The presence of depression in schizophrenia has been a challenge to the Kraepelinian dichotomy, with various attempts to save the fundamental distinction including evoking and refining diagnoses such as schizoaffective disorder. But the tectonic plates are shifting. Here we put forward a summary of recent evidence regarding the prevalence, importance, possible aetiological pathways and treatment challenges that recognizing depression in schizophrenia bring. Taken together we propose that depression is more than comorbidity and that increased effective therapeutic attention to mood symptoms will be needed to improve outcomes and to support prevention.Key words: schizophrenia/depression/aetiology/ transdiagnostic/psychosis
Prevalence of Depression in the Life Course of SchizophreniaThe prevalence of depressive disorder in schizophrenia has been reported to be around 40%, however the stage of illness (early vs chronic) and state (acute or post-psychotic) factors influences figures, which can thus vary considerably.1 In acute episodes rates are up to 60%, whilst in post-psychotic schizophrenia rates of moderate to severe depression vary between 20% in chronic schizophrenia and 50% following treatment of first episode.2 When examining very early phases of illness, in groups identified as ultra high risk (UHR) for psychosis, high rates of "comorbid" axis one diagnoses are reported, with over 40% reaching criteria for a depressive disorder, outweighing anxiety or other mood symptoms.3 When depression is investigated longitudinally in schizophrenia, the vast majority, up to 80%, of patients experience a clinically significant depressive episode at 1 or more time point during the early phase. This underlines how cross-sectional rates markedly underestimate the true prevalence and suggests that in the early phase of illness at least, mood symptoms may be more than "comorbid" experiences. The diversity in reported figures for depression is also partly attributed to the challenge in distinguishing mood symptoms from negative symptoms, suggesting a complex and as yet poorly understood overlap with other symptom dimensions at a phenomenological level. 4 Depression in schizophrenia has long been a taxonomic challenge leading to assertions that true schizophrenia is "non-affective"; or invention of new diagnoses and broadening definitions, such as schizoaffective disorder. In DSM-V schizoaffective disorder, the occurrence of the delusions or hallucinations must be present in the absence of any serious mood symptoms for at least 2 weeks whilst the mood disorder must be present for the majority of the total duration of illness.5 Our increasing knowledge as to the prevalence and course of depression in schizophrenia particularly, in the early years makes, the distinction between schizophrenia and new definitions of schizoaffective disorder even more challenging.