‘UNLIKELY’ IS THE answer to this question until recently, as pervasive developmental disorders (PDD) have generally been regarded as severe and life-long conditions; however, this does not seem to be the case now. Three lines of research findings may support this view.
The first is that several recent epidemiological studies on PDD or autism spectrum disorders (ASD) reported a higher prevalence of children with PDD/ASD and a higher rate of children with no intellectual disability or even normal intellectual functioning in children with PDD/ASD than previously reported. In 2006, Baird et al. reported that 45% of 158 children with ASD identified in a total population of 56 946 children aged 9–10 years (ASD prevalence, 1.16%) in South Thames, UK had an IQ of 70 or over.1 In 2008, Kawamura et al. reported that 66.4% of 223 IQ-measured children in 228 children with PDD in a total population of 12 589 children aged 1.1–7.2 years in Toyota, Japan had an IQ of 70 or over (PDD prevalence, 1.81%).2 In 2011, Kim et al. reported that 84% of 172 children with ASD identified in the general population of 23 234 children aged 7–12 years in Korea (ASD prevalence, 1.89%) were not intellectually disabled.3 Although these epidemiological studies did not report prevalence by PDD subtype, such a favorable prospect certainly applies to milder PDD subtypes (Asperger's disorder, pervasive developmental disorder not otherwise specified [PDD-NOS] and a part of autistic disorder) but not to severer ones (Rett's disorder and childhood disintegrative disorder). The reason for the recent surge in the prevalence of PDD/ASD, especially of its milder form, is still in dispute. However, the dominant view is the advancement in system and methods to detect children with PDD, especially those with milder impairments who had otherwise been overlooked in older days, although the true rise in the incidence of PDD is not negated.
The second is that some recent studies reported children with PDD/ASD (even though a small minority) who showed satisfactory improvement over time. Turner and Stone reported that 63% of 48 children diagnosed as having ASD at age 2 did not meet ASD diagnostic criteria at age 4.4 Kleinman et al. reported that 15 (19%) of 77 children who were diagnosed as having ASD before age 3 moved off ASD between the ages of 3.5 and 6.8 years.5 Helt et al. reviewed that 3–25% of children with ASD lost ASD diagnosis and achieved a normal range of cognitive and adaptive functioning at follow up.6
And the third is that several studies reported favorable outcomes in young children with PDD/ASD who had received early intervention after early detection. Dawson et al. reported the efficacy of a comprehensive developmental behavioral intervention for improving cognitive and adaptive behavior and reducing ASD severity in 48 children with ASD aged 18–30 months in the first randomized controlled trial.7 Magiati et al. showed the similar efficacy of two early interventions (i.e., home-based early intensive behavior intervention and autism-specific nursery provision) for improving cognitive ability, language, play or autism severity in 44 children with ASD aged 23–53 months in a two-year follow-up study.8
In clinical practices these days, a clinician not infrequently meets a child who definitely meets the diagnostic criteria for some PDD subtype in infancy but does not continue to do so at follow up, even less than a few years later. In that event, the clinician would tell the parents of the child that their child is in partial remission from the PDD subtype if the child does not satisfy the diagnostic criteria for the PDD subtype but has some residual symptoms. And the clinician would tell parents that their child is in full remission from the PDD subtype if the child does not show any symptoms of the PDD subtype. However, we must be cautious about the distinction between full remission and recovery. Full remission means disappearance of clinical symptoms as defined in the diagnostic criteria but recovery requires more (i.e., at least disappearances of clinical symptoms and adaptation disturbances are essential). Although DSM-IV9 has the definitions of partial and full remissions, we need to study the definition and predictors of recovery in view of the recent trend of improving outcomes in PDD.
Nonetheless, with high rates of high-functioning or normally intelligent children with PDD and advancement of early intervention for infants with PDD, clinicians will have increasing opportunities to inform parents of young children with PDD that their children would have favorable outcomes, including full remission or even recovery, which was an unlikely judgment for clinicians last century.