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

253 Atypical features of bipolarity in old ageAge of onset and clinical courseAge of onset can be an important variable that distinguishes subtypes of mania andbipolar disorder in order to improve understanding of underlying pathogenesis(Young and Klerman, 1992). While the vast majority of bipolar disorders in ageneral population occur early in life (Goodwin and Jamison, 1984), elderlybipolar patients report a mean age of onset of mood disorder which ranges fromage 40 to 47 years and an onset of mania that ranges from age 51 to 60 years (Chenet al., 1998). This latter group used a cut-off for ‘‘late onset’’ at 60 years but Wylieet al. (1999) have suggested that median age at onset in mixed-age patients couldreasonably be used as a cut-off point between early and late onset. Clearly, themean age of onset is also influenced by the cut-off for the age considered ‘‘elderly’’.In the Wylie et al.(1999) sample, their ‘‘elderly’’ bipolar patients were over the ageof 60 and had a median age of onset of approximately 50 years. While no clear-cutconvention for ‘‘late onset’’ has been established in an elderly population, the workby Wylie et al.(1999) suggests that an age of approximately 50 years would seem areasonable marker for future use. Using this cut-off for a late-onset group ofelderly bipolar patients, they found an increased prevalence of psychotic featuresand an increase in cerebrovascular risk factors.In another study of elderly bipolar subjects with a mean age of 74 years, anincrease in vascular comorbidity was found in a late-onset group defined by a cutoffpoint of age 50 years (Hays et al., 1998). In this study, despite the elderly cohortand late-onset subjects, the proportion of patients with a positive family historywas extremely high (83%), even for the late-onset group. Generally, within anelderly bipolar population, there has been a trend towards a higher rate of positivefamily history in those with an earlier age of onset (Hays et al., 1998; Stone, 1989).For elderly individuals with comorbid neurological disorders there is a tendency tohave a lower rate of family history (Tohen et al., 1994). However even in theneurological subgroup of patients, a significant positive family history in firstdegreerelatives still applies at approximately 30%.In a Finnish study, the annual rate of hospitalization by age for all bipolar patientshas been recorded by Rasanan et al. (1998). Although the peak 1-year incidenceoccurred in middle age for both sexes, almost 20% of all first admissions for mania stilloccurred after the age of 60. This is consistent with the bimodal distribution found in anumber of bipolar studies (Angst, 1978; Petterson, 1977; Sibisi, 1990). Two studies(Spicer et al., 1973; Sibisi, 1990) found the highest inception rates for males to be inlate life and for females the inception rates tended to be highest in middle age or later.Whether age of onset is determined by episode or hospitalization can make asignificant difference. Community surveys such as the Epidemiologic CatchmentArea (ECA) study (Weissman et al., 1991) and the National Comorbidity Study(Kessler et al., 1997) report the mean age of onset of bipolar disorders as 21 years.