Early diagnosis of autism spectrum disorder: stability and change in clinical diagnosis and symptom presentation

Autism spectrum disorder (ASD) is a neurodevelopmental disorder characterized by impairments in social communication and interaction, and the presence of restricted and repetitive behaviors and interests. Although evidence suggests that ASD has genetic causes (O’Roak & State, 2008), diagnosis relies on observations of behavioral manifestations. The average age of diagnosis remains well over three (Mandell, Novak, & Zubritsky, 2006), although the American Academy of Pediatrics recommends that all children be screened for ASD much earlier–at 18 and 24 months (Johnson & Myers, 2007). There is a clear need for diagnostic tools and practices for children who screen positive at these young ages. However, because diagnosis in toddlers is relatively new, clinicians face a number of important challenges that warrant further research. The stability of early diagnoses, the utility of diagnostic tools for toddlers, and patterns of symptom change in the first few years of life are among a number of questions critical to professionals making early diagnoses. Stability of Early Clinical Diagnoses of ASD High rates of stability of the broader diagnosis of ASD (rather than specific diagnoses within the spectrum) have been demonstrated in children first diagnosed by age three or older, with estimates ranging from 80 to 100% (see Woolfenden, Sarkozy, Ridley, & Williams, 2012 for a review). However, some estimates for children diagnosed under age three are lower and findings are more variable, ranging from 54 to 100%. While 4 of the 11 studies of children diagnosed with Autistic Disorder or ASD under age three reviewed by Woolfenden and colleagues (2011) reported a 100% stability rate, two studies reported rates under 70% (Stone et al., 1999; Turner & Stone, 2007). In addition to being disparate, these findings may not generalize well to the larger population of toddlers with ASD, as they have consisted of high-risk children (i.e., those with an older sibling with ASD or who are referred because of parental or professional concern), or included only relatively lower-functioning children. Thus, there is a need to examine diagnostic stability in samples screened in the community that yield participants diverse in symptoms and developmental functioning who may not garner parent or professional concern. Findings also need to be extended to younger children, because although children are being screened at increasingly younger ages, just two studies of diagnostic stability have included children under age two. Encouragingly, both studies reported 100% stability for initial diagnoses of ASD (Chawarska, Klin, Paul, Macari, & Volkmar, 2009; Cox et al., 1999). However, neither study reported on stability of children with unclear diagnostic presentations at these young ages. Accuracy of Diagnostic Tools for Young Children Most studies utilize clinical best-estimate diagnoses made by experienced clinicians, a practice that remains the gold standard for diagnosing ASD (Volkmar, Chawarska, & Klin, 2005). However, a standardized observation is crucial to inform clinical diagnosis (Lord & Bishop, 2010). Among the most widely used and validated tools is the Autism Diagnostic Observation Schedule (ADOS; Lord, Rutter, DiLavore, & Risi, 1999). However, it has limited utility with toddlers, as it has unacceptable specificity in children with nonverbal mental ages below 16 months (Gotham, Risi, Pickles, & Lord, 2007). The ADOS – Toddler Module (ADOS-T) was developed to address these limitations (Lord, Luyster, Gotham, & Guthrie, 2012) and demonstrated excellent sensitivity and specificity in the validation study (Luyster et al., 2009). There is a need to examine its utility in other samples as the validation sample included only high-risk children. Of additional importance is the predictive validity of the “ranges of concern,” which its authors recommend to index risk for ASD. While these concern ranges were shown to be largely consistent with concurrent clinical diagnosis (Luyster et al., 2009), their utility in predicting later diagnosis has yet to be examined. Symptom Severity Change in Young Children Another issue critical to the evaluation of toddlers is symptom change within the first years of life, as symptom severity may be more variable than diagnostic status. Clinicians may observe significant changes in the frequency and severity of symptoms as the clinical presentation of ASD unfolds, further complicating early diagnosis. However, existing evidence is still emerging and findings are relatively inconsistent. Improvement of social communication skills, such as joint attention, response to name, and verbal communication, has been reported (Nadig et al., 2007; Sullivan et al., 2007; Yoder, Stone, Walden, & Malesa, 2009), although stability in more global measures of social symptom severity has also been found (Chawarska, Klin, Paul, & Volkmar, 2007). Evidence exists for other trajectories, including plateauing (i.e., developmental slowing) or even worsening (i.e., loss) of these skills in a subgroup of children (Landa, Holman, & Garrett-Mayer, 2007; Lord, Luyster, Guthrie, & Pickles, 2012; Ozonoff, Heung, Byrd, Hansen, & Hertz-Picciotto, 2008). Greater understanding of changes in symptom severity in toddlers would inform studies of diagnostic stability, as changes in symptoms are likely to accompany movement on or off the autism spectrum, but may also be observed in children with stable diagnostic presentations. The purpose of this study was to examine stability of clinical diagnosis and symptom presentation, and the utility of a diagnostic tool in making a clinical diagnosis. The study utilized a prospectively-identified community sample that received a diagnostic evaluation at 15–24 months of age and a follow-up evaluation at least one year later. The specific research aims were to examine the (1) short-term stability of clinical diagnoses, (2) concurrent and predictive utility of ADOS-T classifications and scores, and (3) short-term change in symptom severity.