The undifferentiated subtype is diagnosed when people have symptoms of schizophrenia that are not sufficiently formed or specific enough to permit classification of the illness into one of the other subtypes.
The symptoms of any one person can fluctuate at different points in time, resulting in uncertainty as to the correct subtype classification. Other people will exhibit symptoms that are remarkably stable over time but still may not fit one of the typical subtype pictures. In either instance, diagnosis of the undifferentiated subtype may best describe the mixed clinical syndrome.
How Is It Diagnosed?
Undifferentiated schizophrenia is a difficult diagnosis to make with any confidence because it depends on establishing the slowly progressive development of the characteristic “negative” symptoms of schizophrenia without any history of hallucinations, delusions, or other manifestations of an earlier psychotic episode, and with significant changes in personal behaviour, manifest as a marked loss of interest, idleness, and social withdrawal.
Bengston, M. (2013). Undifferentiated Schizophrenia. Psych Central. Retrieved on October 7, 2015, from http://psychcentral.com/lib/undifferentiated-schizophrenia/