Differential Diagnosis

The signs and symptoms that define schizophrenia may occur in the course of any disease affecting the brain, including a range of mental disorders, substance-induced disorders and general medical conditions.

The redefinition of the boundaries between schizophrenia and mood disorders, either manic or depressive, with psychotic symptoms, has been one of the most important changes in psychiatric nosology during the last two decades. Jaspers' hierarchical rule, according to which priority was to be given to a diagnosis of schizophrenia when both affective and schizophrenic symptoms were present, was abandoned and new rules were adopted to separate the two disorders.

The presence, at the same time, of a manic or depressive episode and mood-incongruent psychotic features, can be conceptualized in three different ways [86- 88]: as forming a particular subtype of a mood disorder, that is, mood incongruent psychotic affective illness (MICPAI); as defining a form of schizoaffective disorder; or as belonging to schizophrenia. In the DSM-IV Sourcebook, Kendler [88] has evaluated the three hypotheses regarding the nosologic position of MICPAI. According to this author, the accumulated evidence concerning antecedent validators (family history, demographics) as well as concurrent validators (clinical and biological variables, treatment response and outcome) supports the first hypothesis, that is, MICPAI should be considered a subtype of mood disorder.

The new rules that were adopted to separate schizophrenia from mood disorder also redefined the diagnosis of schizoaffective disorder. The current evidence concerning the status of schizoaffective disorder has been reviewed by Tsuang et al [89]. In the ''necessarily provisional view'' of the authors, schizoaffective disorder is ''a genetically heterogeneous condition primarily composed of schizophrenia, unipolar and bipolar disorders and perhaps a residual currently undifferentiated condition''.

A considerable number of labels and definitions have been proposed during the last century to designate transient psychotic disorders that are regarded as separate from schizophrenia. Prominent traditional concepts in this field are the bouffées délirantes of the French, the reactive or psychogenic psychoses as well as the schizophreniform psychoses of the Scandinavian, and the cycloid psychoses of the German tradition. Although it remains unclear whether transient psychotic disorders are different from schizophrenia, current classification systems have introduced various categories that allow sufficient time for the symptoms to appear, be recognized, and subside, before a diagnosis of schizophrenia can be made [90].

Since the days of Kraepelin, a number of persistent delusional disorders have been regarded as different from schizophrenia. The group includes a variety of conditions in which long-standing delusions constitute the only, or the most conspicuous, clinical characteristic and which do not meet criteria for a diagnosis of schizophrenia. Prominent in this area are the concepts of paranoia and paraphrenia, the délires chroniques of the French tradition, as well as a variety of other concepts, either included in the preceding or separated from them, such as delusional jealousy, folie à deux, Capgras syndrome, erotomania, Cotard's syndrome, or Kretschmer's sensitiver Beziehungswahn. The nosologic position of this group, in particular with regard to schizophrenia, remains uncertain [90].

Schizophrenia spectrum disorders include paranoid, schizoid and schizo-typal personality disorder. According to Siever et al [91], patients with schizotypal personality disorder demonstrate psychophysiological and cognitive deficits that are similar to, but milder than, those found in schizophrenia. In addition, the symptoms of schizotypal personality disorder seem to be heritable and genetically related to schizophrenia, but there is considerable overlap between schizotypal symptoms and symptoms of personality disorders that are outside the schizophrenia spectrum.

Schizophrenic signs and symptoms may occur in many medical or neurological conditions. Psychotic disorder due to a general medical condition must be excluded when making the diagnosis of schizophrenia.

The causal link between psychoactive substances and an episode of psychosis must also be excluded. The relationship between schizophrenia and substance-induced psychotic disorders may, however, sometimes remain uncertain.

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