RESUMO
Traditionally, schizophrenia is considered to be a result of dopaminergic hyperactivity while dopaminergic deficiency underlies Parkinson’s disease (PD). This opposing pathophysiology makes comorbid schizophrenia and PD seemingly impossible; however, they do coexist rarely in clinical practice. We present four patients with paranoid schizophrenia diagnosed in their youth who developed parkinsonian symptoms on a stable regimen of quetiapine or clozapine after several years. The diagnosis of comorbid schizophrenia and PD was made mainly according to clinical observation. In addition, dopamine transporter (DAT) imaging with 18F-FP-CIT PET was done in two patients, which showed normal DAT density. It is believed that dopaminergic dysfunction in distinct dopaminergic pathways may explain the coexistence of these two disorders