Abstract
Introduction
Many clinicians working with toddlers and preschool-aged children have faced the dilemma of whether to defer diagnostic decision making in children with complex and rapidly changing ability profiles or providing a possibly inaccurate diagnosis that at least enables these children and their families to access intervention and education programs. The current study reports on the complexity inherent to early diagnostic decision making as it examined the predictive value of early abilities on later diagnosis in young, clinically referred children with language difficulties.
The complex behavioral profiles of young children with developmental difficulties
Early childhood is characterized by periods of accelerated growth and relative stability which complicates the differentiation between normative variation and atypical development (Carter et al., 2004; Egger & Angold, 2006). Moreover, if children present with problems early in life, these can be indicative of several neurodevelopmental disorders. Nevertheless, these children are often referred to specialists or specialized services with expertise in one developmental domain or one specific neurodevelopmental disorder. They often only focus on the child’s difficulties which are most obvious. Additional difficulties may, therefore, go unnoticed and children with similar ability profiles may be diagnosed differently depending on the educational background and the expertise of the clinician seen (Gillberg, 2010).
Language difficulties readily attract attention and are among the first concerns of parents of children later diagnosed with a neurodevelopmental disorder (Kozlowski et al., 2011). Hence, the heterogeneity among these children is used to illustrate the diagnostic complexity in young children with developmental difficulties.
The example of young children with language difficulties
Young children with language difficulties do not only differ with respect to the type and severity of their language difficulties but also with respect to the presence of co-occurring problems and their development over time (Desmarais et al., 2008). Several studies, found that children with language difficulties can present with co-occurring motor deficits (Finlay & McPhillips, 2013), limited nonverbal cognitive abilities (Buschmann et al., 2008), limited symbolic play capacities (Rescorla & Goossens, 1992), problem behavior (Henrichs et al., 2013), and/or problems in social relationships (Mok et al., 2014).
Results of longitudinal studies indicate that the majority of young children with language delay catch-up with their peers, though some continue to show language difficulties over time (e.g., Dale et al., 2003; 2014). Predicting the risk of persistent language difficulties from children’s early abilities is difficult. Risk factors include a family history of language delay, limited use of alternative (nonverbal) communication strategies, and the presence of receptive as well as expressive language difficulties (Ellis & Thal, 2008). Language difficulties can also be an early marker of neurodevelopmental disorders other than a language disorder (LD), with autism spectrum disorder (ASD) and intellectual disability (ID) being particularly common (Ek et al., 2012; Miniscalco et al., 2006).
According to the DSM-5, LD is diagnosed when the individual has persistent difficulties in language comprehension and/or production and does not demonstrate age-appropriate language ability (American Psychiatric Association, 2013). In the current study, ‘persistent’ was defined as language difficulties despite language intervention. A large longitudinal study showed that it is difficult to diagnose LD before the age of five (Stothard et al., 1998).
Core symptoms of ASD include impairments in social-communication as well as the presence of restricted and repetitive behaviors and interests (RRBIs) (American Psychiatric Association, 2013). The overlap between ASD and LD has received considerable attention over the past few decades and tend to be most noticeable in the social-communication domain (Leyfer et al., 2008). Nevertheless, previous studies found hyper- or hyposensitivity reactions (Taal et al., 2013) as well as the presence of motor stereotypies (Goldman et al., 2009) in some children with LD. ASD is often diagnosed, on average, around the age of four years, although an earlier diagnosis is possible as well (Brett et al., 2016). Variable results have been found in studies on the stability of an early ASD diagnosis (Woolfenden et al., 2012; Zwaigenbaum et al., 2016). However, studies on diagnostic stability of for example LD or ASD often only focus on one diagnostic category. Therefore, these studies do not take into account the difficulties of early differential diagnostic decision making and stability across different diagnostic categories over time.
Below-average cognitive abilities and impairments in adaptive behavior are the core symptoms of ID (American Psychiatric Association, 2013). Below-average cognitive abilities are often part of the ability profiles of many children with language difficulties (Buschmann et al., 2008). Although cognitive abilities tend to be relatively stable in typically developing children (Heller et al., 1996), they may be more variable in children with language difficulties (Benasich et al., 1993) and in children with ASD (Dietz et al., 2007).
