Terminology for Follow-up
Aggregation of findings across studies in this review was complicated by the use of different terminology for characterizing both the index and follow-up information.54 The important distinction between syndromic and symptomatic recovery26 has been valuable in separating response to treatment while still characterizing residual symptoms, particularly of other target disorders. This highlights the need for the collection of a deeper characterization of phenotypes through both comprehensive diagnostic interviews and dimensional ratings. Recent efforts, such as the proposal for a common global nomenclature to define the course and outcome in BDs by a task force under the auspices of the International Society for Bipolar Disorders,55 should facilitate the comparability of outcome studies across countries.
Source of Samples
The growing gap between clinical samples that form the basis for first-onset studies and community samples is an important source of bias in the depiction of the course of BD in the population. International community studies have also shown that fewer than half of those with BD receive treatment by a mental health specialist.2,25 As expected, treatment in the mental health specialty sector is far more common among those with high levels of comorbid mental and physical disorders, suicide attempts, and severe impairment.56 This gap already emerges in adolescence, as shown by Khazanov and colleagues,57 who found that only about half of a nationally representative sample of adolescents with BD had received treatment for depression or mania. Those youth with BD who had received treatment were more likely to have multiple comorbid conditions, particularly substance use or behavior disorders, functional impairment, and disability, than were those who had not been treated. These findings suggest that caution should be exerted when generalizing from such samples to BD in general, particularly regarding patterns of comorbidity, impairment, and disability that may lead to referral to specialty settings, as well as the recognition of BD among youth. Therefore, the course of BD in samples identified in clinical settings may not be generalizable to the outcome of BD in the general population. The generally poor outcome of the prospective studies of the course of BD reviewed in this chapter may only reflect that of severe BD that leads to specialty or inpatient treatment. Integration of clinical and community-identified samples of BD would provide a more comprehensive portrait of BD in the population and its public health significance.
Even within clinical samples composed of patients with severe symptoms or disability associated with BD, there is great variability in the demographic and clinical characteristics of the samples. Many of the studies of illness and functional course are limited to inpatient samples12-14,17,29 or specialty treatment settings for BD,9 whereas others attempted to sample more broadly from both inpatient and outpatient settings8-10,19 thus potentially reflecting different levels of severity, prior treatment, and antecedent nonaffective disorders. Therefore, characterization of the demographic and clinical characteristics of patients in such studies is critical to an evaluation of comparability of results across settings.