Mood disorders: pearls of wisdom from a lifetime of observation

83 years of age, Professor Angst still takes more than a keen interest in research into mood disorders and in particular is actively engaged in analysing the data collected from an epidemiological cohort he began to observe more than 30 years ago.1 Furthermore, he still does not shy away from questioning perceived wisdom when data he and his colleagues have collected point to a different conclusion. Prospective trials show that there is a high lifetime prevalence of psychiatric disorders – of the order of 40-50 per cent1-5 – and prevalence rates for mood disorders, anxiety disorders and substance abuse/dependence of 20-30 per cent. Professor Angst personally felt that in reality the prevalence rates for psychiatric disorders may be higher because the figures are based on retrospective data and not lifelong prospective studies. However, the lifetime prevalence rates of major depressive disorder (MDD) compared with bipolar disorder (BD) have been generally overestimated in Professor Angst’s view. The discrepancy may be due to trial selection criteria largely based on the classification systems, DSM-IV and ICD-10. So, instead of the 1:1 ratio of MDD to BP Professor Angst and colleagues have observed in the Zurich study,1 others have recorded much higher ratios of MDD to BP of around 4:1.2-5 If broader diagnostic criteria that reflect more closely the real-life experience of those with mood disorders are applied to patient populations, then a higher proportion of bipolar disorders would emerge. For example, when Professor Angst’s diagnostic specifier for bipolarity6 criteria were applied to studies where the ratio of MDD to BP is much higher than 1:1, then overdiagnosis of major depressive disorder was reduced, revealing a higher proportion of patients with bipolar disorders; this was the case in a patient study across 18 countries7 and in two well-known prospective epidemiological studies (EDSP Munich,8 NCS-R USA9). Identifying such ‘hidden’ or subthreshold bipolar patients might make it possible to make an earlier diagnosis of bipolar disorder, for which there is an average delay of 10 years from onset of depressive symptoms, and perhaps specific treatment could be employed earlier. In any case, Professor Angst explained, the risk of someone with depression becoming bipolar is about 1.25 per cent per year – and the risk of becoming bipolar remains the same no matter how many episodes of depression have been experienced before a hypomanic or manic episode manifests. So that, he argued, if people with depression lived to be more than a 100 years old, they would all become bipolar. The risk of switching from mania to depression is 3 per cent per year.