What are the key diagnostic differences between schizophrenia and schizoaffective disorder?
“Mr Piety” is a 34-year-old white male with a history of chronic schizoaffective disorder, bipolar type. He was stable on a regimen of clozapine 125 mg twice daily and valproic acid 1500 mg at bedtime for more than a decade. He was noted to have morbid obesity, with a body mass index of 50 kg/m2. Mr Piety reported a history of 1 lifetime manic episode lasting less than 2 weeks in his late teens. Otherwise, he denied a history of manic symptoms. He also denied significant depressive symptoms. He did not feel that the valproic acid was particularly helpful.
Mr Piety’s psychiatrist changed his diagnosis from schizoaffective disorder to schizophrenia and tapered him off valproic acid over a period of 3 to 4 months. Mr Piety did not experience recurrence of any mood symptoms and there were no other changes to his psychotropic medication regimen. One year later, he had lost 26 lbs (8% of his baseline total body weight) and his BMI was 45.7. Less than 4 years later, he had lost 48 lbs (16% of his baseline total body weight) and his BMI was 42.
Schizoaffective disorder has been a controversial diagnosis since its inception, first appearing in DSM-III.1,2 In DSM-III-R, schizoaffective disorder required the presence of affective symptoms for a “substantial” period (the definition of “substantial” was not further specified) relative to the total duration of illness, with a period of at least 2 weeks characterized by psychotic symptoms in the absence of affective symptoms.2
The prevalence of DSM-IV schizoaffective disorder was nontrivial.3 However, the diagnostic reliability of schizoaffective disorder is low relative to other differential diagnoses, and overdiagnosis has been a concern.4
As a result, in DSM-5, more stringent criteria for the diagnosis were introduced, requiring the presence of affective symptoms for a majority of the course of illness (Table).5
Many patients receive different diagnoses over time, including schizoaffective disorder, schizophrenia, and a mood disorder with psychotic features.4,6
The Current Study
Florentin and colleagues7 aimed to describe differences in demographic and hospitalization characteristics across different diagnostic groups, to compare the stability of the schizoaffective disorder diagnosis, and to assess changes in the incidence of schizoaffective disorder following changes to the diagnostic criteria in DSM-5.
The study authors extracted data from the national Psychiatric Case Registry from the Ministry of Health of Israel, which covers all psychiatric admissions and discharges in the country since 1950. They identified all psychiatric inpatients aged 18 to 65 years who had been hospitalized between 2010 and 2015 with a diagnosis of either schizophrenia or schizoaffective disorder on their last discharge. For each patient, all psychiatric diagnoses from hospitalizations between 1963 and 2017 were recorded. They included 16,341 patients with at least 2 hospitalizations during this period.
The authors trichotomized patients into diagnostic groups: (1) those who received a diagnosis only of schizophrenia, (2) those who received a diagnosis only of schizoaffective disorder, and (3) those with both diagnoses. These groups were compared based on age, sex, ethnicity, substance use disorder, total number of hospitalizations, and average length of stay.
Cohen’s κ coefficient was used to measure reliability between first vs last diagnosis and most frequent vs first and last diagnosis. They assessed “diagnostic constancy,” defined as the presence of the same diagnoses in more than 75% of hospitalizations. Logistic regression models were used to predict the stability between first and most frequent diagnosis.
In the study sample, 64.6% were schizophrenia only, 11.5% were schizoaffective only, and 23.9% had both diagnoses. Those with both diagnoses were older, had an earlier mean age at first hospitalization, had a higher prevalence of substance use disorder, and had a greater number of mean number of hospitalizations than those in the other 2 groups. The proportion of males was highest in the schizophrenia-only group.
Thirty-eight percent of patients with a first diagnosis of schizoaffective disorder subsequently received a diagnosis of schizophrenia, and 21% with a first diagnosis of schizophrenia subsequently received a diagnosis of schizoaffective disorder.
Overall, the κ (reliability) between the first and most frequent diagnosis was 0.71. With an increasing number of hospitalizations, the agreement between first and most frequent diagnosis decreased. There was little change in the proportion of patients who received a diagnosis of schizoaffective disorder at first hospitalization between the pre- and post-DSM-5 period (8.5% vs 10.7%).
The authors found that schizophrenia was 2.5 times more frequently diagnosed than schizoaffective disorder, which is similar to previous findings.3 The relative size of the schizoaffective-only group diminished with an increasing number of hospitalizations. Almost 40% of patients who first received a diagnosis of schizoaffective disorder subsequently received a diagnosis of schizophrenia.
Prospective diagnostic consistency was lower for schizoaffective disorder than for schizophrenia. The authors noted that the increased prevalence of substance use disorder comorbidity in the “both disorders” group may contribute to diagnostic instability. Finally, there was little chance in the incidence of schizoaffective disorder in the pre- vs post–DSM-5 period.
Study strengths included the large sample using a national case registry over a 50-year period and the unique approach to assessing diagnostic stability. The primary study limitation was the exclusion of patients with a last diagnosis of bipolar disorder. Other limitations included the retrospective design and the lack of availability of some clinical and prognostic factors.
The Bottom Line
The reliability of schizoaffective disorder is relatively low and its incidence has not decreased since the publication of DSM-5, despite stricter criteria.
Dr Miller is a professor in the Department of Psychiatry and Health Behavior at Augusta University in Augusta, Georgia. He is on the Editorial Board and serves as the schizophrenia section chief for Psychiatric Times®. The author reports that he receives research support from Augusta University, the National Institute of Mental Health, and the Stanley Medical Research Institute.
1. Maj M, Pirozzi R, Formicola AM, et al. Reliability and validity of the DSM-IV diagnostic category of schizoaffective disorder: preliminary data. J Affect Disord. 2000;57(1-3):95-98.
2. Diagnostic and Statistical Manual of Mental Disorders: DSM-3. 3rd ed. American Psychiatric Association; 1980.
3. Perälä J, Suvisaari J, Saarni SI, et al. Lifetime prevalence of psychotic and bipolar I disorders in a general population. Arch Gen Psychiatry. 2007;64(1):19-28.
4. Fusar-Poli P, Cappucciati M, Rutigliano G, et al. Diagnostic stability of ICD/DSM first episode psychosis diagnoses: meta-analysis. Schizophr Bull. 2016;42(6):1395-1406.
5. Diagnostic and Statistical Manual of Mental Disorders: DSM-5. 5th ed. American Psychiatric Association; 2013.
6. Bromet EJ, Kotov R, Fochtmann LJ, et al. Diagnostic shifts during the decade following first admission for psychosis. Am J Psychiatry. 2011;168(11):1186-1194.
7. Florentin S, Reuveni I, Rosca P, et al. Schizophrenia or schizoaffective disorder? A 50-year assessment of diagnostic stability based on a national case registry. Schizophr Res. 2023;252:110-117.