Decrease in thalamic volumes of pediatric patients with obsessive-compulsive disorder who are taking paroxetine

Background: Thalamic dysfunction has been implicated. In obsessive-compulsi ve disorder (OCD). While OCD frequently has its onset during childhood, to our knowledge, no prior study has measured neuroanatomical changes in the t halamus of patients with OCD near the onset of illness, and before and afte r treatment. Methods: Volumetric magnetic resonance imaging studies were conducted in 21 psychotropic drug-naive children. aged 8 to 17 years, with OCD and 21 case -matched healthy comparison subjects. Magnetic resonance imaging studies we re also conducted in 10 of the 21 patients with OCD after 12 weeks of monot herapy with the selective serotonin reuptake inhibitor, paroxetine hydrochl oride. Results: Thalamic volumes were significantly greater in treatment-naive pat ients with OCD than in controls but declined significantly after paroxetine monotherapy to levels comparable with those of controls. Decrease in thala mic volume in patients with OCD was associated with reduction in OCD sympto m severity. Conclusions: Our findings provide new evidence of thalamic abnormalities in pediatric OCD and further suggest that paroxetine treatment may be paralle led by a reduction in thalamic volume. These reductions may, however, not b e specific to paroxetine treatment and could be due to a more general treat ment response, and/or spontaneous improvement in symptoms. Our findings are preliminary given the small sample size and our inability to measure discr ete thalamic nuclei.