Review

Continuing Medical EducationNature Clinical Practice Neurology (2008) 4, 138-147
doi:10.1038/ncpneuro0731  
Received 29 June 2007 | Accepted 15 November 2007 | Published online: 5 February 2008

Diagnosis of autism spectrum disorders in the first 3 years of life

Rebecca J Landa  About the author

Correspondence Kennedy Krieger Institute, 3901 Greenspring Avenue, Baltimore, MD 21211, USA

Email landa@kennedykrieger.org

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Learning objectives

Upon completion of this activity, participants should be able to:

  1. Describe the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV) criteria for the diagnosis of autism spectrum disorders (ASD).
  2. Identify the proportion of parents who recognize patterns of developmental disruption in children who subsequently develop ASD.
  3. Recognize types of impairment in infants that may predict a later diagnosis of ASD.
  4. Describe the recommendations of the American Academy of Pediatrics for autism-specific screening in children.
  5. List the recommendations for early intervention that are likely to improve the prognosis of ASD.

Competing interests

The author declared no competing interests. Désirée Lie, the CME questions author, declared no relevant financial relationships.

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Summary

Autism spectrum disorders (ASDs) are a class of neurodevelopmental disorders defined by qualitative impairments in social functioning and communication, often accompanied by repetitive and stereotyped patterns of behavior and interests. The term 'ASD' encompasses autism, pervasive developmental disorder not otherwise specified, and Asperger's syndrome. ASDs show etiologic heterogeneity, and there is no definitive medical test or cure for these conditions. Around 1 in 150 children have an ASD, with males being affected three to four times more frequently than females. The age at diagnosis of ASD ranges from 3 to 6 years, but there is increasing evidence that diagnosis in the second year of life is possible in some children. Early diagnosis will lead to earlier behavior-based intervention, which is associated with improvements in core areas, such as social functioning and communication. Early detection of—and intervention to treat—ASD is crucial because it is likely to lead to an improved outcome.

Review criteria

PubMed was searched for articles on early symptoms of autism and intervention studies published from January 1993 to August 2007. Search terms included "autism" and "autism spectrum disorders", in combination with "early detection", "early diagnosis", "early intervention", or "regression". Abstracts and relevant articles were reviewed and checked for new information. One intervention study published before 1993 was included in this Review. One review article published after August 2007 was also included.

Keywords:

autism, autism spectrum disorder, early detection, early diagnosis, early intervention

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Introduction

The term 'autism spectrum disorder' (ASD) refers to a class of neurodevelopmental disorders characterized by qualitative impairments in the development of social and communication skills, often accompanied by stereotyped and restricted patterns of interests and behavior, with onset of impairment before 3 years of age (definition based on the criteria for pervasive developmental disorders in the Diagnostic and Statistical Manual of Mental Disorders, fourth edition [DSM-IV®; American Psychiatric Association, Washington, DC]).1 ASDs include the diagnostic categories of autism, pervasive developmental disorder not otherwise specified (PDD-NOS), and Asperger's syndrome, and they occur in about 1 in 150 children.2

The DSM-IV® diagnostic criteria for ASDs were established in children aged 3 years and older, and it is not yet clear whether they are appropriate for younger children. Nevertheless, an increasing emphasis is being placed on earlier detection of ASDs. There are two main reasons for this change: first, there is mounting evidence that developmental disruption is present before 3 years of age in children who are subsequently diagnosed with ASDs; and second, evidence from research on neuroplasticity3 and intervention for ASDs indicates that early intervention is likely to optimize the outcome for children with ASDs.4, 5, 6

In this article, I review the evidence for early developmental disruption in children with ASDs and discuss the stability of early diagnosis of an ASD, early ASD-specific screening, and early intervention. Table 1 summarizes the signs of developmental disruption identified in retrospective video analysis studies and prospective studies of ASDs in the first 2 years of life. I shall focus only on autism and PDD-NOS, which are usually diagnosed between 3 and 6 years of age.7 These conditions will be referred to collectively as ASDs, unless the cited literature specifies one condition or the other.