Aim of the study
Clinicians do experience challenges and uncertainties in early diagnostic decision making (Charest et al., 2019; McDonnell et al., 2019). Young children with developmental difficulties often develop rapidly and present with symptom patterns that can be indicative of several disorders. In the current paper we do not make any statements about which condition is causing another condition. Based on the DSM-5 criteria for LD, ASD, and ID, children may present with only LD, ASD or ID, or several condition may co-occur in one child, such as LD and ASD or ID and ASD. A diagnosis of LD is not possible when an ID is present. This paper focuses on how to distinguish between those different conditions in young children referred with language delays and how these classifications evolve over time. Early and accurate identification and diagnosis are important to facilitate access to intervention and to increase chances to positively influence developmental trajectories (e.g., Hampton & Kaiser, 2016; Walker et al., 2020).
In this exploratory study, a group of young children referred with language difficulties has been followed over a time period of four years. This study examines (1) whether an early diagnostic classification of ID, ASD and/or LD at Time 1 is stable when compared to a best-estimate (BE) diagnosis established four years later, and (2) whether early symptoms of ID, ASD, and LD at Time 1 correctly predicted later BE diagnosis.
Methods
Participants
At Time 1, the sample included 36 two-to four-year-old monolingual Dutch speaking children with language difficulties. The sample included 30 boys and 6 girls with a mean age of 33.36 months (
One year later, all children were invited for follow-up assessment in order to track their development over time. Additional follow-up appointments were scheduled depending on the children’s needs. We did, therefore, not have the same amount of data over a similar time frame for all children. Four years after Time 1, the first two authors - who were trained as clinicians and have several years of experience in assessing neurodevelopmental disorders in young children - reviewed the clinical files of all children of the original sample, including reports on developmental and medical history, test results, multidisciplinary diagnostic reports, and speech and language intervention reports. The second (but not the first author) was unfamiliar with all participants. Children were included in the current study if they made at least one return visit in the four years after Time 1 and if sufficient information was available to establish a best-estimate (BE) diagnosis for each of the three neurodevelopmental disorders of interest (see Table 1). Based on these criteria 14 children were excluded.
Criteria per level of diagnostic confidence for each of the three diagnostic categories.
FU = follow-up; LD = language disorder; ASD = autism spectrum disorder; ID = intellectual disability; pc. = percentile; DLD = developmental language disorder; ADOS = Autism Diagnostic Observation Schedule.
The final sample included 22 children (17 boys, 5 girls) with a mean age of 72 months [6 years] (
Establishing a BE diagnosis
Based on DSM-5 classification criteria (American Psychiatric Association, 2013), the diagnostic categories of LD, ID, and ASD were divided into four levels of diagnostic confidence: not applicable versus possibly, probably, or definitely applicable. Criteria for each level of diagnostic confidence were established in advance (see Table 1) and both raters independently completed a BE diagnosis form. BE diagnoses were based on follow-up data. With respect to the diagnostic category of ASD, however, Time 1 qualitative descriptions - but not the cut-off scores - from the Autism Diagnostic Observation Schedule (ADOS: Lord et al., 1999) and the Diagnostic Interview for Social and Communication Disorders - 11th edition (DISCO-11: Wing, 2006) were made available. This allowed the raters to take the presence of ASD-related characteristics in the past into account as - according to DSM-5 criteria - the onset of the symptoms characterizing this disorder is in the early developmental period (American Psychiatric Association, 2013). Children who presented with clinical signs at Time 1 and an ADOS score above the ASD-cut-off at follow-up qualified for diagnosis as did children who received a clinical diagnosis of ASD.
There was complete agreement between the raters, except for one child for whom consensus was reached after joint review of the information available. A BE diagnosis of LD, ID, or ASD was established in probable or definite cases only. With respect to LD, care was taken to ensure that only those children with persistent language difficulties qualified for diagnosis which was operationalized as below-average receptive and/or expressive language abilities at two (or more) time-points despite intervention. Following DSM-5 criteria, a BE diagnosis of LD was not made if children met criteria for a BE diagnosis of ID.
