Drug-Induced Parkinsonism or Parkinson's Disease: A Diagnostic Challenge in a Psychiatric Patient

Drug-induced parkinsonism (DIP) is the second most common cause of parkinsonian syndromes after idiopathic Parkinson's disease (iPD), accounting for approximately 15-25% of cases in older adults. While DIP typically results from antipsychotic-induced dopamine receptor blockade and is often reversible, iPD is a progressive neurodegenerative disorder characterized by asymmetrical onset, resting tremor, and good response to levodopa. Distinguishing between these conditions is clinically important but often challenging. The aim of this article is to discuss the diagnostic and therapeutic challenges involved in differentiating DIP from iPD in patients with psychiatric disorders who are chronically treated with antipsychotics. Based on the case of a 52-year-old man with a long-standing history of schizophrenia treatment, the diagnostic process and clinical manifestations leading to the final diagnosis are presented. The patient developed Parkinsonian symptoms during olanzapine therapy, initially suggesting DIP. This paper discusses the clinical indicators differentiating DIP from iPD, as well as the critical role of single photon emission computed tomography (SPECT) with ioflupane-123 (DaTSCAN) in the differential diagnosis of Parkinsonism in selected, ambiguous cases. The described case illustrates the phenomenon of so-called "unmasked Parkinson's disease" and highlights the need for detailed neurological monitoring in patients suspected of having DIP. It is essential to consider iPD as an independent cause of movement disorders in patients treated with antipsychotics. Early diagnosis and appropriate treatment of the underlying cause of Parkinsonism can significantly reduce extrapyramidal symptoms and improve the patient's quality of life.