Multiple sleep disturbances are associated with apathy in individuals with Parkinson's disease

Background: Parkinson's disease (PD) is associated with both sleep disturbances and apathy, and within PD, apathy has been associated with REM behavior disorder and excessive daytime sleepiness. Whether other forms of sleep disturbance are similarly associated with apathy in PD remains unclear. This study explored associations between a broad array of sleep disturbances and apathy in 50 individuals with idiopathic PD (PD) and 48 matched controls (MC). Methods: Participants were adults aged 53-80 (Mdn = 67), 23 % female, and 96 % white. Sleep disturbances were measured with various questionnaires (ISI, PSQI, PROMIS-SD, ESS, PROMISSRI, RBDSQ). Mood was measured with the STAI and BDI-II. Apathy was evaluated using the Apathy Scale (AS). Spearman correlations and regression analyses were performed between measures of sleep disturbance and AS in the total sample and each group. Group correlations were compared using 2-sample Fisher's z test. Results: The AS total score significantly correlated with PROMIS-SRI in the total sample and multiple measures of sleep disturbance in the PD group. The apathy subscales were each significantly correlated with sleep disturbance measures in the total sample, MC, and PD groups. The correlations between several sleep and apathy values were significantly stronger in the PD group than MC. When accounting for anxiety and depression most differences were no longer significant, only the PROMIS-SRI was significantly predictive of the behavioral apathy sub score. Discussion: Evidence supports an association between sleep disturbances and apathy in individuals with PD. Specifically, insomnia severity, poor sleep quality, and daytime sleepiness were uniquely associated with apathy in this group. We did not find these associations in the matched control group. Anxiety and depression are likely involved in the association between sleep and apathy in PD. Experimental studies that manipulate or improve sleep may further elucidate the mechanisms underlying the association between sleep disturbance and apathy in PD.