Instruments used at time 1
As a BE diagnosis of LD, ID, or ASD was predicted from children’s abilities at Time 1, the instruments that were used to assess their abilities at that time are reported below.
Ethical considerations
Parents received information on the content of the study and provided written informed consent. The design of the study was approved by the medical ethical board of the University Hospitals UZ/KU Leuven.
Data analyses
Language and nonverbal cognitive mental age equivalent scores were converted into language and developmental quotients that provide an age-dependent estimate of the magnitude of the delay. Pearson’s chi-square tests were used to examine the relationship between cluster membership at Time 1 and BE diagnosis at follow-up. Binary logistic regression analysis was conducted to examine whether early symptoms of LD, ID, and ASD at Time 1 correctly predicted later diagnosis. This technique enables the prediction of a categorical outcome from one or more continuous predictor variables which do not need to be normally distributed (Williams et al., 2013). Although the sample size in this study is smaller than generally recommended, the data met the assumptions for binary logistic regression analysis: (1) linearity of the logit, (2) the absence of multicollinearity (correlations between predictor variables < .71; variance inflation factors < 10), and (3) the independence of errors. Standardized residuals were checked to ensure that none of the children exerted an undue influence on the regression models. None of the children had absolute values above 2.5 and no more than 5% had absolute values above 2. In each of these case the value of Cook’s distance was below one and the leverage values were in the expected range. Therefore, these children did not seem to have a large influence on the regression models (Stevens, 2002) and were included in the analysis.
Results
After a multidisciplinary clinical assessment at Time 1, ten children received a clinical diagnostic classification of ID, ASD, or both (see Figure 1). For some children (

BE diagnosis at follow-up compared to clinical diagnosis at Time 1.
Four years later, 19 (86%) of the 22 children who participated in this study, received a BE diagnosis of ID, ASD, and/or LD, with ASD being most common (
Information on the stability and change in diagnosis from Time 1 to follow-up is depicted in Figure 1. In only five cases (23%) clinical diagnosis or the combination of two diagnoses at Time 1 remained exactly the same at follow-up. Ten children (45%) received a new or additional diagnosis at Time 2. Three children (14%) switched diagnostic categories and in two cases (9%) a diagnosis was withdrawn. A diagnosis of ASD at Time 1 turned out to be more stable at follow-up (9 out of 11 children with a (possible) ASD diagnosis at Time 1) compared to a diagnosis of ID (4 out of 7 children with an ID diagnosis at Time 1). However, more children received a later ASD diagnosis at Time 2 without being diagnosed at Time 1 (7 new diagnoses) compared to ID (1 new diagnosis).
Predicting a BE diagnosis of LD
A BE diagnosis of LD was established in 7 of the 22 children. Five of the children in the LD subgroup also received a BE diagnosis of ASD. The receptive and expressive language quotients at Time 1 (Table 2) did not differ significantly between children with and without a BE diagnosis of LD (receptive language:
Means (and standard deviations) for predictor variables per BE diagnosis at follow-up.
The adapted regression model significantly predicted children’s diagnosis (model χ2(2) = 6.82,
Binary logistic regression analysis: Predicting the odds of obtaining a BE diagnosis of LD, ID, or ASD at follow-up.
Predicting a BE diagnosis of ID
Five of the 22 children received a BE diagnosis of ID at follow-up. Four of the children in the ID subgroup also received a BE diagnosis of ASD. The children with a BE diagnosis of ID had a lower developmental quotient than their non-ID counterparts at Time 1 (Table 2) which indicated a significantly greater impairment in nonverbal cognitive abilities (
Predicting a BE diagnosis of ASD
A BE diagnosis of ASD was established in 16 of the 22 children. Some of the children in the ASD subgroup also received a BE diagnosis of ID (
A binary logistic regression analysis was performed to examine whether children’s ADOS or DISCO domain scores at Time 1 predicted a BE diagnosis of ASD at follow-up. In order to limit the number of predictor variables included in the regression model, analysis were performed separately for each diagnostic instrument. Neither model resulted in an accurate prediction of children’s diagnostic status (ADOS model χ2(2) =1.31,
Discussion
Young children with language difficulties form a heterogeneous group, not only with respect to the type and severity of their language difficulties but also with respect to the presence of co-occurring problems and their development over time. This exploratory study examined in a group of clinically referred children with language difficulties whether BE diagnosis at follow-up was related to early clinical classification at Time 1 and if early symptoms of ID, ASD, and LD correctly predicted later diagnosis.
