substantial loss of functional capacity. Those individuals with H&Y stage 3 scores (mean age=69 years) had CS-PFP scores below 30, more than 25 points lower than scores of individuals who were healthy, indicating even greater loss of capacity.

The CS-PFP is a unique measure because it quantifies capacity for performance of daily functional activities.²² As such, this test is more likely to identify limitations that would be missed in performance of a few single tasks such as those typically used to quantify function (eg, FRT, TUG). Furthermore, the tasks included in the CS-PFP encompass a broad range of activities required for daily function.

Data from a variety of studies suggest that transition from independence to dependence occurs around a CS-PFP score of 57.²² As evidenced by median scores, a substantial number of participants in our data set had reached or exceeded this threshold by H&Y stage 2.5 and UPDRS motor score of 30.5 to 45. These findings are consistent with data of Shulman and colleagues¹ indicating a transition from preclinical disability and disability occurs for people with UPDRS total scores above 50.

It should be noted that the transition to disability specific to people with PD has not yet been established. Because time to complete tasks is important in scoring the CS-PFP, bradykinesia probably affects the overall scores substantially, bringing individuals to the transition point (score of 57) established for older adults, even though they may not be approaching disability. Nevertheless, these data underscore the degree to which PD affects overall physical capacity even very early in the disorder.

Of interest, most of these individuals continue to perform within a relatively constant rate of perceived exertion as evidenced by their RPE of ≤12, consistent with the range observed in older adults who are healthy. These findings suggest that people with PD adjust task performance to stay in the comfortable range. Only those individuals at higher levels of disease severity reported a high RPE during the relatively common functional activities of the CS-PFP. For example, the group with UPDRS motor scores of 45.5 to 60 had a mean RPE of 13.7 (SD=0.6), underscoring the degree of effort required for relatively simple tasks.

The only other measure in this study that detected losses early was the FAR. The mean FAR was 107 degrees (SD=8.6) for participants in H&Y stages 1 and 1.5 (mean age=55 years, SD=8.5). These individuals had substantially reduced FAR compared with a sample of adults without PD in which the mean FAR was 117.9 degrees (SD=14.2) for men and 127.8 degrees (SD=10.4) for women (data from 40 adults who were healthy, aged 40–59 years, 55% female), (unpublished data). By H&Y stage 3 (mean age=69 years, SD=8.0), participants were 30 degrees below the expected values for individuals of similar age who are healthy. These findings have important implications for balance and function. Axial rotation is used to maximize FRT distance³⁸; thus, it is likely that the substantially lower FAR for participants in H&Y stage 3 contributes to balance dysfunction in later stages of PD. Furthermore, limited ability to twist the torso to see behind has ramifications for any activity that requires such motions (eg, reaching for objects, turning to see while backing up a car).

Two other measures (FRT and 6MWT) showed a systematic decrease in values across stages of PD, although they did not detect decline in the participants with early signs of PD. Participants in the earliest stages of PD demonstrated an age-appropriate median FRT score (15–16 in), whereas those with UPDRS motor scores of 30 to 45 and H&Y stage 3 had a median reach of 11.3 in. The difference between H&Y stages approached 2 in. To put these data into context, Dibble and Lange³⁹ recommended a cutoff of 12.5 in in patients with PD to predict falls (sensitivity=86%). In our sample, the following percentages of participants were below this cutpoint: H&Y stage 2=11.0%, H&Y stage 2.5=51.0%, and H&Y stage 3=70.3%. These results are consistent with those of Tanji et al,⁴⁰ who also found the FRT able to distinguish between those with postural instability (H&Y stages 2.5 and 3) and those without postural instability (H&Y stage 2).

With respect to the 6MWT, the mean walk distances in our sample for participants who were least involved (H&Y stages 1–2, UPDRS motor scores=0–15) appear appropriate compared to normative values for people who are healthy.³³ A difference in mean values of nearly 200 m was observed across each UPDRS motor grouping. Our findings are consistent with those of other authors.^34,41,42 In the context of gait speed, Perry and colleagues⁴³ indicated that 0.8 m/s is a cutpoint between community ambulation and limited community ambulation for people recovering from a stroke, whereas Studenski and colleagues⁴⁴ found 1.0 m/s to be a cutpoint for predicting decline in health status and function for older adults. The groups of participants in our study with H&Y stage 3 and UPDRS motor scores of 45.5 to 60 had mean and median gait speeds (around 1.0 m/s) at or near values indicating higher risk of health problems and functional compromise.

