[Is the incidence of schizophrenia declining?: an investigation of the examination rates in the psychiatric clinics of a medical school hospital and a general hospital].
OBJECTIVE
Some researchers in Europe, America and Oceania have recently reported that the incidence of schizophrenia is declining. We investigated changes in the proportion of schizophrenic patients to the total number of patients in two Japanese hospitals during the last decade.


METHODS
The subjects were patients who first consulted the psychiatric clinic of Jichi Medical School or the psychiatric clinic of Kamitsuga General Hospital between December 1993 and November 1994 or between December 2003 and November 2004. Both clinics accepted new patients without prior appointments. Patients were classified using ICD-10 criteria (F0-F9, G40). The sex distribution of the patients and the mean age at first contact were compared for the two time periods. The proportion of schizophrenia (F2 in the ICD-10 criteria) to the total number of patients was compared for the two time periods after standardizing the populations with regard to age using the "1985 model population in Japan."


RESULTS
A decade ago, 398 patients first contacted the psychiatric clinic of the medical school hospital, compared with 958 patients in the recent investigation. A decade ago, 166 patients first contacted the psychiatric clinic of the general hospital, compared with 407 patients in the recent investigation. No differences in the sex ratios of the two groups were noted. The mean age of the patients visiting the medical school significantly increased by 3.5 years (36.9 to 40.4 years), while that of the patients visiting the general hospital significantly increased by 10.0 years (46.2 to 56.2 years). The proportion of schizophrenia patients in the medical hospital decreased from 8.5% to 6.9%, while that in the general hospital decreased from 11.0% to 5.4%. Only the change in the proportion of schizophrenia patients at the general hospital was significant.


CONCLUSIONS
The facts that the mean age of first-contact patients has risen and that the number of first-contact patients has increased approximately 2.5-fold suggests a change in the composition of first-contact patients in the last decade. We have some reservations regarding the comparison of these two groups. Although the actual number of first-contact patients with schizophrenia increased in both clinics, we found that the proportions of schizophrenia patients decreased in both clinics after standardizing the populations with regard to age. This finding must be investigated in view of other factors, including the overall age distribution of first-contact patients, increases in the proportions of affective disorders and organic mental disorders, and so on.
Toshitani
Kenji
K
Department of Psychiatry, Jichi Medical University. 2
Kobayashi
Toshiyuki
T
Osawa
Takuro
T
Kato
Satoshi
S
Eto
Shinkichi
S
Ojima
Toshiyuki
T
D017677:Age Distribution; D005260:Female; D006769:Hospitals, General / Q000706:statistics & numerical data; D006785:Hospitals, University / Q000706:statistics & numerical data; D006801:Humans; D015994:Incidence; D038801:International Classification of Diseases; D007564:Japan / Q000453:epidemiology; D008297:Male; D010044:Outpatient Clinics, Hospital / Q000706:statistics & numerical data; D011567:Psychiatric Department, Hospital / Q000706:statistics & numerical data; D012559:Schizophrenia / Q000175:diagnosis / Q000453:epidemiology*; D017678:Sex Distribution; D013997:Time Factors