Stability of early diagnostic classification in young children with language difficulties
For most of the participating children, a clinical diagnosis was established only after repeated, multidisciplinary biopsychosocial assessment and not at the age of first referral. Moreover, many of the children who did receive a clinical classification at Time 1, switched diagnostic categories or received an additional diagnosis over time. Based on the comparison between diagnosis at Time 1 and at follow-up, early diagnostic classifications in young children referred with language difficulties seem to be rather unstable before the age of four.
At follow-up, a best-estimate (BE) diagnosis of LD, ID, or ASD was established in approximately 86% of the children. BE diagnosis and clinical diagnosis at follow-up corresponded in the majority of cases. As we do not have data on the representativeness of our sample for all children who visited the collaborating outpatient centers, it may be possible that parents who chose to participate had more or different concerns about their child’s development than non-participants. This, in turn, may have contributed to the high rates of neurodevelopmental disorders found within the sample. Previous studies, however, also found high rates of neurodevelopmental disorders in children previously diagnosed with language difficulties (Ek et al., 2012; Miniscalco et al., 2006; 2018).
Predicting children’s BE diagnosis from their early abilities
There was a significant relationship between the magnitude of children’s receptive language delay at Time 1 and a BE diagnosis of LD at group level, though some children with severe receptive language difficulties at Time 1 showed (near) average linguistic abilities at follow-up. Clinicians who identify children with language difficulties have the difficult task of deciding whether or not intervention is necessary to ameliorate the established problems. Language pathways are fluid and the majority of children will spontaneously catch-up with their peers before entering primary school (Dale et al., 2003). Some, however, continue to experience language difficulties and these children should access intervention programs as early as possible. The intervention model for children with language difficulties described by Ebbels et al. (2019) offers clinicians a stepwise approach of language intervention with increasing levels of intensity and individualization based on the child’s needs to facilitate clinical decision-making. With regard to diagnostic classification, only children with persistent language difficulties should receive a diagnosis of LD (American Psychiatric Association, 2013). DSM-5, however, offers no criteria to determine ‘persistency’ which may be thought of as below-average receptive and/or expressive language abilities at at least two time-points despite intervention.
The magnitude of children’s nonverbal cognitive delay at Time 1 was a significant predictor for a BE diagnosis of ID at follow-up. Although nonverbal IQ scores appeared to be relatively stable at group level, some children showed a considerable drop in IQ scores over time whereas others moved from the below-average to the average ability range. Although nonverbal IQ tests are frequently used, it remains unclear what these tests are exactly assessing for children with language difficulties (Gallinat & Spaulding, 2014). Although limited abilities in both the language and cognitive domain may have a shared etiology, alternative explanations should be considered as well. As the difficulty of test-items increases, the performance of children with language difficulties may be hampered by: (1) a limited understanding of the verbal instructions that often accompany an examiners nonverbal behavior and (2) less developed self-directed speech which enhances the performance of typically developing children in novel problem solving tasks (Gallinat & Spaulding, 2014; Lidstone et al., 2012). Increased language proficiency and on-task behavior, on the other hand, may account for the rise in some children’s IQ scores over time.
Children with ASD were overrepresented in the current sample as a BE diagnosis of this disorder could be established in almost 75% of the children. Language development is delayed as well as deviant in many preschool-aged children with ASD (Boucher, 2012) and language difficulties have been part of the diagnostic criteria up to DSM-IV-TR. DSM-5, however, has listed language impairment as a specifier which should inform treatment planning. In this study, early symptoms of ASD within the social-communication and behavioral domain were assessed by means of an interview schedule as well as direct observation. Although children in the ASD subgroup scored somewhat higher on indices of both instruments at Time 1, the presence of the disorder could not be predicted from children’s social-communication problems nor the presence of RRBIs. This may be due to unequal subsample sizes though the possibility of behavioral overlap between the ASD and non-ASD group should be considered as well. This became particularly salient as three children who did not receive a BE diagnosis of ASD scored above the ASD cut-off on the ADOS at Time 1.
