The Concurrent Validity of the Dual-Task l-Test in Parkinson’s Disease and its Predictive Ability in Identifying Falls

Introduction: People with Parkinson’s Disease (PD) often have difficulty completing dual-tasks due to reduced automaticity of movement, which consequently increases falls risk. Further outcome measures (OMs) are required to enable assessment of dual-task mobility.

Aims and Objectives: Primary aim: To establish the concurrent validity of the L-Test-MANUAL and L-Test-COGNITIVE with the TUG-MANUAL and TUG-COGNITIVE in participants with idiopathic PD. Secondary aim: To determine the predictive ability of the L-Test, L-Test-MANUAL and L-Test-COGNITIVE in identifying fallers.

Methods: Twenty-five patients with idiopathic PD were recruited to the study and categorised into faller (28%, n=7) or non-faller (72%, n=18) groups. Participants completed the following tests: L-Test-STANDARD, L-Test-MANUAL and L-Test-COGNITIVE, and TUG-STANDARD, TUG-MANUAL and TUG-COGNITIVE. Time taken to complete each of the tests was measured and dual-task cost (DTC) was calculated. Mean differences for fallers and non-fallers were calculated using independent t-tests or the Mann-Whitney U test. Spearman’s Rank Order Correlation Coefficients were calculated to determine the relationship between the L-Test and TUG manual and cognitive dual-task conditions. Receiver operating characteristic (ROC) curve analyses with 95% CIs were used to describe model discrimination for each of the L-Test and TUG conditions. The area under the curve (AUC), sensitivity and specificity values and cut-off scores were established for identifying fallers versus non-fallers.

Results: The L-Test-STANDARD, L-Test-MANUAL and L-Test-COGNITIVE correlated very strongly with the TUG-STANDARD, TUG-MANUAL and TUG-COGNITIVE (rho=0.94, p<0.001, rho=0.94, p<0.001 and rho-0.92, p<0.001 respectively). There was no significant difference between fallers and non-fallers in time taken to complete the tests (p≤0.05) or in DTC scores (p≤0.05). Inspection of boxplots and of 25^th and 75^th percentile scores provided no indication of either a ceiling or floor effect respectively. Univariate regression analysis demonstrated that none of the tests had the ability to distinguish between fallers and non-fallers (p≤0.05). The L-Test and TUG single-task conditions had the greatest estimates of sensitivity (71.4% and 85.7% respectively) and specificity (72.2% and 61.1% respectively) in identifying falls risk. Cut-off scores were established for falls risk for the single-task L-Test (≤23 seconds) and the single-task TUG (≤9.2 seconds).

Conclusions: L-Test single and dual-task conditions were very strongly correlated with those of the TUG. There was no evidence of a ceiling effect for any of the tests this cohort of participants with mild-moderate PD. None of the L-Test or TUG conditions were able to distinguish between fallers and non-fallers.

Implications of Findings: The manual dual-task and cognitive-dual task L-Test conditions correlated very highly with the corresponding TUG conditions, indicating their suitability for use in PwP of mild-moderate disease severity in the assessment of dual-task mobility. However, none of the test conditions was able to distinguish between fallers and non-fallers in this study. Future studies with larger sample sizes and greater numbers of fallers are necessary to determine whether the L-Test dual-task conditions have the ability to identify fallers.