· Social/occupational dysfunction: For a significant portion of the time since the onset of the disturbance, one or more major areas of functioning such as work, interpersonal relations, or self-care, are markedly below the level achieved prior to the onset.
· Duration: Continuous signs of the disturbance persist for at least six months. This six-month period must include at least one month of symptoms (or less, if successfully treated).
Additional criteria are also given that exclude the diagnosis; thus schizophrenia cannot be diagnosed if symptoms of mood disorder or pervasive developmental disorder are present, or the symptoms are the direct result of a substance (e.g., abuse of a drug/medication) or a general medical condition.
Subtypes: Historically, schizophrenia in the West was classified into simple, catatonic, hebephrenic (now known as disorganized), and paranoid. The DSM contains five sub-classifications of schizophrenia:
· paranoid type: where delusions and hallucinations are present but thought disorder, disorganized behavior, and affective flattening are absent (DSM code 295.3/ICD code F20.0)
· disorganized type: named 'hebephrenic schizophrenia' in the ICD. Where thought disorder and flat affect are present together (DSM code 295.1/ICD code F20.1)
· catatonic type: prominent psychomotor disturbances are evident. Symptoms can include catatonic stupor and waxy flexibility (DSM code 295.2/ICD code F20.2)
· undifferentiated type: psychotic symptoms are present but the criteria for paranoid, disorganized, or catatonic types have not been met (DSM code 295.9/ICD code F20.3)
· residual type: where positive symptoms are present at a low intensity only (DSM code 295.6/ICD code F20.5)
The ICD-10 recognizes a further two subtypes:
· post-schizophrenic depression: a depressive episode arising in the aftermath of a schizophrenic illness where some low-level schizophrenic symptoms may still be present (ICD code F20.4)
simple schizophrenia: insidious but progressive development of prominent negative symptoms with no history of psychotic episodes (ICD code F20.6)
Diagnostic issues and controversies
Schizophrenia as a diagnostic entity has been criticized as lacking in scientific validity or reliability, part of a larger criticism of the validity of psychiatric diagnoses in general. One alternative suggests that the issues with the diagnosis would be better addressed as individual dimensions along which everyone varies, such that there is a spectrum or continuum rather than a cut-off between normal and ill. This approach appears consistent with research on schizotypy and of a relatively high prevalence of psychotic experiences and often non-distressing delusional beliefs amongst the general public.