Direct structured interviews are reliable for assessing negative schizophrenia symptoms, but combining information from both direct interviews and medical records will reduce the risk of missing important positive symptoms, findings from the Irish Case-Control Study of Schizophrenia suggest.

An evaluation of the level of agreement between symptom ratings derived using direct structured interviews and by a review of case notes for 1,021 subjects with schizophrenia showed that 14 of 20 symptoms evaluated were significantly correlated for method of assessment, including all negative symptoms.

The six that did not correlate – thought insertion, thought withdrawal, somatic delusions, voices speaking in sentences, visual hallucinations, and somatic hallucinations – all were positive symptoms, Dr. Ayman H. Fanous of the Washington (D.C.) VA Medical Center and his colleagues reported in the April issue of Comprehensive Psychiatry (Compr. Psychiatry 2012;53:275-9).

Exploratory factor analysis using the mean of the interview and case note ratings for each symptom were used to examine the factor structure of signs and symptoms of psychotic illness in the sample. This identified three main factors: positive symptoms (including grandiose delusions, somatic delusions, religious delusions, visual hallucinations, and somatic hallucinations); negative symptoms (including affective flattening, alogia, avolition, anhedonia, attentional disturbance, inappropriate affect, and thought disorder); and Schneiderian symptoms (including thought insertion, thought withdrawal, thought broadcasting, voices discussing, and voices commenting).

“Of the 3 factors, negative symptoms clearly were most strongly correlated across method of assessment. All negative symptoms were significantly correlated, with a mean r of +0.34. This was followed by positive symptoms, with 2 of 5 symptoms significantly correlated and mean r of +0.27,” the investigators wrote. The least correlated factors across modes of assessment were the Schneiderian symptoms, with 3 of 5 significantly correlated and a mean r of +0.19, they noted.

The findings, which are among the first to assess correlation of symptom-assessment methods in schizophrenia, show that, for most symptoms, reasonable concordance exists between direct structured interviews and case notes review – particularly for negative symptoms, which are more stable over time and are directly observable and thus do not require a patient to divulge thought content.

The positive symptoms that did not correlate across assessment method (including two classic Schneiderian delusions – thought insertion and thought withdrawal) reflect delusional or hallucinatory experiences that would require the patients to divulge their presence to an interviewer and are thus likely to be underreported.

These symptoms also might go undetected for other reasons, such as less frequent probing about them by clinicians, inadequacy of interview phraseology for capturing the experience of the symptoms for some patients, and difficulty with the abstract thinking needed to convey some of the symptoms as concepts, Dr. Fanous and his associates said.

“Overall, our results suggest that single sources of information may have a significant risk of missing important positive symptoms such as Schneiderian delusions and hallucinations, as well as less prevalent positive symptoms such as somatic hallucinations,” the investigators said, adding that the findings highlight the importance of combining information from chart review and informant interview, as well as case notes.

Participants in the Irish Case-Control Study of Schizophrenia were enrolled from inpatient and outpatient psychiatric facilities in the Republic of Ireland and Northern Ireland. All had a diagnosis of schizophrenia or poor-outcome schizoaffective disorder by DSM-III-R criteria. “This was done to maintain consistency with our previous studies in this population,” they wrote.

All of the participants also were assessed using a modified version of the Structured Clinical Interview for DSM-III-R. Symptom ratings were derived from the interview by the interviewer, who assessed the severity of all symptoms. Case notes were reviewed by a specially trained rater who reviewed case records, including admission mental status and discharge summaries as well as scanned psychiatrists’ and nurses’ progress notes, and who rated case notes using the Casenote Rating Scale.

Dr. Fanous was supported by a grant from the Department of Veterans Affairs Merit Review Program. Dr. Kenneth S. Kendler, another author of the study, was supported by grants from the National Institute of Mental Health