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Unlabelled: The interferon alpha stands as a reference both in oncology and virology. But its efficiency is limited by frequent somatic as well as neuropsychic side effects. As a matter of fact, the reduction or the ending of a chemotherapy treatment come chiefly from the psychiatric complications caused by the use of interferon. For about 30% of patients, various psychic disorders are noticed: personality disorders, mood disorders, anxiety states, suicidal tendencies, manic and psychotic symptoms. We thus propose a review which shall be completed by a discussion on wether the interferon is responsible or not of the appearance of the described mental disorders. We shall conclude with a synthesis of the proposed practical management when confronted with such disorders. Psychiatric complications under interferon-Alpha. The appearance of psychiatric complications caused by interferon has been the subject of many publications. They have also raised the question of the toxicity mechanism which is still misunderstood today. This toxicity appears to be dose-dependent with variations depending on the daily dose given, the mode of administration, the combination with other chemotherapy treatments, the concomitance with a cerebral radiotherapy or a medical history of psychiatric disorders. Most of these effects occur after three weeks of treatment but non specific neuropsychic symptoms can be observed earlier. Non specific symptoms. They appear early but are difficult to detect, though they bring together a whole lot of clinical signs: asthenia, irritability, psychomotor slowdown, depressive mood or even a real "subsyndromic" depressive syndrome, anorexia, decline of the libido, concentration and attention problems, dizzy spells and headaches. Some authors have described intense and fluctuating of personality, mixing anxiety, irritability and disorder of drive control. Depression. Depression is the most frequently found psychiatric pathology in studies but the real frequency of clear cases of depressive problems is difficult to determine through lack of serious studies. So the incidence of depressive disorders usually varies from 5 to 15%. The depressive syndrome can settle as soon as the first week treatment, with a peak in the frequency during the first and third months. The seriousness and the incidence of this syndrome seem to be dose-dependent. The gravity of this complication lies in the suicidal risk, a risk all the more dreadful since there is not any identified risk factor. Suicides and suicidal behaviours. Serious complications, because they act directly on the vital prognosis. However fortunately, suicidal behaviours only represent a minority within all the side effects attributed to the interferon-alpha. These actions fit into three main clinical dimensions: complication of a severe depressive syndrome, confusional context and disorder of the impulses control. In practical terms, prevention proves to be difficult without identified predictive factors. Nevertheless, some authors point out the importance of aggravating comorbid disorders like alcoholism or the coinfection by the HIV. Manic syndrome. The appearance of a manic state under a chemotherapy treatment seems to be rare, given that there have been only a dozen cases published around the world. But these observations are interesting as far as both the study of imputability and the understanding of the toxicity mechanisms are concerned. Most of the cases deal with patients without a family or personal history of psychiatric disorders, and whose symptomatology disappears with the end of the treatment, which is an argument in favour of the imputation of the interferon in the appearance of manic disorders. In addition, some authors introduce the notion of tertiary mania: the appearance of an autoimmune hypothyroidism in relation with interferon and leading to athymic elation. Eventually, the appearance of manic problems at the end of the treatment makes it possible to speculate about the physiopathological mechanisms that are at issue. Anxiety disorders. These disorders are not much described: they generally are already existing disorders (like phobic or obsessive compulsive disorders), reactivated or aggravated by the interferon-alpha molecule. Adaptation disorders. It deals with adaptation disorders along with anxious temper coming at the beginning of the treatment. These problems are more concerned with the announcement of the diagnosis and its seriousness than with the toxicity of the interferon-alpha molecule. Psychotic states. There are less papers on the prevalence of psychotic disorders during the treatment, or at the end of it. But they can be found in both viral and malignant pathologies. A large retrospective study has shown ten cases of psychotic disorders and that in the absence of history of psychiatry or of a HIV co-infection. In every case the psychiatric aspect is stopped by the ending of the treatment or by an appropriated treatment. Usually, the few cases of paranoïd delusion described in papers seem to appear between one and three months of treatment, with patients having a history of psychiatric disorders. Aggravation of pre-existing mental disorders. Numerous authors have reported the recurrence of addictive behaviours (alcohol or other psychoactive matter) by weaned patients. Imputability to interferon-alpha in psychiatric disorders. It is difficult to draw the relationship between the chemotherapy with the interferon-alpha treatment and neuropsychiatric complications because there is a lack in specific studies. Nevertheless, it seems to be causal relations between the prescription of interferon and the appearance of psychic disorders. As a matter of fact, even if there is neither predictive criterion nor diagnosis of clinical type (set apart a dose effect), it is clear that there are diagnostic criteria of chronological kind: delay of appearance and disappearance of side effects compatible with the kinetics of the molecule and test of positive reintroduction. The imputability is thus most likely towards, given the reported clinical observations and signs of direct cerebral toxicity described for interferon: induction of neurophysiological changes among healthy volunteers, reversible EEG impairments the second week of treatment, direct vascular and neurological toxicity. Eventually, authors have shown that the psychiatric morbidity could be more important among patients under treatment than in a control group. In conclusion, the imputability of interferon appears to be very likely, more particularly in the appearance of mood disorders, mainly depressive ones, of manic syndromes and of certain psychotic episodes., Management: The most numerous therapeutic propositions naturally concern the depressive syndromes, because of their high frequency. In a recent article, the authors have detailed the pharmacological criteria of the ideal molecule: limited hepatic metabolism, low rate of proteinic fixation, long half-life and absence of active metabolite. So they advise not to prescribe imipraminic molecules and recommend the use of some SRI in first intention: citalopram and sertraline mainly, paroxetine to avoid given its pharmacological features that do not seem adapted. Only the minalcipram seems to show all the theoretical advantages described above. If there is an indication in the introduction of an anxiolytic medication, we shall prefer a benzodiazepine with short half-life like loxazepam and alprazolam. Besides, all the publications point out the importance of a specific clinical observation during the treatment as well as in the six months following its end. The agreement must bear full medical costs, above all including psychotherapic and social aspects. The proposed treatments for the other disorders are conventional: haloperidol and lithium for bipolar disorders, fluvoxamine for obsessive compulsive disorders and neuroleptics for psychotic disorders., Conclusion: The appearance of neuropsychiatric side effects during a chemotherapy using the interferon-alpha molecule is a frequent complication, the consequences of which can prove tragic: involvement of the vital prognosis, family and professional relation disturbances, compliance problems, risks of psychiatric morbidity at short and middle terms.... In spite of the absence of rigorous controlled studies, the imputability to the interferon of the appearance of psychological disorders appears very likely. So the role of the psychiatrist seems to be determining in the follow-up care of these patients who must be considered at high risk to develop a psychiatric pathology. The agreement to bear medical costs has to be made in narrow collaboration with clinical practitioners and must be part of a clinical continuity, from the pre-therapeutical evaluation to the remote follow-up care. Finally, it seems important to implement controlled studies, resting on a great diagnostic and methodological rigour, in order to clarify the toxicity mechanisms of interferon and to optimise the agreement to bear medical cost for the patients.