Table 1 Social, communication, and other developmental disruptions reported before 24 months of age in retrospective and prospective studies of children later diagnosed with an autism spectrum disorder.
Table 1 - Social, communication, and other developmental disruptions reported before 24 months of age in retrospective and prospective studies of children later diagnosed with an autism spectrum disorder.
Full tableFigures & Tables indexDownload PowerPoint slide (162K)

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Developmental disruption in the first 2 years of life

Parental concerns

Parental concerns that a child has an ASD can arise as early as the first year of life, but they are most likely to arise when a child who is later diagnosed with an ASD is at a mean age of 18 months.8 Approximately 80% of parents of children with ASDs notice abnormalities in their child by 24 months of age, which usually involve delays in speech and language development9 and, less often, social, play, sensory, motor,10 or medical problems, or regulatory problems related to sleep, eating and attention.9 One study reported that, in cases in which parents became concerned in the child's first year of life, the diagnosis at 4 years of age was more likely to be autism than PDD-NOS.11 There is an average delay of 13 months between the mean age at first evaluation and the initial diagnosis of ASD.12 The age at first evaluation is related to the level of impairment, such that individuals with more-severe impairments tend to be diagnosed at a younger age.12

Retrospective studies involving home videos

Observation of early signs of ASDs by researchers was first made possible through analysis of home videos of infants and toddlers later diagnosed with ASDs.13 Before 9 months of age, children with ASDs might show signs of developmental disruption in social behavior (e.g. gaze avoidance or looking at people infrequently, absence of emotional expression, and poor social initiative) and in motility (e.g. hypoactivity).14, 15 One group estimated that 87.5% of children with ASDs displayed such symptoms before their first birthday.15 Some studies that used this retrospective approach also included a comparison group of children with typical development, and two studies included a group of children with non-ASD-related developmental delays.16, 17 Children with a later diagnosis of ASD could be differentiated from those with typical development or mental retardation at around the time of their first birthday by less frequently responding to their name16 and less frequently looking at the faces of other individuals.17 In addition, 12-month-old children who were later diagnosed with ASDs differed from those with typical development by less often using a pointing gesture to request or to share interest.17, 18, 19 A limited variety of gestures in children aged between 9 and 12 months was reported to be associated with a subsequent diagnosis of ASD in one retrospective study.20

Prospective studies involving infant siblings of children with autism spectrum disorders

The earliest behavioral indicators of ASDs are being revealed in well-controlled prospective, longitudinal studies involving infant siblings of children with autism (hereafter referred to as 'SIBS-A'), who are at increased genetic risk of an ASD.21, 22, 23

This is a relatively new approach to the study of ASDs, and so far only two studies have reported on a sizeable number of 6-month-old SIBS-A who were given diagnostic classifications at 2–3 years of age24, 25 — the time at which the diagnosis of ASD becomes more stable (see below). The evidence so far indicates that 6-month-old children who later become diagnosed with an ASD are likely to score within normal limits on standardized tests of visual perception and language development,25 but around a third of these infants score in the impaired range on standardized motor scales.24 Motor abnormalities include one or more of the following: fine and gross motor delays, passivity, postural instability, hypotonia, and atypical motor behaviors.24, 26 Other studies, in which infant SIBS-A have not yet been assigned an outcome diagnosis, indicate that variations from typical development might appear by 6 months of age and might include difficulty shifting attention in novel contexts,27, 28 late onset of babbling and motor milestones,29 and, possibly, decreased gaze towards faces and impaired affect regulation30, 31 (but see Merin et al.'s negative findings with 6-month-olds32). Research is underway in several laboratories to determine whether the presence of these and other characteristics during the first 6 months of life are predictive of ASDs or related, milder disorders.

The literature reviewed above and data from my own laboratory suggest that, during the first 9 months of life, signs of developmental disruption are variable across the child population and might even be absent altogether in some infants later diagnosed with an ASD.24, 26 Signs of abnormality might manifest even if the developmental quotient falls within normal limits24, 25 on standardized developmental tests such as the Mullen Scales of Early Learning.33 The consistent presence, particularly in combination, of behaviors such as those described above and in Table 1, warrant referral and developmental surveillance, as they might be precursors to an ASD or to other non-ASD developmental disorders.

