The obsessive compulsive disorder (OCD) has as a neuro-biochemical under-layer an imbalance on multiple neuro-transmitter lines: serotinone, noradrenaline and Gama Amino Butiric Acid. In time, an imbalance appears in the balances serotonine/dopamine and noradrenaline/dopamine (noradrenaline modulates the activity of the dopaminergic system), generating dysfunctionality in the dopaminergic line. It creates thus the neurobiochemical support for the development of a psychotic board.

The specialized studies reveal the implication of 5 and 11 chromosomes both in schizophrenia and in OCD (genetic determinism). In this way the vulnerability through genetic support of the passage to psychotic pathology from OCD can be explained.

The imagistic modifications emphasized by PET and SPECT, at the level of the frontal lobe, of basal ganglia and cingular gyrus, in the two disorders as well as electroencephalographic modifications sometimes similar, emphasize the idea tha OCD can at time be a step towards the first psychotic episode in schizophrenia.

The anxiety within the OCD symptomatology can produce an aggression on the hypocampus, a mechanism present also in schizophrenia.

The highlighted data thereby explains the therapeutic response from some OCD forms to the treatment with second generation antipsychotics. Our clinical experience emphasized the fact that it is these forms that are resistant to standard therapy generally represent the entry to schizophrenia