Validity of the Schizophrenia Diagnosis of the Psychiatric Assessment Schedule for Adults with Developmental Disability (PAS–ADD)

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Abstract
Background: First rank symptoms are central to the diagnosis of schizophrenia, but their complexity makes it difficult to validly detect them in people with learning disability. This report investigates ability of PAS–ADD to detect schizophrenia, validated against expert clinical opinion.Method: The sample consisted of 98 patients with learning disability, and a key informant for each sample member. Clinical opinions of the referring psychiatrists were sought using a symptom checklist. Reportage of remission, and the number of core schizophrenia symptoms identified, were used to estimate level of symptom activity at time of interview.Results: The proportion of schizophrenia cases detected by PAS–ADD increases with the number of active core symptoms identified by the referrer. Where two or more core symptoms were indicated, PAS–ADD detected 71 % cases. The most frequently fulfilled criterion was third-person auditory hallucinations. Six schizophrenia diagnoses disagreed with the clinician, four of which were referred as being hypomania. Overall symptom frequency detected by PAS–ADD was positively correlated with IQ.Conclusions: Results suggest there may be scope for modifying the ICD–10 diagnostic algorithm for use with learning disability, particularly in relation to the delusions and negative symptoms criteria.