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Early behavioral indicators of autism spectrum disorders

From the first birthday onwards, behavioral indicators of ASD become increasingly identifiable and can be used to differentiate toddlers with ASDs from those with other developmental delays or typical development. These indicators, as identified in the retrospective and prospective literature, are aligned with the three categories of behavior associated with the diagnostic criteria for an ASD within the DSM-IV®:1 qualitative impairment in social functioning, qualitative impairment in communication functioning, and the presence of stereotyped and repetitive patterns of behavior and interests (Table 1). Although repetitive and stereotyped patterns of behavior and interests occur in disorders other than ASDs, comparisons among 2-year-olds with ASDs, developmental delay, or typical development revealed that the presence of several different repetitive behaviors within the same child might be an indicator of an ASD, especially if social and communication skills are abnormal.34 In this study, parents of children with ASDs did not, however, report more self-injurious behavior, sensitivity to noise, or resistance to trivial changes in the environment than did parents of children with developmental delay or typical development.34

Patterns of onset and developmental trajectory

Data from two prospective, longitudinal studies25, 35 suggest that there are several different onset patterns of ASD. In some children, multiple signs of ASD, particularly impairments in social functioning and communication, are present by 14 months of age to such a degree that an expert in early child development and autism might consider a diagnosis of ASD. Development in these children is slow, at least in the social domain.35 Around a third of toddlers judged to have an ASD near the time of their first birthday are likely to exhibit instability with regard to the presence of ASD-related behavior, and diagnostic impressions might shift from an ASD at the time of the first birthday to a non-ASD by the third birthday.36 Similarly, Turner and Stone's report from 200737 indicated that 68% of 2-year-olds who meet the diagnostic criteria for ASD fail to meet such criteria at 4 years of age. The majority of children with an unstable diagnosis of ASD were younger than 30 months of age at the time of the first diagnosis, had higher cognitive functioning than 2-year-olds with a stable diagnosis of ASD, or both.37 Sutera and colleagues have reported similar findings.38

In other children, clear signs of ASDs are not present until later in the second year of life, or even until the third year.19, 35, 39, 40, 41 These children might have mild signs of developmental disruption at 14 months of age or might even seem to be developing normally, but they gradually become less socially engaged after 14 months of age.35 Regardless of the pattern of onset, any child with an ASD can show regression, in which existing skills, particularly spoken language35, 36, 39, 42 and social–emotional reciprocity,35, 42 are diminished or lost altogether, and atypical patterns of behaviors might emerge (e.g. temperamental and sensory dysregulation or repetitive and stereotyped patterns of behavior and interests).26, 35, 36 Regression, as described in the retrospective literature, occurs in 10–50% of children with autism, at a mean age of 19 months,42 and usually involves a loss of language skills.42 Language regression in autism does not rule out the possibility of the acquisition of language skills later in life; nor does it predict a more severe impairment in language skills.43

The heterogeneous nature of ASDs means that multiple etiologic factors can be anticipated. Despite anecdotal reports to the contrary, a large, collaborative, retrospective study found no evidence that regression in ASD is associated with the measles–mumps–rubella (MMR) vaccine.42 Importantly, variations in the timing of MMR vaccinations were not related to variations in the timing of regression.42

The evidence to date indicates that genetics have a major role in the etiology of ASDs, with an additional role for environmental influences that are yet to be defined.44, 45 Although the neurobiological basis of ASDs is still poorly understood, some intriguing recent findings have provided the impetus for the development of new etiologic hypotheses. One such finding is overgrowth of the brain in infants with ASDs (on the basis of group data), particularly between 6 and 12 months of age; this timing parallels the onset of clinical signs of developmental disruption in some children with ASDs. Although the head circumference of children with ASDs does not differ from the norm at birth,46, 47 brain growth accelerates abnormally in some children with ASDs, beginning some time between 6 and 12 months of age and leading to macrocephaly.48, 49, 50 Hazlett and colleagues reported a generalized enlargement of the gray and white matter in the cerebrum in a group of 2-year-old children with ASDs compared with control children with typical development or developmental delay.49 In a small autopsy study, evidence of neuroimmune activation, including activation of neuroglia and elevated levels of cytokines in brain tissue and the cerebrospinal fluid, was reported in individuals with ASDs.51, 52 This neuroimmune activation is an endogenous process (occurring within the brain) that might result from disordered brain development and probably does not have an exogenous cause.51, 52 Such activation could have an important role in synaptic plasticity and modeling of neuronal networks that influence behavior and cognition.53 The presence of an abnormal pattern of brain growth in ASDs, in addition to abnormalities in cortical and white matter cytoarchitecture,54 suggests that late stages of neuronal organization are disrupted, although gross neuroanatomical abnormalities of the brain are rarely detected on clinical anatomical MRI.55

