Prevalence of depression in Parkinson's disease: Effects of disease stage, motor subtype and gender

Abstract

Depression is one of the most common non-motor symptoms of Parkinson's disease (PD) with a large negative impact on the quality of life. Factors such as disease stage, subtype of PD and gender might play an important role in the prevalence of depression, but a large study investigating all these factors in a within-subject design is lacking. Therefore we studied a homogeneous group of 256 Dutch PD patients (60% men, mean age = 65.12 (± 9.6) years). In total, 36.3% of the subjects had a BDI-score indicative for a minor depression, while 12.9% had a major depression. Notably, only 8.6% of the minor depressed patients and 30.3% of the major depressed patients were taking antidepressants. A higher prevalence of depression was observed in the later stages of the disease. However, this finding was absent in a smaller subsample after correction for cognitive impairment. Our data did not show a difference in the prevalence of depression between the motor subtypes and showed a trend towards higher prevalence of depression in the tremor dominant group. There was no significant difference in the prevalence of depression between men and women. We will discuss the relevance of these results in relation to the findings of other studies.

Introduction

With an average prevalence of about 40% [1], depression is one of the most common non-motor symptoms of Parkinson's disease (PD) [2], which impacts quality of life tremendously [3], [4], [5]. A variety of studies have tried to understand the characteristics of depression in PD. Yet, there is evidence that depressive symptoms in PD patients often remain untreated [6], [7], underlining the need to understand the factors that play a role in the prevalence of depression in PD.

The prevalence of depression has been investigated in relation to the staging of PD, but literature is inconclusive. A bimodal distribution has been reported with the highest percentages of depression occurring in the early and late stages of PD [8], [9], [10]. While onset of depression during the late stages has mainly been related to a broader monoaminergic deficit in combination with higher occurrence of cognitive impairment [11], occurrence early in the course may be a reactive depression due to the impact of the diagnosis. Nevertheless, depression may already occur before the onset of motor systems [12], [13] suggesting that the neuropathological process of PD itself increases the risk of depression. In contrast to these findings, several others reported a linear relationship between depression and disease stage [14], [15], [16], [17].

Patients with PD can be classified into subtypes according to their motor symptoms like ‘tremor dominant’, ‘hypokinetic-rigid’, or ‘postural instability-gait disorder’ (PIGD) dominant [18], [19], [20] which might have a different progression of neuropathology [11]. Several studies have reported an association between depression and different motor symptoms, such as tremor [15], [16], PIGD [15], [21], [22] and hypokinesia-rigidity [16], [23], [24]. However, other studies did not find a difference in depression prevalence among the different motor symptoms [10], [25].

In the general population, women have consistently been shown to have a twofold chance to develop a depressive disorder compared to men [26]. As a different neurobiological mechanism in developing depression might be present in PD compared to the general population, gender differences in the prevalence of depression in PD might be eliminated. Indeed, several studies have reported no gender difference for the development of depression in PD, but have not specifically addressed potential reasons for this [9], [14], [27]. A direct investigation of the relationship between gender specific prevalence, disease stage or subtype of PD is still lacking in a homogeneous sample. In light of the aforementioned findings, the aim of this study was to extend recent studies investigating the association between depression and disease stage in PD, motor subtype, and gender using a large pool of well-characterised patients.