Over 10 years, 41 percent of patients initially diagnosed with delusional disorder transitioned to schizophrenia, a 10-year prospective comparison study in Hong Kong has shown. The results also showed a lower burden of adverse clinical outcomes with stable delusional disorder compared with stable schizophrenia.
“To our knowledge, this is the first prospective decade-long follow-up comparing diagnostic stability and long-term clinical, functional, and cognitive outcomes between delusional disorder [mean age, 42.76 years; male, 50 percent] and schizophrenia [mean age, 40.96 years; male, 42 percent] in an age-matched first-episode psychosis cohort,” noted researchers from the University of Hong Kong (HKU). [Schizophr Bull 2026;doi:10.1093/schbul/sbag145]
Less diagnostic stability with delusional disorder
Over 10 years, 41 percent (n=29/71) of patients initially diagnosed with delusional disorder transitioned to schizophrenia. Among those initially diagnosed with schizophrenia, only 3 percent (n=2/71) transitioned to schizoaffective disorder.
“The marked transition from delusional disorder to schizophrenia over the decade corroborates evidence that delusional disorder is less diagnostically stable than schizophrenia, and cautions against viewing delusional disorder as a wholly distinct diagnostic entity,” commented the researchers.
Selected outcomes differ at 10 years
As diagnostic stability alone cannot determine whether delusional disorder and schizophrenia represent separate disorders or different expressions of a broader psychosis spectrum, the researchers compared long-term outcome patterns alongside diagnostic trajectories.
Ten-year clinical, functional, and cognitive outcomes were then compared among patients who retained their original diagnosis from baseline to the 10-year follow-up (n=111).
While long-term functional and cognitive outcomes were broadly comparable between diagnostically stable delusional disorder and schizophrenia at 10 years, differences emerged in selected clinical outcomes.
Specifically, patients with schizophrenia experienced more relapse (B, 1.27; 95 percent confidence interval [CI], 0.29–2.25; p=0.012), more severe hallucinations (B, 3.35; 95 percent CI, 0.77–5.92; p=0.012), and a marginally higher frequency of hospitalizations (B, 0.47; 95 percent CI, 0.0002–0.94; p=0.05). Moreover, patients with schizophrenia made more perseverative errors on the modified Wisconsin Card Sorting Test (B=4.31; 95 percent CI, 0.21–8.41; p=0.04), indicating poorer executive functioning.
“These findings emphasize that while relapse is common in psychosis, patients with schizophrenia face a substantially greater burden of relapse and hospitalization,” commented the researchers. “Targeted relapse-prevention strategies and sustained support may therefore be critical to improving outcomes for patients with schizophrenia.”
Patients with delusional disorder showed poorer insight, as demonstrated by higher total scores on the Scale to Assess Unawareness of Mental Disorder (B, -1.38; 95 percent CI, -2.20 to -0.55; p=0.002), which was consistent with previous reports. [Schizophr Bull 2026;doi:10.1093/schbul/sbag145; BMC Psychiatry 2023;23:676; Can J Psychiatr 2017;63:12-19] “This likely reflects the defining phenomenology of delusional disorder, characterized by strongly held systematized delusions that impair recognition of mental illness despite relatively preserved functioning,” explained the researchers.
Additionally, sensitivity analyses yielded comparable results, supporting the robustness of these findings.
“Taken together, these findings point to a psychosis-spectrum model of delusional disorder and schizophrenia, while emphasizing that the disorders remain clinically distinguishable and require diagnosis-sensitive assessment and treatment planning,” noted the researchers.