Phenotypes in patients with monopolar and bipolar depression

Abstract

Introduction Recurrent depressive disorder is heterogeneous in respect to its etiology (predominantly exogenous or endogenous). Patients with recurrent depressive disorder (RDD) may change diagnosis to bipolar disorder (BD). Regarding the true RDD there is the possibility that in most cases it is exogenous, and the prevalence of endogenous RDD might be similar to BD. There is still debate regarding useful criteria for distinguishing between bipolar and monopolar depression especially at the first episode. Objectives The purpose of the study is to identify useful phenotypes that could help distinguishing between endogenous monopolar and bipolar depression. Methods The study was carried out on patients diagnosed with RDD and BD according to ICD 10 criteria. The following data was analyzed: socio-demographic parameters, family psychiatric history, seasonality, suicidal attempts, and behavioral phenotypes such as nicotine, alcohol, or illicit drug use. Results The study included 105 RDD and 74 BD patients. In the RDD sample the mean age at disorder onset was 45.93 years, while in the BD sample, was 32.45 years. Significant differences between the samples were found in: family psychiatric history (BD patients having more relatives with schizophrenia, P =0.01), smoking habits (BD patients smoking more cigarettes than RDD patients, P =0.001), and seasonal depression (mainly summer and winter in RDD, and mainly summer and autumn in BD). No differences were found regarding suicidal attempts, alcohol or illicit drug use. Conclusions Onset age, family psychiatric history, smoking habits, and seasonality may reflect endogenous depression (BD or RDD) or different subtypes of BD or RDD.