This study is the first to examine the performance of the English language version of the Lille Apathy Rating Scale (LARS) in assessing apathy in PD by comparing it to the AS within a sample of patients with PD in the United States. Although the AS is a recommended screening measure for apathy that can be administered to large numbers of patients in a relatively short period of time, it does not provide information about the different clinical manifestations (i.e., cognitive, behavioral, affective) of apathy. The LARS represents a potentially useful instrument in characterizing the PD apathy syndrome. We found the LARS to be a moderately reliable and valid measure of apathy in our sample of patients with PD. The instrument exhibited good between-item and between-subscale correlations as well as split-half reliability, suggesting that it measures a coherent construct. Global scores were highly correlated to AS scores with an ICC greater than 0.70, indicating strong convergent validity. It correlated more highly with the AS than with the BDI-II, correlating with the latter with an ICC less than 0.70, which suggests that the LARS measures apathy per sé rather than global psychological symptomatology or depression.
We compared the LARS to the commonly-used AS using the authors’ proposed cut-off score as well as that identified using the ROC plot in our sample. Although the authors’ cut-off score of −16 demonstrated excellent specificity and positive predictive value compared to the AS cut-off of 13 of 14, its sensitivity was very poor. Many patients who scored 14 or higher on the AS did not score −16 or higher on the LARS (false negatives). This discrepancy is likely attributable to the designers’ deriving a cut-off score by comparing patient scores to judgments made by two clinicians based on interviews with the patient and family member. Although the authors suggest that a cut-off score of −16 indicates “clinically significant apathy,” their extended classification system defines a lower range of scores (−21 to −16) as indicative of “mild apathy.”
The LARS cut-off value determined to possess the best operating characteristics when compared to the AS in our sample was −22. Using this value, the instrument demonstrated similar specificity and positive predictive value and higher sensitivity and negative predictive value. This cut-off score may be better for comparing apathy prevalence to the many studies that have used the AS.
We identified the presence of apathy in 46% of our sample using the AS, which is consistent with previous reports of patients with PD.1,8,18,19
However, this number does not necessarily reflect the true prevalence of apathy in patients with PD because our sample was not randomly selected. Specifically, 61% of our sample comprised candidates for DBS surgery who differed (only from the 15 clinical trial patients) in motor symptom, apathy, and depression severity. Consistent with the findings of Sockeel et al., we found that apathy, as measured by the AS, was most strongly related to the LARS composite subscores of intellectual curiosity and action initiation, which the authors suggest might reflect cognitive and behavioral dimensions of apathy, respectively.9,20
Comparisons between the four LARS composite sub-scores and other patient variables (i.e., depression severity, motor functioning, disease duration, levodopa equivalent dose) revealed that apathy was related to the severity of depression and the severity of motor symptoms “on” medications. It should be noted that some of these variables were only available for a subset of our sample, as they were obtained from an IRB-approved MDC database (see note). Interestingly, apathy was not related to levodopa equivalent dosage (LED), motor severity “off” medications, or patient report of PD symptom duration in our sample. Apathy has been found to be greater in patients tested off levodopa medications; however, these authors did not report on a relationship between LED and apathy.21
It has been suggested that apathy may emerge after deep brain stimulation surgery for PD as a result of the reductions in levodopa medications following surgery or DBS itself.22–26
However, research on post-DBS apathy is conflicting due, in part, to methodological limitations.27
Future research is needed to characterize how these important variables interact over the disease course.
An important limitation of this study lies in the use of the AS to classify patients as apathetic, rather than formal diagnostic criteria. Unfortunately, such criteria do not yet exist, although some have been recommended by Starkstein and colleagues.7,28
An important goal in future studies on assessing apathy in PD should aim to validate such criteria, taking into consideration different models of apathy. As a result, our analyses cannot determine the diagnostic utility of the LARS. A related limitation lies in the self-report format of the AS. Patients suffering from dementia and severe apathy may lack the awareness required for valid reporting.29
Although a subset of the present sample believed to be representative did not evidence dementia on average, as determined with a dementia rating scale (DRS-2), 5 of these 35 patients scored below the suggested cut-off for possible dementia (i.e., below 130).
In conclusion, this study represents the first to examine a new, multidimensional, semistructured interview for the assessment of apathy in PD in the U.S. It is also the first to compare the LARS to the commonly-used and recommended AS. Results suggest that it is a coherent instrument with good convergent and divergent validity as well as moderate utility in identifying apathy amongst patients with PD. Although apathy is commonly regarded as a multidimensional construct comprising several domains (i.e., behavioral, cognitive, and affective), little research has aimed to empirically demonstrate the separability of these manifestations in PD, neurobiologically or behaviorally. The first step toward establishing correlates of these domains requires a reliable and valid method of their assessment. In addition, given that the relative prominence of different apathy domains across individuals may have important treatment and prognostic implications, the clinical value of an instrument that can adequately quantify and differentiate these symptom classes is clear. Future research should attempt to explore the utility of the LARS in shedding light on the multiple dimensions of the PD apathy syndrome and their relationships with the disease process and patient quality of life.