Longitudinal syndromal and sub-syndromal symptoms after severe depression: 10-year follow-up study

BACKGROUND: Few follow-up studies of depression have evaluated depressive symptomatology over time at both threshold and sub-threshold levels. AIMS: To evaluate long-term longitudinal symptomatic course after an episode of severe depression. METHOD: A total of 61 participants from a previous study cohort underwent a detailed interview covering the longitudinal course of depression and pharmacological treatment over 8-11 years of follow-up. RESULTS: Of the follow-up months, 52% were spent at an asymptomatic level, 15% at minor symptom level, 20% at residual symptom level and 13% at full depression level. Also, 30% of follow-up months were spent in an episode of depression, and 18% of patients never achieved asymptomatic status during follow-up. The percentage of patients at each symptom level remained relatively stable after the first 2 years, but levels in individuals fluctuated, with a mean of two changes in symptom levels per follow-up year. CONCLUSIONS: After severe episodes, sub-syndromal levels of depression are common and persistent, with considerable fluctuation suggesting a continuum between sub-syndromal subtypes and full depression.