A 24-year-old man has severe OCD refractory to two adequate SSRI trials. He is started on fluvoxamine augmented with risperidone. The rationale for adding an antipsychotic to an SSRI in OCD is:
- A Antipsychotics block D2 receptors in the striatum, augmenting the anti-obsessional SSRI effect via cortico-striato-thalamo-cortical (CSTC) circuit modulation ✓
- B Antipsychotics reduce serotonin synthesis, potentiating SSRI action by preventing serotonin autoreceptor downregulation
- C Risperidone converts serotonin to dopamine, directly enhancing OFC activity
- D Antipsychotics block GABA-B receptors in the thalamus, breaking the obsessive thought loop
Correct answer: A. Antipsychotics block D2 receptors in the striatum, augmenting the anti-obsessional SSRI effect via cortico-striato-thalamo-cortical (CSTC) circuit modulation
Explanation
OCD is neurobiologically linked to hyperactivity of the cortico-striato-thalamo-cortical (CSTC) circuit, particularly the orbitofrontal cortex-striatum-thalamus loop. SSRIs reduce serotonin-mediated OFC hyperactivity, while augmentation with low-dose atypical antipsychotics (haloperidol in tic-related OCD; risperidone, olanzapine in treatment-resistant cases) provides additional D2/D3 striatal modulation, normalising the circuit. This augmentation is evidence-based for SSRI-refractory OCD.
Reference: Kaplan & Sadock's Synopsis of Psychiatry, 11th ed.
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