Psychotic depression now fulfills the criteria for a valid psychiatric syndrome

The number of studies reporting significant and clinically relevant differences between psychotic depression (PD) and non-PD has increased considerably over the past decades. This summary of the current evidence suggests that PD now fulfills the criteria for a valid psychiatric syndrome.

The suggested redefinition of PD in the ICD-11 is merited and such a revision will be of benefit to both research and clinical practice.

In the current issue of Psychotherapy and Psychosomatics, a group of Danish investigators is presenting data that support a new classification of psychotic depression. Depression accompanied by psychotic symptoms is referred to as delusional or psychotic depression (PD). PD is prevalent, underdiagnosed, undertreated and has a high morbidity and mortality, but has received disproportionally little attention compared with other less prevalent and less severe mental disorders.

Based on the detection of a number of biological, clinical, therapeutic and prognostic differences between PD and non-psychotic depression (non-PD), it was proposed that psychotic depression should be categorized as a distinct syndrome in the DSM-IV. This paper deals with the arguments in favour of and against classifying PD as a distinct syndrome under the affective disorders. Finally, based on this evaluation of the current evidence, the investigators give an outline for a redefinition of PD for the upcoming 11th revision of the International Classification of Disease (ICD-11), which is due in 2015. PD is characterized by the presence of delusions and/ or hallucinations in addition to depression.

A typical case is a patient displaying anhedonia, psychomotor retardation, loss of interest, poor concentration and who is tormented by delusions of guilt, disease, worthlessness or impending disaster. PD has a characteristic symptomatology which, apart from the psychotic features, involves a psychomotor disturbance (either agitation or retardation), rumination, insomnia, cognitive dysfunction and perplexity more often than non-PD. Regarding the course of disease, PD is associated with increased long-term psychosocial impairment, increased rates of relapse and higher levels of mortality compared to non-PD, possibly due to increased risk of suicide.

One of the arguments raised by the DSM-IV Work Group on Mood Disorders against the classification of PD as a distinct entity was that the number of psychiatric syndromes was already too high, but since PD is a rather prevalent disorder and already defined in the diagnostic manuals, this argument seems misplaced in the discussion of defining PD as a distinct diagnostic syndrome. Another counterpoint to PD being a distinct syndrome concerns the relationship between the severity of depression and the presence of psychosis. It has been suggested that the differences between PD and non-PD could reflect mere differences in depressive severity.

However, recent findings have demonstrated that episodes of PD are not necessarily 'severe' according to the number of depressive symptoms and that patients without any history of psychosis may experience nonpsychotic depressive episodes of greater symptom severity compared to psychotic depressive episodes in patients with PD. Another counterpoint to PD being a distinct syndrome concerns the stability of the diagnosis. A very recent study has caused reason to question the validity of PD due to its finding of low diagnostic stability over 10 Years.

However, changes in diagnoses over time and so-called diagnostic drift exists for all mental disorders and for virtually all diseases in general. Depression is heritable, but among the less heritable of the mental disorders, where schizophrenia and bipolar disorder lie at the other end of the spectrum. However, studies have indicated that the heritability of PD is stronger than that of non-PD and that PD displays considerable specificity in familial transmission.

Another argument against the separation of PD from non-PD raised by the DSM-IV Work Group concerned the response to treatment. The general opinion remains that PD responds poorly to antidepressant monotherapy and there is even some evidence suggesting that this regimen can exacerbate the psychotic dimension of the disorder. There is a growing body of evidence from recent randomized controlled trials, suggesting that the combination of an antidepressant and an antipsychotic is the superior pharmacological treatment approach in patients with PD. In agreement with these findings, most major expert guidelines on PD recommend either electroconvulsive therapy or the combination of an antidepressant and an antipsychotic as first-line treatment.

This recommendation differs significantly from those for non-PD, where the augmentation with antipsychotics is generally reserved for depression resistant to at least two trials with antidepressant monotherapy. Patients with unipolar psychotic depression (UPD) are at high risk of converting to bipolar disorder, relatives of patients with UPD have higher prevalence of bipolar disorder compared to relatives of patients with non-PD and unipolar depressed relatives of patients with bipolar disorders are more likely to suffer from the psychotic subtype than are unipolar depressed relatives of healthy controls.

However, equivalent to the case of UPD, it appears that the psychotic subtype of bipolar depression may also have implications for the symptomatology, treatment response, course of illness and prognosis. PD fulfils the criteria for a valid psychiatric syndrome due to its distinct clinical presentation, neurobiology, heritability, prognosis and treatment response. The investigators believe that the suggested redefinition of PD in the ICD-11 is merited and that such a revision will be of benefit to both research and clinical practice. The suggested modification allows the definition of a useful 'meta-syndrome' entitled 'psychotic depression' across the affective disorder chapter.