Clinical correlates of age at onset distribution in bipolar disorder: a comparison between diagnostic subgroups

Abstract

Background: Admixture analysis of age at onset (AAO) has helped delineating the clinical profile of early onset (EO) bipolar disorder (BD). However, there is scarce evidence comparing the distributional properties of AAO as well as the clinical features of EO BD type 1 (BD1) with EO BD type 2 (BD2). To this end, we studied 515 BD patients (224 BD1, 279 BD2, and 12 BD not otherwise specified [NOS]) diagnosed according to DSM-IV-TR criteria.Methods: AAO was defined as the first reliably diagnosed hypo/manic or depressive episode according to diagnostic criteria. We used normal distribution mixture analysis to identify subgroups of patients according to AAO. Models were chosen according to the Schwarz's Bayesian information criteria (BIC). Clinical correlates of EO were analysed using univariate tests and multivariate logistic regression models. Results:A two normal components model best fitted the observed distribution of AAO in BD1 (BIC = −1599.3), BD2 (BIC = −2158.4), and in the whole sample (BIC = −3854.9). A higher number of EO BD2 patients had a depression-(hypo)mania-free interval (DMI) course, while a higher rate of (hypo)mania-depression-free interval (MDI) course was found in EO BD1. EO BD2 had also a higher rate of comorbidity with alcohol dependence compared to EO BD1. The latter finding was confirmed by multivariate logistic regression analysis. Conclusions:In conclusion, both BD1 and BD2 had bimodal AAO distributions, but EO subgroups had a diagnosticspecific clinical delineation.

Bipolar disorder: Trimodal age‐at‐onset distribution

“…Seven studies recruited patients from a clinic setting only, 9,15,23,27,29,34,35 two from community settings only 8,32 and two from inpatient hospital settings only 25,36 . Three studies recruited from both the clinic and the community, 24,30,31 three from both the clinic and hospital setting 5,28,33 and four studies recruited from the hospital, clinic and the community 7,14,22,26 …”

“…The largest of the included studies collected data on 4037 bipolar patients across 36 collection sites in 23 countries throughout Asia, Africa, Europe, North and South America and Australia 24 . Of the remaining studies, eleven were conducted in Europe, 5,7,8,22,23,25,28,29,31,34,35 six in North America, 9,14,15,32,33,36 one in Australia 27 and two articles combined data from collection sites in both North America and Europe 26,30 …”

“…There were three separate types of distributions found for bipolar disorder age at onset across the 21 articles. Fourteen studies showed a trimodal distribution, 5,7,8,15,25‐30,32‐35 five a bimodal distribution 9,14,22,23,36 and two studies examined cohort effects on AAO 24,31 …”