The findings reviewed above, combined with evidence from the retrospective literature on developmental regression in ASDs, support the recommendations put forward by the American Academy of Pediatrics.56, 57 These guidelines recommend developmental surveillance at every well-child preventative care visit, with developmental screening at 9, 18, and 30 months of age and autism-specific screening at 18 and 24 months of age. They also provide recommendations with regard to referral and evaluation of children suspected of having an ASD. In addition, a set of medical tests for children with suspected ASDs has been proposed by the American Academy of Neurology.55

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Caveats of early detection

Screening tools for ASDs, such as the Early Screening of Autistic Traits Questionnaire,58 the First Year Inventory,59 and the Modified Checklist for Autism in Toddlers (M-CHAT),60 are available for use beginning at 12–16 months of age, but the validity of these instruments in children within this age range has not been established in large populations. Studies that used the Checklist for Autism in Toddlers (CHAT)61 or the M-CHAT have focused on children aged 18–30 months.62 Initial data on these instruments suggest that they have low sensitivity in the general population (many false-negatives) but good specificity. Recent studies of the M-CHAT, which takes 5–10 min for parents to complete and 5 min to score, estimated that the sensitivity falls within the 75–91% range.62, 63 The sensitivity of the M-CHAT is strongest if used in a clinical setting or with children referred owing to developmental concerns.62

Primary care providers must balance screening results against parents' perceptions of their child. In cases in which parental concerns are substantial, are perceived to interfere with the parents' interactions with their child, or are expressed about multiple aspects of development, referral to the local public early intervention program (e.g. Part C providers) is appropriate. Second-stage screening tools, such as the Screening Tool for Autism in Two-Year-Olds64 or the Pervasive Developmental Disorders Screening Test-II,65 are also available to help differentiate children with ASDs from those with other disorders; these tools are designed for children aged 24 months or older. The sensitivity and specificity of these measures are still under investigation.

Two issues that arise with ASD screening are false-positives and false-negatives. Strategies aimed at decreasing false-positives, such as conducting a brief interview with parents if their child's score on an ASD-specific screening tool raises suspicions about an ASD, are considerably improving the positive predictive value of ASD-specific screening tools.60 False-negatives are more of a problem and can arise for numerous reasons. One reason is that many screening tools for ASDs use the terminology 'lack of' for behaviors, such as pointing, that are expected in typically developing toddlers, but are often abnormal in children with ASDs. Most toddlers with ASDs do, however, exhibit these behaviors, albeit less often, with less diversity and flexibility, less well coordinated with other behaviors, such as gaze, vocalization, or smiling, and for less duration within an interaction, than in typically developing children.35, 66 Parents, therefore, fail to endorse the item, and the child might pass the screening test, despite having abnormalities. Furthermore, parents might not report key autism-related behaviors in their infants and toddlers, particularly those involving subtle impairments in social functioning.11, 67 Another possible reason for false-negatives is the, often gradual, progressive nature of ASDs, which underlines the need for repeat screening in some cases.35, 56

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Stability of early diagnosis of an autism spectrum disorder

