For the depressive disorders, both ICD-10 and DSM-IV have multiple conditions and specifiers. The ICD-10 system allows mild and moderate depressive episodes (with or without a 'somatic syndrome' conceptualized as reflecting 'melancholic' features), and severe depressive episode (with or without psychotic symptoms). There are separate codes for a similar set of 'recurrent' disorders, while several 'persistent' mood disorders (including cyclothymia and dysthymia) and residual conditions are listed. DSM-IV has two principal 'stem' disorders (major depressive episode and dysthymia), with the first having a number of optional specifiers including 'with' melancholic, catatonic, psychotic, or atypical features, as well as including disorders showing longitudinal patterns of rapid cycling or a seasonal pattern. Both systems have categories for affective disorders secondary to organic disease, while DSM-IV includes mood disorders due to a general medical condition or substance use, or occurring in the post-partum period. Both classificatory systems include adjustment disorders with depression.
Both ICD-10 and DSM-IV have course specifiers for bipolar disorder containing 10 and four subgroups, respectively. In addition to the number of subgroups, differences include a greater emphasis on distinguishing bipolar I and II in DSM-IV, and cyclothymia being listed as a 'bipolar disorder' in DSM-IV as against being a 'persistent' mood disorder overlapping with a personality style in ICD-10.
For episode disorders, both systems list mania and hypomania, with ICD-10 favouring descriptive diagnostic criteria and DSM-IV specifying duration and required criterion numbers. ICD-10 allows manic subtypes with and without psychotic features, while DSM-IV puts little emphasis on psychotic features in its criterion set, although both favour a duration of at least a week. For hypomania, both DSM-IV and ICD-10 exclude those with psychotic features, and impose a minimum duration (4 days for DSM-IV and 'several days' for ICD-10). DSM-IV requires the presence of at least three specific features, while ICD-10 requires mood and behavioural features to be intermediate between cyclothymia and mania.
Formal classifications are therefore built principally on severity, features of current episode, patterns of disorder expression over time, as well as persistence and recurrence. Few diagnoses are consistent across the ICD-10 and DSM-IV systems and, while each provides definitions that allow a 'shared language' to be used by clinicians and researchers, the extent to which their severity-weighted groupings capture 'meaningful' depressive subtypes remains problematic.
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