Has possibly the earliest onset compared to all other schizophrenias, considered to begin in some within childhood. Symptomatic of the simplex is an absence of will, impoverished thinking and flattening of affect. There is a gradual deterioration of functioning with increased amotivation and reduced socialization. It is considered to be rarely diagnosed and is a schizophrenia without psychotic symptoms (Mueser & Jeste 2008).
In a study of patients in a Massachusetts hospital; persons suffering with simple-schizophrenia were found to make attempts at reality fulfillment with respect to the more primitive needs; tending toward the achievement of fulfillment of these needs rather than engaging in fantasy as is typically found as a reaction to environmental stimuli by the psychotic person (Kant 1948).
|“||Slowly progressive development over a period of at least one year, of all three of the following: 1.(a) of loss of drive and interests,aimlessness, idleness,a self-absorbed attitude and social withdrawal that progress.(b) Gradual appearance and deepening of negative symptoms such as marked apathy, paucity of speech, underactivity, blunting of affect, passivity and lack of initiative, and poor non-verbal communication. (c) Marked decline in social, scholastic or occupational performance.
2. Absence, at any time, of any symptoms referred to in G1 in F20.0 - F20.3  and of hallucinations and well formed delusions of any kind....
3. Absence of evidence of dementia or any other organic disorder...
The only primary symptom is the withdrawal of the person from social and work related situations (Přikryl & Kučerová 2004) 
Definition of this type is without unity or is controversial, or else is within a divided opinion. The classification was discontinued in the U.S. DSM system, although recommended for reinclusion (Black & Boffeli 1989), was subsequently confirmed as having imprecise diagnostic criteria based on collective descriptions lacking in agreement (Black & Boffeli 1990).
In an experiment with a small sample size (five) persons having had a diagnosis of simple-type (DSM-IV simple deteriotive disorder) were found to have grey matter deficits, atrophy and reduced cerebral perfusion in the frontal areas (Suzuki 2005). Whitwell et al 2005 found justification to retain the classification on the basis of fulfillment of "dimensional" considerations of classification, as opposed to criticisms resulting from disagreement in considerations of classification using orientation from other categories.
A progressive state of simple dementia results often in cases of adolescent onset Juvenile general paresis. Paresis is being caused by placental-foetal transfer of infection and results in intellectual (mental) subnormality. Occurrence of this type of paresis is altogether uncommon (Lishman 1998).
History of definition
The early idea that a person with schizophrenia might present solely with symptoms and indications of deterioration ( i.e. in presentation having no accessory symptoms ) was identified as dementia simplex (Serra-Mestres et al 1997),
ICD-10 specifies the continuation of symptoms for a period of two years in the diagnosis of simple schizophrenia. This is because of disagreement on the classification validity of the sub-type, that having been retained by the ICD classification, has been omitted from DSM classifications.
Symptoms identified earlier to dementia simplex are now DSM-attributed by way of improvements in diagnostic technique to other classifications such as neurodegenerative disorders.
Early observations that concur with symptoms of the dementia praecox of the form classified later as simplex began in 1838  with Esquirol. Morel in 1860 introduced the term dementia précoce, Langdon Down in 1887 provided the most complete description to that date of the clinical manifestation that Charpentier described in 1890 as dementia précoce simple des enfant normaux (Pick 1924). The description simple schizophrenia is a description that is inter-changeable with describing symptoms as a form of dementia praecox known as simple dementing, at least in the time of Diem and Bleuler. Kraeplin in 1893 considered there were four types (Green 2009), was amongst the first to identify three types (hebephrenic, paranoid, simplex) of schizophrenia (Weinberger & Harrison 2011).This type was added by E Bleuler to the earlier Kraeplin four identified in 1899, and subsequently given a basic outline (Diem et al 1903), in 1903 by O. Diem publishing a monograph on dementia praecox in the simple dementing form. This was based on survey of two males having had a relatively normal childhood to then fall into patterns of living tending toward vagrancy.
A description of a cerebral disorder in relation to organic factors and in the context of general paralysis of the insane only; with no reference to schizophrenia,shows a disorder with features of generalized dementia (Lishman 1998).
In 1951 a film was made showing the clinical characteristics of chronic simple type.
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