Although ASDs can be detected by 14 months of age in some children,35 there is less stability of symptomatology, and hence in diagnosis, at this age than later in development. Nevertheless, children who met our preliminary criteria for ASDs at 14 months of age, but not at 36 months of age, usually exhibited another type of impairment at 36 months of age, most often impairment in social communication.36 Two reports indicate that by 20–21 months, the short-term stability of the diagnosis is high.11, 39 At least six studies have reported that, in most cases, the diagnosis of an ASD made during the third year of life (although most of the children studied were actually nearing their third birthday) remained stable during follow-up periods ranging from 1 to 7 years.68, 69, 70, 71, 72, 73 Two recent reports, however, provided more conservative estimates of the stability of the diagnosis of ASD in 2-year-olds.37, 38 These reports indicated that the greatest instability of the diagnosis was observed in children younger than 30 months of age at diagnosis and/or who had relatively high levels of cognitive functioning.37 Diagnostic shifts within or off the autism spectrum over the course of 2–7 years occur more often in children diagnosed with PDD-NOS at 2 years of age than in those diagnosed with autism at 2 years of age.38, 70 Despite these reports, Sutera and colleagues38 reported that nearly 22% of the 2-year-olds diagnosed with an ASD in their sample no longer had a diagnosis of an ASD at 4 years of age. Between the ages of 2 and 7 years, there is considerable variability in the severity and nature of symptoms in children with ASDs.68 In addition, expert clinical judgment, whereby information from a variety of sources is considered, is more reliable than a diagnosis made only on the basis of a standardized assessment instrument for autism or by a less experienced clinician.72, 74

Prediction of the outcome for young children with ASDs is not straightforward. Standard assessments of autism at the age of 2 years did not predict functioning at 7 years of age, even within the same domain of social functioning, communication, or repetitive and stereotyped patterns of behavior and interests, but assessments made at 3 years of age did predict behavior at the age of 7 years.68 Children whose diagnosis moved off the autism spectrum between the ages of 2 and 4 years tended to show better motor skills, an increased ability to sit and listen to a story, and a greater desire to please their parents at the age of 2 years than those whose diagnosis remained within the autism spectrum; however, neither the symptom severity nor the cognitive level at 2 years of age was useful for prediction of who would fail to meet the criteria for an ASD at the age of 4 years.38

The literature reviewed above indicates that the prognosis is uncertain for children diagnosed with an ASD before 3 years of age. Rather than attempting prognostic statements for very young children who are thought to have an ASD, clinicians should, therefore, focus on instituting appropriate intervention and establishing systematic follow-up to evaluate developmental progress and assess etiologic bases as new information appears in the literature about diagnostically fruitful medical tests and treatment for ASDs.

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Evidence to support early intervention

Most of the literature on the efficacy of intervention for ASDs in preschool-aged children focuses on behavior-based interventions. In general, preschool-aged children with ASDs have positive responses to intensive interventions (greater than or equal to20 h per week) that target a wide range of skills. An average gain in IQ of 20 points has been noted following interventions involving applied behavior analysis (ABA) that are based on operant conditioning, in which discrete skills are taught by use of massed trials conducted outside the natural context.75 Similar improvements have also been noted in developmentally based interventions, in which objects and activities of the child's interest form the basis of many teaching interactions and in which teaching often occurs within the natural context.76, 77 More-naturalistic applications of ABA, such as in Pivotal Response Training,78 have also been shown to be effective for teaching important social and communication skills to young children with ASDs.79, 80 Such applications of ABA emphasize the use of child-selected activities to increase the child's motivation and generalization of skills, flexible teaching of multiple skills within a single activity, use of natural and meaningful rewards, and child initiation of play with toys and interaction with people. Other developmental approaches (e.g. the Floortime81 or Social Communication, Emotional Regulation, and Transactional Support82 models) are characterized by multimodal integration of sensory stimulation, child-selected play-based reciprocal interactions, use of visual teaching aids, and family involvement to emphasize goals of developing social communication, social reciprocity, and affective and self-regulation skills. Studies of the efficacy of these intervention approaches are in progress. In view of the fact that ASD is a heterogeneous disorder that affects multiple systems, and that children with ASDs have different needs at different points in their development, it is unlikely that a single method of intervention will be optimally sufficient for all children with these disorders.83, 84

