Because of the great difficulty in obtaining information on the onset and early course of schizophrenia prospectively, due to the low incidence rate and a frequent onset with uncharacteristic symptoms, prodromal signs usually go unheeded when they appear. In traditional clinical settings, first contact with mental health services in most cases takes place during the first psychotic episode. Help-seeking is usually precipitated by a loss of working ability and the distress caused by psychosis to the sick person and his/her environment. In the ABC Schizophrenia Study the time span between onset of the first psychotic episode and first contact varied around a mean of 1.3 years (median 0.8 years).
Due to their obscurity, the prodromal symptoms of the first episode were also lacking or listed incompletely in the international classification systems and at first reconstructed on the basis of symptoms occurring in the further illness course .
Different attempts have been made to assess prepsychotic prodromal symptoms that do not usually come to clinical observation. Janzarik  and Gross , proceeding from clinical observation of residual symptoms in the psychosis-free interval in patients with long histories of illness, found above all negative symptoms and signs of functional impairment, at that time called a ''defect''. Presuming that prodromal and residual symptoms are identical, Janzarik concluded that there must be an ''anteceding defect state'' observable before the first psychotic episode, whereas Gross  and Huber et al.  spoke of ''basic symptoms'' which, unlike psychotic symptoms, are direct expressions of degenerative brain changes. Such prodromal symptoms also to be found among the residual symptoms include, for example, affective flattening, avolition, and difficulties of thinking and concentration .
This approach is in part well founded, because negative symptoms and functional impairment constitute the most stable symptom dimension in schizophrenia. As retrospective analyses have shown , they tend to emerge long before psychosis onset (see Table 1.1). Negative symptoms manifest themselves before and simultaneously with positive symptoms and reach a maximum at the climax of the psychotic episode. As the psychosis remits, they too remit fully or in part . In the further illness course, their prevalence shows a plateau . But prodromal symptoms are not limited to the negative symptoms and functional impairment observable at the residual stage. Affective, especially depressive, dysphoric and other ''unspecific'' symptoms and behavioural anomalies play an important role at the prepsychotic stage.
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