Apathy is prevalent problem in Parkinson’s disease, but it is more evident in patients’ behavioral and social habits than in their emotional or cognitive ones, researchers in the U.K. report.
Their study, Differential impact of behavioral, social, and emotional apathy on Parkinson’s disease,” also linked behavioral and social apathy to a likelihood of depression in these people. The research was published in the journal Annals of Clinical and Translational Neurology.
Apathy is a well-recognized Parkinson’s non-motor symptom, although research rarely looks into the specific domains – behavioral, cognitive, executive, social, and emotional – it affects, or how exactly this symptom relates to depression and anhedonia (the inability to feel pleasure) seen in Parkinson’s patients.
University of Oxford researchers used the Apathy Motivation Index (AMI), a self-report measure of apathy validated in healthy individuals, to examine the multidimensional profile of apathy in Parkinson’s disease.
AMI categorizes apathy according to behavioral (the tendency to self-initiate goal-directed behavior), social (the level of engagement in social interactions), and emotional (ability to express feelings or affective responses) domains.
The team first evaluated AMI’s reliability and validity in Parkinson’s by comparing it with the Lille Apathy Rating Scale (LARS), a well-validated interview approach to assessing apathy in Parkinson’s and used in the development of AMI. Next, they evaluated if Parkinson’s patients exhibited differences in apathy domains compared to healthy controls, and if these domains associated with depression and anhedonia.
The study included 102 Parkinson’s patients (mean age 67.7; 79 men) and 147 healthy volunteers (mean age 66.1; 104 men). Mean disease duration was 6.6 years and Unified Parkinson’s Disease rating scale score was 27.0 (on a 0-199 scale, with 0 meaning no disability and 199 total disability). Neither patients nor controls had other neurological or psychiatric conditions.
Eighty-seven patients completed LARS, 84 (and 67 controls) completed the 14-item Snaith–Hamilton Pleasure Scale (SHAPS, a 14 item scale that measures anhedonia), and 80 (87 controls) completed the Geriatric Depression Scale–Short Form (GDS-15, a 15-item form to screen for depression in a variety of settings).
Results showed that AMI’s total score correlated positively with LARS’ overall score, demonstrating good construct validity, the researchers said. AMI also showed diagnostic accuracy in identifying 36 Parkinson’s patients with apathy. According to the authors, this means that AMI enables them to explore the various dimensions of apathy, while achieving an apathy prevalence rate consistent with existing studies.
Parkinson’s patients showed a higher total AMI score than healthy controls, indicating greater apathy overall. This result, as well as individual subscale scores, was not dependent on age, sex, cognition, years of education, disease duration, and levodopa doses.
Subsequent analyses revealed that patients had higher levels of behavioral and social apathy relative to controls, but not of emotional apathy. However, six patients showed deficits in emotional sensitivity and no deficits in the other domains.
Patients who were more behaviorally and socially apathetic were more likely to be depressed, a co-existing condition not observed in emotional apathy scales among patients. In healthy controls, higher the level of emotional apathy associated with lower the evidence of depression.
“This result suggests that different clinical approaches toward apathy in patients with PD compared to the general population might be needed,” the scientists wrote.
Patients with higher behavioral and social apathy also showed more evidence of anhedonia. Again, this was not found in emotional apathy. In the controls, only social apathy correlated with a reduced capacity to feel pleasure. No differences were found between patients and controls regarding anhedonia levels.
“Together our findings may help in guiding the development of more effective, selective treatments for apathy in [Parkinson’s] — including nonpharmacological ones aimed at different aspects of motivation — as well as assisting in our understanding of how apathy, anhedonia, and depression are related,” the researchers concluded.