Benjet C, Borges G, Medina-Mora ME, Méndez E, Fleiz C, Rojas E, Cruz C

Idioma: Español
Referencias bibliográficas: 30
Paginas: 155-163
Archivo PDF: 437.09 Kb.

RESUMEN

Introduction
The first and only nationally representative prevalence estimates of psychiatric disorders in Mexico (the Mexican National Comorbidity Survey) indicate sex differences in the expression of psychopathology and early ages of onset for most disorders, often in the adolescent years. Studies from other countries have shown that sex differences in the pattern of psychopathology vary by life stage, which in part, may be explained by different ages of onset for varying disorders. These studies also suggest that many of the sex differences in the prevalence of disorders emerge during the adolescent years.
However, scarce data is available on the epidemiology of adolescent psychopathology in Mexico, and much less regarding possible sex differences in the patterns of prevalence, severity and ages of onset. The purpose of this report, therefore, is to estimate sex differences in the 12-month prevalence and severity of 17 psychiatric disorders (using DSM-IV diagnostic criteria) as well as ages of onset in adolescents from Mexico City metropolitan area.
Materials and methods
This article provides data from the Mexican Adolescent Mental Health Survey. This survey has a multistage probability design and is representative of adolescents between 12 and 17 years old who reside in the Mexico City metropolitan area. The final sample included 3005 adolescents selected from a stratified multistage area probability sample. In all strata, the primary sampling units were census count areas cartographically defined and updated in 2000 by the Mexican National Institute of Statistics, Geography and Informatics (INEGI). Two hundred census count areas were selected with probability proportional to size. Secondary sampling units were city blocks, four of which were selected with probability proportional to size from each census count area. All households within these selected city blocks with adolescents aged 12 to 17 were selected. One eligible member from each of these households was randomly selected using the Kish method of random number charts. The response rate of eligible respondents was 71%.
The adolescents were interviewed in their homes by trained lay interviewers using the computerized adolescent version of the World Mental Health Composite International Diagnostic Interview (WHM-CIDI-A 3.0). The average length of the interview was two and a half hours. A verbal and written explanation of the study was given to both parents and adolescents. Interviews were administered only to those for whom signed informed consent from a parent and/or legal guardian were obtained as well as the adolescent agreement.
Because of the stratified multistage sampling design, data was subsequently weighted to adjust for differential probabilities of selection and non-response. Post-stratification to the total Mexico City Metropolitan Area adolescent population according to the year 2000 Census in target age and sex ranges were also performed. For prevalence estimates, due to this complex sample design and weighting, estimates of standard errors for proportions were obtained by the Taylor series linearization method using the SUDAAN software. Sex differences were evaluated using Wald χ2 tests. Statistical significance was based on two-tailed design tests evaluated at the .05 level of significance. Ages of onset for psychiatric disorders were estimated using discrete time survival analyses with person-years as the unit of analysis which in this article are presented as Kaplan-Meier curves.

Results
The most prevalent individual disorders in both sexes were specific phobia (15.6% for males, 26.1% for females) and social phobia (10.0% for males, 12.4% for females). For females, the most frequent disorders that follow in magnitude after these two types of phobias are, in decreasing order, major depression (7.6%), oppositional defiant disorder (6.9%), agoraphobia without panic (4.7%) and separation anxiety disorder (3.6%). On the other hand, for males, the most frequent disorders after specific and social phobia are oppositional defiant disorder (3.7%), alcohol abuse (3.4%) and conduct disorder (3.3%). Overall, females reported a larger number of disorders and a greater prevalence of any disorder.
With regards to disorder severity, mood disorders have the greatest proportion of severe cases and anxiety disorders the smallest proportion of severe cases. While this pattern is found for both males and females, there are sex differences in severity such that females have a greater proportion of severe cases overall (25.5% were severe cases compared to 18.9% for males).
The earliest ages of onset were found in anxiety disorders, followed by impulse control disorders, and mood disorders with substance use disorders having the latest ages of onset. The ages of onset for anxiety, mood and substance use disorders are similar between males and females. However, males developed at earlier ages the onset of impulse control disorders than females, and this is due primarily to oppositional defiant disorder rather than to attention deficit hyperactivity disorder or to conduct disorder.
Discussion
The greater overall prevalence and severity of psychiatric disorders in adolescent females in comparison to adolescent males suggests that adolescence may be a period of greater vulnerability for females. Our findings with regards to a higher prevalence of mood and anxiety disorders in adolescent females in comparison to males are consistent with those reported in the international literature. However, our findings of more impulse control disorders in females than males are inconsistent with most international reports excepting a study of Finnish adolescents in which adolescent girls reported more internalizing and externalizing disorders than their male counterparts. The greater prevalence of impulse control disorders in our study is due to oppositional defiant disorder, not attention deficit hyperactivity or conduct disorder. The lack of sex differences in substance use disorders is consistent with recent findings in Mexican adolescents which show a narrowing of the sex gap difference in substance use. There are both biological and psychosocial theories which may explain the greater vulnerability in adolescent girls such as gender role intensification and socialization during adolescence; a higher exposure to adversity, stress and negative life events; as well as a greater reactivity of the hypothalamic-pituitary-adrenal axis when confronted with stress.
Study limitations include the willingness of participants to disclosure sensitive or potentially embarrassing information as well as potential sex differences in willingness. While females reported more disorders and greater severity of disorders overall, sex differences in response style are not likely, since females reported more of many, but not all disorders. A further limitation is the use of trained lay interviewers instead of clinicians. The development and use of fully structured diagnostic instruments such as the CIDI have greatly helped to tackle this limitation in general population surveys and data suggest that diagnoses provided by these fully structured instruments approximate adequately clinical diagnoses.
Keeping in mind these limitations, the results of this study are relevant for clinical practice as well as for the epidemiological surveillance of our population to guide service planning and public health policy.

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