Schizophrenia: Clinical Symptoms and Diagnostic Assessment A Review of Presentation, Diagnostic Criteria, and Differential Diagnosis

Schizophrenia is a severe and heterogeneous psychiatric disorder that typically emerges in late adolescence or early adulthood and affects roughly 1% of people over a lifetime. Because no validated biomarker exists, diagnosis rests on careful clinical assessment of a characteristic cluster of symptoms, their duration, associated functional decline, and the exclusion of other causes. This paper reviews the symptom domains of schizophrenia (positive, negative, disorganized, and cognitive), the typical course from the prodromal phase to chronic illness, and the diagnostic criteria set out in the DSM-5-TR and ICD-11. It also describes standard assessment instruments, outlines the main differential diagnoses, and discusses ongoing challenges, including early detection, cultural variation in presentation, and diagnostic overlap with mood and neurodevelopmental disorders. Improving the accuracy and timeliness of diagnosis remains central to reducing the long-term disability associated with the illness