Background: Two thirds of patients with obsessive-compulsive disorder (OCD) respond to treatment with selective serotonin reuptake inhibitors (SSRIs). The neurobiological mechanisms of SSRI action and failure to respond to SSRI treatment remain to be elucidated. Objectives: The aim of this pilot study was to quantify changes in the availability of serotonin transporter (SERT) in the course of SSRI treatment and to relate these changes to improvements of clinical symptoms. Methods: Ten patients with OCD were investigated at baseline and 5 of them after 1 year of SSRI treatment with citalopram 60 mg per day using brain single photon emission computed tomography and [123I]β-CIT. Specific-to-nondisplaceable [123I]β-CIT binding ratios (V3″) were calculated in SERT-rich brainstem, midbrain and thalamus using a magnetic resonance imaging-based region of interest (ROI) analysis. Symptom severity was evaluated with the Yale-Brown Obsessive-Compulsive Scale (Y-BOCS). Results: V3″ differed significantly between pretreatment and follow-up scans in all three brain regions, thalamus, midbrain as well as in brainstem. In thalamic ROI, differ ences in SERT availability and Y-BOCS ratings correlated. In midbrain, a trend toward a significant association was found. In brainstem, no relationship was revealed. Conclusions: Higher occupancy of SERT by citalopram seems to be associated with better clinical response after 1 year of SSRI treatment of patients with OCD.

Keywords:
Citalopram, β-CIT, Obsessive-compulsive disorder, Single photon emission computed tomography, Serotonin transporter
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© 2006 S. Karger AG, Basel
2006
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