[Obsessive-compulsive disorder and depression]

Obsessive-compulsive disorders (OCD) are unique among the anxiety disorders. They have many characteristics in common with depressive disorders, both from clinical as well from psychopathological and neurochemical perspectives. The clinical response to serotonergic antidepressants is also similar. But, in spite of the common aspects, there are at every level important peculiarities which definitively differentiate OCD from depressive disorders. We present data on neuroendocrinological challenges and on brain regional blood flow measured with the SPECT. OCD patients not fulfilling diagnostic criteria for depression have an exaggerated response to a serotonergic challenge, measured by the increase in Prl, Cor and GH plasma concentrations when compared to controls. The differences are higher when controlling for the presence of depressive (subsyndromal) symptoms. Patients with OCD and comorbid depression have a blunted response to the CMI challenge. SPECT shows an increased blood flow in basal ganglia and hippocampus on the left side. In the presence of a comorbid depression, the regional brain blood flow shows a marked decrease in wide range of brain regions. Therefore, the presence of depressive symptoms and even more of diagnostic criteria for major depression significantly changes neuroendocrinological challenge tests and regional blood flow in OCD patients, making them look like depressive patients. Although depressive symptoms are present in many OCD patients and that there is a significant comorbidity between OCD and depressive disorders, we believe that they can be differentiated from the biological point of view. Furthermore, the association of depressive symptoms and of depression diagnostic criteria to OCD masks the biological finding, neurochemical and of brin regional blood flow, of OCD. This is an important factor to be considered when carrying out research in this field.