Incidence and distribution of first-episode mania by age: results from a 35-year study.
BACKGROUND
Few epidemiological studies have investigated incidence by age or age at onset distributions for mania or bipolar disorder. The current study aimed to determine these in a defined area in south-east London, over a 35-year period.


METHODS
All cases of first-episode mania presenting to psychiatric services in Camberwell, south-east London, between 1965 and 1999 were identified. Incidence rates by age, using 5-year age-at-onset bands, were estimated and the structure of the age-at-onset distribution for first-episode mania was investigated using finite mixture distributions (admixture analysis).


RESULTS
The incidence of DSM-IV bipolar I disorder (BP I), first manic episode peaked in early adult life (16.38/100,000 population per year in the 21-25 years band) with a much smaller peak in mid-life. A two-component normal mixture distribution fitted age at onset better than either a single normal distribution or a three-component mixture, implying the existence of early and later onset subgroups. The early onset group had a stronger family history of bipolar disorder, and showed more acute, severe and atypical symptoms during their first manic episode.


CONCLUSIONS
The incidence of mania peaks in early adult life but there is clear evidence of early and later onset subgroups which may represent different forms of disorder.
Section of General Psychiatry, Division of Psychological Medicine, Institute of Psychiatry, De Crespigny Park, London, UK. nkennedy@stpatsmail.com
N
N
Kennedy
B
B
Everitt
J
J
Boydell
J
J
Van Os
P B
PB
Jones
R M
RM
Murray
D000328:Adult; D017677:Age Distribution; D017668:Age of Onset; D001714:Bipolar Disorder / Q000175:diagnosis / Q000453:epidemiology*; D002391:Catchment Area, Health; D039721:Diagnostic and Statistical Manual of Mental Disorders; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D015994:Incidence; D038801:International Classification of Diseases; D008297:Male; D008875:Middle Aged; D015588:Observer Variation; D011159:Population Surveillance / Q000379:methods; D012008:Recurrence; D012720:Severity of Illness Index; D013997:Time Factors; D006113:United Kingdom / Q000453:epidemiology