Guidelines for early intervention85 recommend that a combination of direct intervention and stimulation within natural routines should be administered on an intensive basis for children with ASDs. Although the term 'intensive' has not been empirically defined for toddlers with ASDs, the number of hours of speech–language therapy received between the ages of 2 and 4 years by children with ASDs is related to their development of spoken language.86 In general, improvement might be proportional to the number of hours of intervention per week.87, 88 For preschool-aged children with ASDs, the National Research Council has recommended 25 h per week of therapy-based engagement, which can be delivered by therapists, family members, and other caregivers.85 The literature has shown that caregivers who are trained to recognize signs of a child's comprehension and attempts to initiate interaction or communication can have a marked impact on the child's development,89 and manualized approaches are available to teach caregivers such skills.90

A combination of home-based and center-based intervention is proving to have a beneficial impact on the development of 2-year-olds with ASDs. A randomized clinical trial showed that intensive engagement, involving classroom-based intervention for 10 h per week paired with caregiver training, was associated with robust improvement in cognitive, language and social functioning over a 6-month period.91 A combination of intervention methods was used, including discrete-trial teaching based on operant conditioning to prime new skills, Pivotal Response Training92 to stimulate concept-based functional skills in a natural context, input and output augmentation to assist learning through visual aids, sensory–social routines to heighten attention, environmental engineering to increase predictability and facilitate transitions, joint action routines to promote social engagement, and communication temptations to increase motivation to communicate.91 Other studies, some involving parent-mediated intervention93 and some involving interventions delivered by therapists,80, 94, 95 also showed that imitation, joint attention, language, play, and affect sharing can be greatly improved in children with ASDs and these improvements might be sustained in the long term. Early intervention in young children with ASDs might reduce impairments in social and communicative skills that interfere with their ability to elicit and sustain social engagement with others and limit their moment-to-moment learning opportunities. Early intervention might, therefore, interrupt an otherwise possibly devastating cascade of events associated with social isolation and maladaptive behaviors. Early detection and appropriate intervention might prevent a decline in social functioning and decelerated language functioning between 14 and 24 months of age35 and prevent development from reaching a plateau between 2 and 3 years of age.11

Although many children with ASDs will show a moderate to high improvement in response to intensive early intervention, other children might show a limited improvement. Factors such as the pretreatment IQ,96, 97, 98 social interest,75, 83 language functioning,75 age at entry into the intervention,4, 97, 98 and the rate of initial learning99, 100 have been reported as predictors of outcome.

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Conclusions

Much ongoing research is focused on early predictors and characteristics of ASDs. Current scientific thinking indicates that, in the majority of cases, behavior-based clinical signs of ASDs begin to emerge most clearly between the first and the second birthdays. These signs will involve abnormalities in social and communication responsiveness and initiative, which can occur with or without spoken language or mental retardation. Repetitive and stereotyped patterns of behavior can also occur, and might become increasingly intense or frequent, in the first 3 years of life. Some children with ASDs will have a period of development during which signs of developmental disruption will be subtle or absent. Screening for ASDs should, therefore, begin by 18 months of age and be repeated at 24 and 36 months of age. The diagnosis of ASD becomes increasingly stable over the first 3 years of life. Detection of an ASD-related behavioral profile is possible as early as the first birthday and warrants enrollment in an intervention. Early intervention should address a comprehensive range of skills and involve a mixture of parent-mediated and therapist-mediated interventions. An emphasis should be placed on development of social and communicative abilities within natural settings.

Key points

  • Early signs of autism spectrum disorders (ASDs) include infrequent social orienting, infrequent initiation of social engagement, poorly sustained and coordinated engagement with others, a limited variety of gestures and other forms of communication, and repetitive motor behaviors
  • Development of siblings of children with ASDs and other groups at high risk of ASDs should be followed closely from 6 months of age onwards
  • Diagnosis of ASDs becomes possible at 14 months of age, but the diagnosis might be unstable in up to a third of children diagnosed before 30 months of age
  • Young children with ASDs show improved social, communication, language, play and cognitive functioning when they are enrolled in a developmentally appropriate intensive intervention

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Acknowledgments

This work was supported by grants MH59630 and MH066417 from the NIH, Bethesda, MD, USA, which were awarded to the author. Désirée Lie, University of California, Irvine, CA, is the author of and is solely responsible for the content of the learning objectives, questions and answers of the Medscape-accredited continuing medical education activity associated with this article.

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