Rhythmicity And Instability of Mood-Related Symptoms in Major Depressive Disorder

Abstract

Introduction: Major depressive disorder (MDD) is among the leading causes of disability worldwide, with a multifactorial pathophysiology spanning areas of biological, psychological, and social factors. One of the neurobiological theories behind the pathophysiology of depression is the disturbance of circadian rhythms, which include changes in sleep, activity, meal timing, and social patterns. MDD often presents with a large heterogeneity in symptomatology and mood variation is one of its key symptoms. As such, investigating diurnal patterns and variation of mood-related symptoms is necessary in understanding the experience of MDD. The revised Mood Rhythm Instrument (MRhI-r) is a useful tool for assessing self-perceived rhythmicity in 24-hour patterns across multiple symptom domains, with the perception of Sleepiness playing a central role in connecting symptoms. In this thesis, the psychometric properties of the MRhI-r were investigated in individuals with MDD. Differences in the frequency and timing of peaks of mood-related symptoms were compared between individuals with MDD and controls, with a focus on the relation of objective sleep regularity with subjective rhythmicity of Sleepiness. Furthermore, select symptoms from the MRhI-r were assessed in a more nuanced fashion to elucidate instability in symptom levels. Results: Psychometric analysis of the MRhI-r in a clinical sample of individuals diagnosed with MDD revealed three symptom domains: affective (Anxiety, Irritability, Pessimism, Sadness), cognitive (Concentration, Energy, Memory, Problem solving), and somatic (Appetite, Sleepiness). When compared to controls, individuals with MDD reported significantly more peaks in affective symptoms (Anxiety, Pessimism, Sadness), as well as Problem solving and Appetite. They also reported significantly more peaks of Sadness and Appetite in the evening. While the majority of controls reported Sleepiness peaks in the evening, individuals with MDD were scattered throughout the day. Furthermore, individuals with MDD experienced lower objectively-measured sleep regularity than controls when they recognized a peak of Sleepiness. Greater within-day and between-day instability of affective symptoms was associated with worse depression and anxiety, whereas this relationship was seen only for between-day instability of cognitive and somatic symptoms. Conclusion: These results suggest that greater variation in mood is associated with worse depressive outcomes. Specifically, diurnal rhythmicity of mood-related symptoms is more apparent in individuals with diagnosed MDD.