A second important insight is that the following measures begin to show impairment relatively later in disease progression, beginning in H&Y stage 3: 2MWT, TUG, supine-to-stand test, and stand-to-supine test. Both mean and median scores suggest substantial difficulty for people later in the disorder. The data indicate that the 2MWT, in contrast to the 6MWT, is not of sufficient length to pick up the endurance problems in individuals who are in the earlier stages of PD,⁴⁵ even though deficits in economy of movement have been established for those in very early stages of PD.⁴⁶

For the TUG, scores of 10 seconds or less are generally considered normal in elderly people who are healthy.¹¹ Whether examining the mean or the median in our sample, there was a transition from scores below 10 seconds for participants who were less involved (H&Y stages 1, 1.5, and 2) to scores above 10 seconds for those in H&Y stages 2.5 and 3. The minimum score was 5.5 seconds, and the maximum score was 31.6 seconds. Only 22.5% of participants in H&Y stages 1, 1.5, and 2 had scores above 10 seconds for the TUG, whereas 53.8% of participants in H&Y stages 2.5 and 3 had scores above 10 seconds. With respect to UPDRS motor scores, the transition from below to above 10 seconds occurred at UPDRS scores of 30 of 45 points for the mean (10.3 seconds) and was similar for the median (9.8 seconds). These findings suggest that limitations in the TUG are not revealed until later in the disease progression. These findings are supported by Ellis and colleagues,⁴⁵ who reported mean TUG scores of 55 seconds in a sample of patients with PD who were predominantly (64%) in H&Y stage 4.

The stand-to-supine and supine-to-stand tests can be important practical measures, as complaints of difficulty moving in bed are common among people with PD. In this study, it was only in H&Y stage 3 or UPDRS motor scores above 45 that these tests revealed limitations. These participants were twice as slow as individuals in the early stages, although the variability was large, suggesting that not all participants in H&Y stage 3 will demonstrate limitations in this area.

A third insight relates to the considerable heterogeneity and variance in performance observed in our sample, particularly in the later stages of PD. Given this variability, individuals at either end of the measurement scale can skew the mean substantially. For some measures (eg, supine-to-stand task, 360° turn), the medians indicated much greater functional limitations than the means. Based on our findings, we suggest examining both the mean and median scores. In addition, distinguishing differences in physical function by stage of disease alone may not be sufficient. Examination of subpopulations may yield less variability and more narrow profiles. For example, categorizing by dominance of symptom (eg, postural instability gait difficulty or tremor dominant) may reveal very different functional trajectories and should be investigated in future studies.

The fourth important point relates to clinical and research recommendations for selection of functional measures across stages of PD. Choice of measures will necessarily be dictated by the purpose for which they are to be used. In the clinic, physical therapists managing patients in the early stages may consider using the CS-PFP and the FAR to identify deficits in status. The 6MWT and the FRT also could be incorporated early in the disease to establish baseline status and repeated periodically thereafter to determine performance relative to elderly people who are healthy and to expected ranges in PD. The TUG, 2MWT, and supine-to-stand measure should be reserved for patients in the moderate stages.

For intervention studies, choice of measures should be determined by both stage of PD and study length. For participants in the earliest stage of PD, only the CS-PFP and FAR detected differences from age-appropriate norms. Thus, for such participants, these 2 measures have potential to detect change of functional problems in short-term studies (less than 6 months). Conversely, other measures have low potential to detect functional problems in short-term studies in which participants are in early stages of PD. Because of the lack of responsiveness of most measures for people in the earliest stages of PD, a new measure of function, the instrumented Timed “Up & Go” Test (iTUG),⁴⁷ has been developed. The iTUG appears to be especially sensitive to deficits in balance and may provide further insight into these deficits in the earliest stages of PD.

Many of the measures in addition to the CS-PFP and FAR might be appropriate for longer-term studies (eg, 12–24 months), even when people in early stages of PD are included. Examples of such measures are the FRT and 6MWT, which could add insight into functional change as the disease progresses. The TUG, 2MWT, and supine-to-stand measure would be appropriate for studies including participants who have moderate to severe PD either at baseline or at the end of the study.

Several limitations should be acknowledged. First, most of the participants in this database were in H&Y stages 2, 2.5, and 3, with only 3% in stages 1 to 1.5. These findings were in part because people are not always diagnosed in the earliest stages of PD, and of those who are, not all are referred for exercise interventions. Second, because these data are cross-sectional (not longitudinal), we cannot make statements about change over time. Nevertheless, these data give some insight into what to expect at each point in the disease process and can help clinicians determine which deficits begin in the earliest stages as well as which measures might be of most use early in the disease process. Future investigations, utilizing change scores will be essential to further our understanding of performance in people with PD. Third, these data were derived from 5 different studies, and not all measures were performed at all sites and for all studies. Nevertheless, the sample was of sufficient size that the number of participants ranged between 100 and 252 for all measures. Finally, the participants were predominantly educated and white, with low diversity with respect to income and race, limiting ability to generalize to some extent. However the samples were recruited from 3 distinct locations across the United States, increasing generalizability from a geographical perspective.

In summary, typical values are presented relative to disease severity for standard measures of functional ability commonly used by researchers and clinicians who work with individuals in early and mid stages of PD. Findings demonstrate that functional loss occurs at different points in the disease process, depending on the task under consideration. The resulting profile of functional limitations provides benchmarks that clinicians and researchers can use to interpret and monitor status of patients.