The pathoplasticity of dysphoric episodes: differential impact of stressful life events on the pattern of depressive symptom inter-correlations

Abstract

Background: Previous research has shown that stressful life events (SLEs) influence the pattern of individual depressive symptoms. However, we do not know how these differences arise. Two theories about the nature of psychiatric disorders have different predictions about the source of these differences: (1) SLEs influence depressive symptoms and correlations between them indirectly, via an underlying acute liability to develop a dysphoric episode (DE; common cause hypothesis); and (2) SLEs influence depressive symptoms and correlations between them directly (network hypothesis). The present study investigates the predictions of these two theories.

Method: We divided a population-based sample of 2096 Caucasian twins (49.9% female) who reported at least two aggregated depressive symptoms in the last year into four groups, based on the SLE they reported causing their symptoms. For these groups, we calculated tetrachoric correlations between the 14 disaggregated depressive symptoms and, subsequently, tested whether the resulting correlation patterns were significantly different and if those differences could be explained by underlying differences in a single acute liability to develop a DE.

Results: The four SLE groups had markedly different correlation patterns between the depressive symptoms. These differences were significant and could not be explained by underlying differences in the acute liability to develop a DE.

Conclusions: Our results are not compatible with the common cause perspective but are consistent with the predictions of the network hypothesis. We elaborate on the implications of a conceptual shift to the network perspective for our diagnostic and philosophical approach to the concept of what constitutes a psychiatric disorder.

Fig. 1

A dysphoric episode (DE) according to a common cause (a) and a network (b) perspective. (a) The common cause DE causes the six symptoms (d1–d6) of a dysphoric episode. Stressful life events (SLE1 and SLE2) influence the symptoms of a dysphoric episode only indirectly, via the common cause DE. (b) A dysphoric episode is a network in which symptoms d1–d6 are directly connected with one another. SLE1 and SLE2 influence the symptoms of a dysphoric episode directly.

Fig. 2

Correlation networks between the symptoms of a dysphoric episode for the four stressful life event groups. The top left depicts the network after stress; the top right after a romantic loss (RomLoss); the bottom left after health problems; and the bottom right after an interpersonal conflict. Each symptom is represented as a node in the networks and a connection between two symptoms represents the tetrachoric correlation between them. The connection is green when the correlation is positive and red when the correlation is negative. depr, Depressed mood; inte, loss of interest; wlos, weight loss; wgai, weight gain; dapp, decreased appetite; iapp, increased appetite; isom, insomnia; hsom, hypersomnia; pagi, psychomotor agitation; pret, psychomotor retardation; fati, fatigue; wort, feelings of worthlessness; conc, concentration problems; deat, thoughts of death.

Fig. 3

Centrality of symptoms in the four stressful life event groups. The top left panel depicts symptom centrality after stress; the top right panel after a romantic loss (RomLoss); the bottom left panel after health problems; and the bottom right panel after an interpersonal conflict. The x-axis represents the 14 disaggregated symptoms of a dysphoric episode while the y-axis represents centrality (defined as the sum of tetrachoric correlations between a symptom and all the other symptoms in the network). depr, Depressed mood; inte, loss of interest; wlos, weight loss; wgai, weight gain; dapp, decreased appetite; iapp, increased appetite; isom, insomnia; hsom, hypersomnia; pagi, psychomotor agitation; pret, psychomotor retardation; fati, fatigue; wort, feelings of worthlessness; conc, concentration problems; deat, thoughts of death.