Diagnostic instability of recurrence and the impact on recurrence rates in depressive and anxiety disorders.

Background: Despite increasing evidence for the diagnostic instability between and within depressive and anxiety disorders, most studies report solely on the recurrence rates of the specific index disorders. Neglecting this evidence has an inherent risk of underestimating recurrence rates of depressive and anxiety disorders. This study investigates the impact of diagnostic instability of recurrence rates in depression and anxiety.
Methods: Data were derived from the Netherlands Study of Depression and Anxiety (NESDA). The sample of 656 participants had a panic disorder with or without agoraphobia, agoraphobia, social phobia, generalized anxiety disorder, major depressive disorder or dysthymia, and a subsequent remission. Recurrence rates of index disorders (diagnostically stable recurrence) and newly arisen anxiety or depressive disorders (diagnostically unstable recurrence), were calculated over a 4-year follow-up period.
Results: In anxiety disorders (n=281), the recurrence rate is more than doubled, from 23.8% with a stable recurrence, to 54.8%, when diagnostically unstable recurrences are included. In depressive disorders (N=173) the recurrence rate increases from 37.6% to 49.7%, and in comorbid anxiety and depressive disorders (N=202) the diagnostically unstable recurrences increase from 54.0% to 66.3%.
Limitations: Attrition during follow up may have biased the results; remission was defined as absence of symptoms for 1 month; very short-term remission and recurrence patterns were not assessed.
Conclusions: Diagnostically unstable recurrences have a significant impact on recurrence rates, with the greatest instability for anxiety disorders. When only diagnostically stable recurrences are assessed, recurrence rates are highly underrated and provide biased estimates of the true course of these disorders.
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