RT Journal A1 Gilbert AR, Moore GJ, Keshavan MS, et al T1 DEcrease in thalamic volumes of pediatric patients with obsessive-compulsive disorder who are taking paroxetine JF Archives of General Psychiatry JO Archives of General Psychiatry YR 2000 FD May 1 VO 57 IS 5 SP 449 OP 456 DO 10.1001/archpsyc.57.5.449 UL http://dx.doi.org/10.1001/archpsyc.57.5.449 AB Background  Thalamic dysfunction has been implicated in obsessive-compulsive disorder (OCD). While OCD frequently has its onset during childhood, to our knowledge, no prior study has measured neuroanatomical changes in the thalamus of patients with OCD near the onset of illness, and before and after treatment.Methods  Volumetric magnetic resonance imaging studies were conducted in 21 psychotropic drug-naïve children, aged 8 to 17 years, with OCD and 21 case-matched healthy comparison subjects. Magnetic resonance imaging studies were also conducted in 10 of the 21 patients with OCD after 12 weeks of monotherapy with the selective serotonin reuptake inhibitor, paroxetine hydrochloride.Results  Thalamic volumes were significantly greater in treatment-naïve patients with OCD than in controls but declined significantly after paroxetine monotherapy to levels comparable with those of controls. Decrease in thalamic volume in patients with OCD was associated with reduction in OCD symptom severity.Conclusions  Our findings provide new evidence of thalamic abnormalities in pediatric OCD and further suggest that paroxetine treatment may be paralleled by a reduction in thalamic volume. These reductions may, however, not be specific to paroxetine treatment and could be due to a more general treatment response, and/or spontaneous improvement in symptoms. Our findings are preliminary given the small sample size and our inability to measure discrete thalamic nuclei.