LAUSR

Abstract Background Psychiatric disorders diagnoses are based on the satisfaction of specific symptoms criteria. Although this categorical method of classification, which is based on the identification of clinical syndromes, has proven useful in terms of treatment, its validity has been criticized. The possible symptoms combinations for major psychotic and mood disorder diagnoses could be calculated using combinatorial mathematics and the results could provide indices of diagnostic heterogeneity. Methods Our calculations were conducted using the binomial coefficient. In mathematics, this coefficient calculates the number of an unordered and unrepetitive selection of k items from a set S (a subset of k items from S) with the following formula: n!/k!(n-k)!. We calculated the possible number of combinations of symptoms required for diagnosing a) two major psychotic disorders (a1. Schizophrenia-SCZ and a2. schizoaffective disorder-SAD), and b) two major mood disorders-episodes (b1. Major Depressive Episode-MDE and b2. Manic Episode- ME), implementing the DSM-5 and DSM-IV diagnostic criteria. For each diagnosis, k corresponds to the number of the necessary symptoms, where S to the total number of symptoms described in the relevant criteria. The following calculations were conservative, since they did not take into account all the possible combinations within each criterion, the effect of specifiers or the effect of SCZ, or SAD subtypes. Results We found the following combinations: DSM-5: SCZ=25, SAD=12,225, MDE=163, ME=326. DSM-IV: SCZ=74, SAD=2,762,198, MDE=163, ME=163. According to DSM-IV (but not to DSM-5), Criterion A for Schizophrenia could coexist with a mixed mood episode in SAD. Interestingly, the possible symptoms combinations for a mixed episode was 37,001. The possible symptoms combinations for the diagnosis of schizophrenia has been slightly reduced in DSM-5 as compared with DSM-IV, but the reduction in the number of relevant combinations for the diagnosis of SAD has been impressive. This reduction was driven by the removal of mixed mood episodes in DSM-5. The possible combinations in SCZ, albeit not in SAD, were fewer than those required for the diagnosis of a MDE and a ME. Discussion The above results indicated that the diagnostic heterogeneity of psychotic disorders differed from that of mood disorders. SAD appeared to be the most heterogeneous disorder. DSM-5 criteria have limited the possible combinations of symptoms and have therefore improved the heterogeneity of SCZ and SAD, but not that of major mood disorders. The extent and the clinical implications of diagnostic heterogeneity in different psychotic and mood disorders remain to be elucidated by future research.