Negative symptoms are sometimes assumed to be specific to schizophrenia, but in fact they are not. This paper examines the frequency of negative symptoms in schizophrenia, mania, and major depression and indicates that both positive and negative symptoms may occur in all three. Clinicians judge these disorders to be present, not by observing a single pathognomonic symptom or group of symptoms, but rather by a process of pattern recognition of the characteristic clustering of symptoms. In addition to being diagnostically nonspecific, negative symptoms can also be produced by a broad range of factors, including positive symptoms, depression, and neuroleptic drugs. Research attempting to determine whether negative symptoms are treatment-refractory or treatment-responsive must take these factors into account.
