Is Autism Rising?
Autism as a diagnosis is constantly changing
Posted Aug 12, 2011
Autism is everywhere. Autism is in the media and autism is in my neighborhood. According to the media, autism is caused by vaccines and anti-depressants (Croen, et al., 2011). Both fraternal and identical twins have it http://www.nytimes.com/2011/08/09/health/views/09klass.html. Autism is also in my neighborhood and among my friends. The boy next door is autistic and the boy at the community swimming pool is autistic. Two friends have autistic sons. Yesterday, a teacher told me one of the kids in her class was autistic. Autism appears to be everywhere. How is this possible when just a generation ago it was extremely rare? Is autism on the rise? Is there an epidemic of autism? And, why do the media automatically jump to environmental hazards as the explanation? It is more or less assumed these days that autism has increased and it is due to environmental pollutants, medical pollutants, or fetal pollutants. Let's take a closer look at this important topic.
This is not a simple question and there is no simple answer. Yes, autism is being diagnosed more frequently than in the past. An epidemiological study conducted in 1966, reported the rate of autism as 4 or 5 cases in 10,000 (Croen, et al., 2011). The DSM-IV TR (APA, 2000) reports the range of rates from 2 to 20 cases per 10,000 with a median of 5 cases per 10,000. More recent data reported by the CDC monitoring network (2009) sets the rate of 100 cases per 10,000 or 1% http://www.cdc.gov/mmwr/preview/mmwrhtml/ss5810a1.htm. This is obviously much higher than previous reports. What happened? What explains the increase in the prevalence of autism? This increased rate in diagnosis of autism has concerned the mental health community for a decade or two. But, does this increased diagnosis indicate an increase in true cases of autism or can it be explained by other variables?
One explanation of the increased rates is definitional. In the past, the term "autism' was limited to autistic disorder and believed to be very rare. Symptoms of autistic disorder included severe impairment in social interaction, delayed or total lack of spoken languages and stereotyped behaviors such as head banging. These children were rarely seen in the neighborhood and more likely to be institutionalized. It was a serious disorder, similar to childhood schizophrenia and diagnoses were strictly defined. In more recent years, autism has been much more broadly defined. Referred to as Autistic Spectrum Disorder or ASD, it includes Aspergers and many high functioning children.
Autism as a diagnosis is constantly changing. While a specific cluster of symptoms was observed and labeled "autistic" by Leo Kanner as early as 1943, psychiatrists were more likely to label these children emotionally disturbed. Thirty years ago, when I was an intern in psychiatry, autism was extremely rare. Children who today may be diagnosed as autistic or Aspergers were either not diagnosed, labeled mentally retarded or classified as childhood schizophrenia. Autism, by definition, was extremely rare and required language impairment, stereotyped behaviors, and early onset. Over time, as the Diagnostic and Statistical Manual (DSM) evolved so did autism.
For example, compared to earlier versions of the DSM, the DSM-IV-TR (2000) has separate diagnostic categories for autistic disorder, Rett's Disorder, Asperger's Disorder, and pervasive developmental disorders - NOS. When the DSM-IV came out, psychiatrists believed that Aspergers was sufficiently different from autism to be included as a separate diagnostic category. At the time, it was seen as a separate condition from autism without language delay, without delay in cognitive development, and with more variable motor delays. Even though it was unclear whether Aspergers was a form of high functioning autism or a separate condition, DSM-IV authors listed it as a separate condition to encourage further research (APA, 1997).
In contrast, the DSM-5 workgroup is proposing deleting Aspergers as a diagnostic category. Their rationale is that Aspergers can be subsumed by Autistic Spectrum Disorder (AS), that Aspergers is high-functioning autism, and language impairment is no longer a criterion for an autistic diagnosis. The aim of DSM-5 draft criteria is that anyone with a significant impairment in social-communication and repetitive/restricted behavior will meet autistic spectrum disorder (ASD) criteria. This wider category will certainly increase diagnosed cases of autism. If Asperger's no longer exists, how has autism changed?
As I mentioned earlier, a generation ago, autism was very narrowly defined and rare. As of 2000, the DSM-IV-TR specified that the disturbance must be manifest by delays or abnormal functioning prior to age 3 years. In contrast, the proposed DSM-5 calls autism a spectrum disorder that is neurodevelopmental and present from infancy or early childhood. The subtle changes in wording are critical and represent paradigm shifts in thinking. Where autism was once described behaviorally by Kanner or treated as a developmental delay by educators, it is now conceptualized as a neurological disorder. Clearly, there has been a shift from a behavioral-educational model to a neuropsychological model.
So, the question remains: is autism rising? Yes, diagnosed cases of autism are increasing and are likely to continue with broader diagnostic categories. But, do these diagnostic trends reflect a true increase in the prevalence of autism? And if these increases are true, what is causing them? This remains unclear. There are many possible explanations for increases in autism - some true and some artifactural. Explanations include: broader diagnoses, earlier detection, increased awareness, increased funding, varied data collection techniques, vocal parents, genetics, prenatal and infant exposure to toxins, increased scientific knowledge, and trends in mental health.
Autism is not due to one, single cause. This is a gross oversimplification of a complex problem. Autism has multiple causes and no one completely understands it. But, one thing is agreed on. Autism is increasing in diagnosed cases, which makes it an important public health concern. And, there is considerable exciting research on its etiology, for example the CHARGE study at UC Davis, which I will discuss in future posts. Keep reading...
American Psychiatric Association. (1997). DSM-IV Sourcebook, Volume 3. Washington, DC Author.
American Psychiatric Association. (2000). Diagnostic and statistical manual of mental disorders. (4th ed., text revision). Washington, DC: Author.
Croen, L.A., Grether, J.K., Yoshida, C.K., Odouli, R., Hendrick, V. (2011). Antidepressant Use During Pregnancy and Childhood Autism Spectrum Disorders, Arch. Gen Psychiatry. Published online July 4, 2011.