Toward validation of atypical depression in the community: results of the Zurich cohort study.

AIMS: This paper (1) examines the validity of the atypical subtype of depression in a community-based longitudinal cohort study, (2) presents estimates of the prevalence and sex differences of DSM-IV atypical depression and a newly more broadly defined atypical syndrome in the community and (3) compares the clinical correlates and treatment patterns of those with atypical depression with other depressives.
METHODS: The Zurich cohort study is comprised of 591 subjects selected from a population-based cohort of young adults representative of the canton of Zurich in Switzerland, who were screened in 1978 with the Symptom Checklist 90-R [L.R. Derogatis (1977)] and followed prospectively with five interviews between 1979 and 1993. Atypical depression was defined on a spectrum ranging from atypical major to minor to atypical depressive symptoms alone.
RESULTS: The rate of DSM-IV atypical major depressive episodes in this community is 4.8% and for major atypical depression syndrome is 7.3%. Whereas there was no marked sex difference for nonatypical features, there was a significant female preponderance for DSM-IV and broadly defined atypical depressive subtypes. Systematic investigation of the diagnostic criteria for atypical depression revealed that a nonhierarchical definition of atypical depression with respect to mood reactivity yielded as valid a syndromic definition as the current hierarchy based on mood reactivity as an essential feature. Very high comorbidity (odd ratios>2.0) was found with seasonality, bipolar II, social phobia, binge eating, neurasthenia and sociopathy. LIMITATIONS: Atypical depression was not defined à priori, its criteria were derived from two sections of the Zurich interview.
CONCLUSIONS: Atypical depression has high population prevalence and substantial significance in terms of clinical severity, impairment, and service use. The intriguing finding that the sex difference in depression may be attributed to atypical features of depression will need further investigation. Overall, our data indicate that the atypical subtype of depression is a valid entity based on evidence from such traditional indicators of validity as inclusion criteria and indicators of course. However, there are some problems with discriminatory validity from other disorders. Although comorbidity with these disorders may in part reflect an operational artifact of symptom overlap, further work needs to be done in distinguishing atypical depression from bipolar II.