With the recent publication of the fifth edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-5) there have been changes to the classification of Asperger’s Syndrome. Instead of being considered as a separate diagnosis, Asperger’s Syndrome is now classified within the umbrella term of Autism Spectrum Disorders. These changes have sparked much debate within the community and have potentially important implications for individuals with Asperger’s Syndrome and their families. In a new study published in BMC Medicine, Frank Duffy and colleagues from Boston Children’s Hospital and Harvard Medical School, USA have used electroencephalogram (EEG) spectral coherence to try to differentiate individuals with Asperger’s Syndrome from those with Autism Spectrum Disorders. Duffy told us more about the importance of this research and its implications for individuals with Asperger’s Syndrome.
What led to your interest in electroencephalography and its applications in Asperger’s Syndrome (ASP) and Autism Spectrum Disorders (ASD) research?
My forty years of experience reading clinical electroencephalograms (EEG) led me to believe that there is more information contained within EEG than is typically recognized and that EEG likely detects a broad expanse of brain differences that go well beyond EEG’s traditional application to the study of epilepsy. My experience in the clinical evaluation of ASD and ASP patients led me to believe that there must exist quantifiable differences in electrical activity patterns embedded in the EEG recordings of these distinct patient groups. So I used my electrical engineering background to facilitate the development and extraction of objective, quantitative, physiological measurements derived from EEG in diagnosing and better understanding these disorders.
How has the classification of Asperger’s Syndrome changed with the new DSM-5 diagnostic criteria?
DSM-5 eliminates Asperger’s Syndrome as a separate diagnosis from Autism Spectrum Disorders and folds it instead into Autism Spectrum Disorders or offers as an alternative diagnosis Social Communication Disorder.
Why is it so important to establish whether Asperger’s Syndrome is a diagnosis separate from Autism Spectrum Disorders?
There are three main reasons. Firstly, children with Asperger’s Syndrome and those with ASD differ in terms of their academic and their behavioral functioning and therefore in terms of appropriate academic placement and remediation. Placing them in the same broad category leads to inappropriate services and the lack of funding or reimbursement for the more specialized services indicated for each.
Secondly, much research into the underlying physiology of these patient groups involves tests that require subject cooperation and compliance with instructions. This is especially true for neuroimaging studies such as MRI and functional MRI where the inability to stay still may obviate a study altogether. This is more likely to be of issue in patients with ASD rather than ASP, leading to a bias of subject selection towards ASP. However, when patients with ASP are folded into the broader ASD population, results of the imaging studies that were successful may be attributed erroneously to the entire ASD population, although they may reflect findings that are specific for just the higher functioning ASP group. Fortunately, in contrast to MRI, EEG can be performed successfully on even the most ‘difficult’ ASD subjects.
Lastly, there is the loss of the ‘Asperger’ identity and name itself. I was approached by a senior official of the well-established and highly effective Asperger’s Association of New England who asked me, only partly in jest, “What will we call ourselves now? We essentially no longer exist.” A great many of their clients owe their schooling, employment and, to a large degree, their successful functioning in daily life to the specialized work done by this and similar organizations. Their recognition and support should be augmented, not diminished.
What is EEG spectral coherence and how does it help in trying to identify whether there is a difference between Asperger’s Syndrome and Autism Spectrum Disorders?
EEG spectral coherence measures the degree to which EEG signals from two electrodes on different regions of the scalp are ‘coupled’ (i.e. similar over time) and is a reflection of the extent to which the brain regions beneath the two electrodes are functionally connected and communicate with each other (i.e. work together). High coherence between brain regions is taken as an indication of high functional connectivity of those brain regions and low coherence as low functional connectivity. Certain clinical populations may have certain signature EEG coherence patterns, that is to say, they may show unique patterns of brain connectivity. Thus, measuring EEG coherence in patients with ASP and ASD and finding unique differences in their coherence patterns helps to identify brain functioning differences between these populations. This may be helpful not only in the diagnosis of these disorders but in the classification of as yet undetected, additional sub-populations of ASD.
What further research is needed to determine whether Asperger’s Syndrome is distinct from the higher-functioning end of the autistic spectrum?
A much larger ASP population will be required to conclusively determine, by EEG coherence, whether ASP constitutes the high functioning tail of the ASD population or whether ASP constitutes a physiologically unique entity. The dilemma lies in the fact that we seek funding for the evaluation of an entity that officially, i.e. by DSM-5 criteria, ‘no longer exists’!
Are there any implications for using EEG in the diagnosis and management of ASD or Asperger’s Syndrome?
There are at least two important implications. Firstly, it is generally agreed that the categorization of disorders in the Diagnostic Statistical Manual (DSM) is a process that remains ongoing as science continues to shed new light on currently established classifications. At present the criteria used in the DSM-5 classification of Asperger’s syndrome and ASD are based mostly on the observable behavior of patients. Many have bemoaned the lack of objective measures to assist in this classification process. Hopefully, objective, quantitative measures from EEG as well as neuroimaging, genetics and other objective techniques may serve to assist in further refining the classification criteria for ASD and its subgroups. Some advantages of achieving this using EEG over other imaging methods arise from its low-cost, safe, non-invasive, readily available, easily quantifiable, and potentially portable nature. Moreover, it can be easily and repeatedly administered thereby facilitating before and after studies to evaluate effects of new therapies.
Secondly, I do not recommend, at this time, that EEG should replace a thorough clinical evaluation of patients with ASD or ASP performed by appropriately trained physicians and/or psychologists. I do suggest a role for EEG in research for a more definitive differentiation of ASD and ASP as well as ASD subgroup classification. I also recommend its use as an objective tool for the measurement of therapeutic treatment effectiveness. EEG may also serve as a highly promising, low-cost preliminary screening tool for medically underserved populations of developing nations.
Questions and introduction from Stephanie Harriman, Deputy Medical Editor for BioMed Central.