Chronic Anergic Depression IDentification - Magnetic Resonance Imaging Exploration in the Elderly of Traits Related to Onset

Depression in the elderly, or "late life depression" (LLD), is often considered to be homogeneous, legitimizing standardized treatment. Yet the literature suggests that there are different forms of LLD, with different pathophysiology, course and treatment. Our experience has led us to identify an "anergic" form, marked by adynamia and anhedonia (anergic depression, AnD). Highly represented among LLDs, it readily resists the usual antidepressants, so that its course is often chronic. Thanks to the "Chronic Anergic Depression Open Trial", the investigators were able to show that AnD responds to dopaminergic (DA) molecules. Therefore the invastigators hypothesized a pathophysiology linked to dysfunction of the mesolimbic DA system. However, not all patients would present the same form: two subgroups could be isolated, each contributing equally. The first corresponds to patients for whom the episode is a recurrence, the so-called "early onset depression" (EOD). The first episode occurs at 34 ±16 years of age and is frequently associated with a personality disorder (73%). The index episode usually lasts 6 ±3 years and is typically associated with anxiety (96%). The second group corresponds to the onset of primary depression after the age of 60, known as "late onset depression" (LOD). The index episode occurs at around 71 ±6 years of age, in people with no premorbid personality disorders. The episode is shorter (3 ±1 years) and anxiety is frequent (75%) but less marked. These patients showed a high propensity for a course compatible with synucleinopathies, but often less rapid than that of the classic forms of these diseases. The investigators hypothesize that within AnD, EOD and LOD present different pathophysiologies, and that this difference is observable on functional magnetic resonance imaging (MRI): LOD patients should present a greater reduction in functional connectivity in the mesolimbic system. The investigators make the subsidiary hypothesis that LODs also show a structural alteration observable with other types of MRI measurements, i.e. multiparametric imaging.