Bipolar Disorders: Mixed States, Rapid-Cycling, and Atypical Forms

264 P. Briegerare not the same’’ (Spitzer, 1998). Questions of methodology are important inunderstanding comorbidity (Brieger and Marneros, 2000). The growing importanceof spectra, of subthreshold, and of the subsyndromal disorders in psychiatry, as wellas the suspension of exclusionary principles, has led to an increase in comorbidity,which makes it complicated to appraise the potential consequences of twoco-occurring disorders.There is some indication that mixed states and rapid-cycling forms of bipolardisorders may have a worse prognosis than ‘‘typical’’ forms (Marneros and Brieger,2002), although when looking at empirical data, the difference may be neither asgreat nor as clear as is often assumed. One central question is whether mixed statesand rapid-cycling forms of bipolar affective disorders show patterns of comorbiditythat differ from those observed in other forms of bipolar affective disorders. Ifthat were true, it would make a case for viewing mixed states and rapid-cyclingforms of bipolar affective disorders as distinct groups. A basic problem here is thedifference between cross-sectional and longitudinal observations. Since the timesof Kahlbaum (1863) and Kraepelin 1909–1915), ( there has been a consensus that,in psychiatric research, longitudinal observation is superior to cross-sectionalobservation. Nevertheless, both the co-occurrence of two mental disorders andthe occurrence of mixed states and rapid-cycling forms of bipolar affective disordersmay be transient with potential low long-term stability. It is an overtweakness of present diagnostic systems, such as DSM-IV and ICD-10, that theypay little (or almost no) attention to such a long-term course. At the same time, itbecomes increasingly clear that complex interactions between long-term andsubsyndromal features of a disorder are important for its prognosis (Marnerosand Brieger, 2002).Medical conditions and neuropsychiatric disordersThe comorbidity of medical conditions and bipolar affective disorders is a topicthat warrants systematic research. The interaction between bipolar affective disordersand disorders of thyroid axis has received more attention than most othermedical conditions. Nevertheless, no clear picture has emerged. It has been discussedthat patients with mixed bipolar disorders may exhibit more thyroidhormone deficiency than controls (Zarate et al., 1997; Chang et al., 1998;McElroy et al., 2000), but there are also negative studies that have found nodifferences between bipolar affective patients with or without mixed episodes asregards thyroid hormones (Joffe et al., 1994), including a retrospective chartanalysis prepared in our department (Reinelt, 2003). A recent study of 443 bipolarpatients (Cassidy et al., 2002) showed no indication of ‘‘overt or subclinical thyroiddisease’’ in mixed manic episodes. In regard to rapid-cycling bipolar disorders,