Apathy in Parkinson's disease with REM sleep behavior disorder

Abstract

Objectives: Rapid eye movement (REM) sleep behavior disorder (RBD) in patients with Parkinson's disease (PD) is associated with increased risk of non-motor symptoms. However, the association between RBD and apathy in PD remains unclear.

Aims: To compare the prevalence and severity of apathy symptoms in PD patients with RBD (PD-RBD+) and without (PD-RBD-). In addition, we explored the association between apathy, depressive symptoms and RBD, taking into consideration the concomitant influence of demographic, disease- and therapy-associated variables.

Methods: Sixty-four PD patients were evaluated with systematic motor (unified Parkinson's disease rating scale, UPDRS-III) and non-motor assessments. The diagnosis of RBD was based on the international consensus criteria using video-polysomnography. Apathy, sleepiness, depressive symptoms and cognitive performance were assessed using the Starkstein apathy (SAS, cut-off = 14), the Epworth sleepiness (ESS), the Hamilton depression (HAM-D, cut-off = 9) scales and the mini-mental state examination (MMSE), respectively.

Results: Among 64 patients, 26 (40%) had RBD. In the PD-RBD+ group, apathy symptoms were more frequent (52% vs 42%) and more severe (14.3 ± 5.8 vs 11.2 ± 4.9, p < 0.05), especially in the females (17.3 ± 6.0 vs 11.4 ± 5.8 in males, p < 0.05) compared to the PD-RBD- group. A high percentage of patients, especially in the PD-RBD+ group (53%), had isolated apathy without increased depressive symptoms. Increased depressive symptoms were also more frequent (50% vs 20%) and more severe in the PD-RBD+ group. The two groups were comparable in respect to demographic and clinical characteristics.

Conclusions: In PD, RBD is associated with isolated apathy and increased severity of depressive symptoms, independent of medication, motor and other non-motor symptoms. Potential mechanisms underlying this association are discussed.

Keywords: Apathy; Depression; Mood disturbances; Non-motor symptoms; Parkinson's disease; REM parasomnia; REM sleep behavior disorder (RBD); Sleep-wake disturbances.