CONTEXT Autism is a neurological disorder characterized by early impairments in the overall development of cognitive, speech and relational functions. It is one of a family of pervasive developmental disorders (PDDs). The clinical picture of autistic disorder is highly variable, and its management requires multiple resources and various intervention methods. Language therapies and socialization and behavioural interventions can change the course of autistic disorder but cannot cure it. Since none of these numerous therapeutic approaches stands out as being the most effective, the modalities for optimal management have not yet been determined, and research continues. This situation has prompted researchers to try new management and therapeutic approaches, including hyperbaric oxygen (HBO) therapy. Experiments with this modality are based on the physiological effects that pressurized oxygen can have on the brain. However, autism is not on the list of indications officially recognized by the Undersea and Hyperbaric Medical Society (UHMS), an international learned society with more than 2,500 members in about 50 countries. The question of the role of hyperbaric oxygen therapy in managing autistic disorder is, therefore, still unresolved. This is why the Minister of Health and Social Services asked AETMIS to examine this matter in the broader context of an update of the report published in 2000 by the Conseil d'évaluation des technologies de la santé (CETS), AETMIS's predecessor, on the conditions for the treatment of which the efficacy of HBO is supported by evidence. In his request, the Minister also singled out cerebral palsy, on which AETMIS has already published a report, dated January 2007. The present assessment, which is based on an exhaustive literature review, focuses on the efficacy of HBO in managing autistic disorder. HYPERBARIC OXYGEN THERAPY The UHMS defines hyperbaric oxygen therapy as the inhalation of pure oxygen (100%) by an individual placed in a chamber at a pressure greater than one atmosphere absolute (ATA). There are other definitions in the literature, but they are not the product of a consensus. The basis of this treatment modality is that oxygen compressed to pressures up to 2 or 3 ATA reduces symptoms, helps cure or simply does cure certain illnesses, such as refractory wounds. There are two types of hyperbaric chambers multiplace and monoplace. The choice of type of chamber depends on the need and the disease to be treated. HBO is recognized as a generally safe modality, and it has few contraindications. It does, however, carry certain risks, which should be taken into consideration when using it, namely, the risks involved in handling oxygen, such as fire and explosion, and those associated with pressure, such as traumatic injury to the middle ear, sinuses, lungs and teeth. RESULTS OF THE LITERATURE REVIEW Information on hyperbaric oxygen therapy and autism can be divided into two main categories a large body of gray literature, including anecdotal cases, which is available on different websites, and a very small body of scientific literature. The paucity of published studies prompted us to expand the inclusion criteria to ensure that the greatest possible number of information sources would be identified. Two descriptions of isolated cases were published in non-peer-reviewed journals or in conference abstracts, the first description dating back to 1994. HBO reportedly had positive effects, but the validity of this result cannot be established. The three case series studies identified involved small numbers of

subjects:

6, 14 and 18 children. In the first one, the three standardized evaluation instruments used seem to have shown a reduction in symptoms, but the authors acknowledge that their study has substantial limitations and conclude that this research needs to continue. The second study, which is briefly described in a conference abstract, shows, according to the author, improvements in a number of areas (measured by a single instrument), but their validity cannot be demonstrated. The third case series study, which was also presented at a conference, reports improvements in different areas measured with five standardized instruments, but the authors point out that these results observed in 15 children must be validated by further and better-structured studies. The only randomized, controlled trial that has been carried out was published only as a doctoral thesis. Furthermore, its contribution to the evidence is very small. This is because its primary objective was to develop a measuring instrument for assessing the effect of HBO on autism symptoms. The study did not compare HBO with another treatment modality but instead compared two pressure protocols 1.75 ATA versus 1.3 ATA (control group). Lastly, the sample consisted of only 10 patients. The higher pressure reportedly yielded better results in terms of symptom reduction, but the author herself mentions the substantial limitations of her study. In addition, we identified five ongoing or recently completed studies in the United States, but their results have not yet been published. There are significant differences between these studies' designs.

CONCLUSION:

Upon the completion of this systematic literature review, we observe that this is a topic of recent interest. The scientific data available at this time are of low quality, and the level of evidence does not enable one to build a strong case for the efficacy of this treatment modality in managing autistic disorder. The five ongoing studies identified are examining this matter from different perspectives. However, the differences in the HBO protocols and the small patient samples raise questions and foreshadow mixed results, which could compromise these studies' validity. In these circumstances, a literature watch should be conducted to evaluate the results of these studies as soon as they are published. In short, for the management of autism, hyperbaric oxygen therapy should, for now, be considered an experimental treatment modality. Consequently, in Québec, it should be limited to formal research projects.