A person diagnosed with schizophrenia may demonstrate auditory hallucinations, delusions, and disorganized and unusual thinking and speech; this may range from loss of train of thought and subject flow, with sentences only loosely connected in meaning, to incoherence, known as word salad, in severe cases. Social isolation commonly occurs for a variety of reasons. Impairment in social cognition is associated with schizophrenia, as are symptoms of paranoia from delusions and hallucinations, and the negative symptoms of avolition (apathy or lack of motivation). In one uncommon subtype, the person may be largely mute, remain motionless in bizarre postures, or exhibit purposeless agitation; these are signs of catatonia. No one sign is diagnostic of schizophrenia, and all can occur in other medical and psychiatric conditions. The current classification of psychoses holds that symptoms need to have been present for at least one month in a period of at least six months of disturbed functioning. A schizophrenia-like psychosis of shorter duration is termed a schizophreniform disorder.
Late adolescence and early adulthood are peak years for the onset of schizophrenia. In 40% of men and 23% of women diagnosed with schizophrenia, the condition arose before the age of 19. These are critical periods in a young adult's social and vocational development, and they can be severely disrupted. To minimize the effect of schizophrenia, much work has recently been done to identify and treat the prodromal (pre-onset) phase of the illness, which has been detected up to 30 months before the onset of symptoms, but may be present longer. Those who go on to develop schizophrenia may experience the non-specific symptoms of social withdrawal, irritability and dysphoria in the prodromal period, and transient or self-limiting psychotic symptoms in the prodromal phase before psychosis becomes apparent.
The psychiatrist Kurt Schneider (1887–1967) listed the forms of psychotic symptoms that he thought distinguished schizophrenia from other psychotic disorders. These are called first-rank symptoms or Schneider's first-rank symptoms, and they include delusions of being controlled by an external force; the belief that thoughts are being inserted into or withdrawn from one's conscious mind; the belief that one's thoughts are being broadcast to other people; and hearing hallucinatory voices that comment on one's thoughts or actions or that have a conversation with other hallucinated voices. Although they have significantly contributed to the current diagnostic criteria, the specificity of first-rank symptoms has been questioned. A review of the diagnostic studies conducted between 1970 and 2005 found that these studies allow neither a reconfirmation nor a rejection of Schneider's claims, and suggested that first-rank symptoms be de-emphasized in future revisions of diagnostic systems.
Positive and Negative Symptoms
Schizophrenia is often described in terms of positive and negative (or deficit) symptoms. The term positive symptoms refers to symptoms that most individuals do not normally experience. They include delusions, auditory hallucinations, and thought disorder, and are typically regarded as manifestations of psychosis. Negative symptoms are so-named because they are considered to be the loss or absence of normal traits or abilities, and include features such as flat or blunted affect and emotion, poverty of speech (alogia), inability to experience pleasure (anhedonia), lack of desire to form relationships (asociality), and lack of motivation (avolition). Research suggests that negative symptoms contribute more to poor quality of life, functional disability, and the burden on others than do positive symptoms.
Despite the appearance of blunted affect, recent studies indicate that there is often a normal or even heightened level of emotionality in schizophrenia, especially in response to stressful or negative events. A third symptom grouping, the disorganization syndrome, is commonly described, and includes chaotic speech, thought, and behavior. There is evidence for a number of other symptom classifications.