Many children with language difficulties experience social problems which can persist over time (Mok et al., 2014) and may resemble the problems of children with ASD on standardized clinical measures for ASD symptoms, such as the ADOS. Some individual behaviors, however, tend to discriminate between children with and without ASD as the former seem to be less inclined to initiate and engage in reciprocal social interactions (Mildenberger et al., 2001; Ventola et al., 2007), and show more socially withdrawn behavior compared to children with LD (Richard et al., 2019). This was supported by the results of the current study as parents of children with a BE diagnosis of ASD reported higher levels of impairment on DISCO items assessing social-emotional reciprocity.
The children with and without a BE diagnosis of ASD did not differ significantly on the RRBI domain of either the ADOS or DISCO in this study. RRBIs encompass both lower- (e.g., motor stereotypies) and higher-level (e.g., circumscribed interests, adherence to routines and rituals, and repetitive language) behaviors (Turner, 1999). Young and less verbal children with ASD will mainly display lower-level RRBIs, as these RRBIs require less advanced language and cognitive abilities. These behaviors are also common in typically developing children (Larkin et al., 2017; Leekam et al., 2007) and in children with various other neurodevelopmental disorders (Leekam et al., 2011). The importance of RRBIs as a stable predictor of ASD may increase with age (Camarata, 2014) and/or may be limited to higher-level RRBIs (Honey et al., 2008; Mildenberger et al., 2001). Moreover, it is not only the topography (i.e., types of RRBIs), but mainly the frequency, duration, and/or associated level of impairment that differentiates RRBIs in children with ASD from their non-ASD counterparts (Honey et al., 2008; Leekam et al., 2011; Watt et al., 2008).
The conceptualization of RRBIs as a (multi)dimensional construct ranging into the typically developing child population, questions the validity of social (pragmatic) communication disorder (SCD) as a new diagnostic category in the Communication Disorder section of the DSM-5. SCD is defined by persistent pragmatic difficulties in the absence of other ASD symptomatology in particular RRBIs (American Psychiatric Association, 2013). Nevertheless, children with social communication difficulties are likely to display RRBIs at some point during development (Norbury, 2014). As these RRBIs may not be severe enough to meet the ASD threshold, these children are likely to fall between diagnostic categories.
Limitations and directions for future research
The study was limited by the use of different instruments to measure receptive and expressive language skills and non-verbal cognition, as none of the instruments available covered the variety in the participant’s abilities. Because of the small sample size and the possible overrepresentation of children with persistent and more encompassing developmental problems, the results of this study should be interpreted with caution. Moreover, as the number of and time between follow-up assessments depended largely on the children’s needs, we did not have the same amount of data over a similar time frame for all children. It is important to acknowledge that clinical diagnosis and BE diagnosis are not equivalent as BE procedures force raters to make a decision which in clinical practice may be deferred. Nevertheless, care was taken to ensure that only clinically relevant problems qualified for a BE diagnosis of LD, ASD, or ID. Further research should include a more in-depth examination of the abilities of young children with language difficulties. Attention to motor, behavioral, and affective functioning may reveal important dimensions of functioning and further psychopathology in children with early language difficulties. Moreover, additional research into the validity of the DISCO algorithm for young children is needed as none of the participating children with a clinical diagnosis or BE diagnosis of ASD reached the cut-off. This can be due to limited suitability of the current DSM-5 criteria for young children in general or the selection of algorithm items from the DISCO in particular. Many of the items included in the current algorithm require children to have a certain age or level of language proficiency in order to be met.
Clinical implications
Although parents may present to practitioners with specific developmental concerns, co-occurring problems are likely to be present or tend to develop over time (Gillberg, 2010). Children with developmental difficulties in any domain of functioning should, therefore, be referred for biopsychosocial assessment by an interdisciplinary team. In a biopsychosocial assessment, biological (e.g. gender, physical illness), psychological (e.g., behaviors, emotions) and social (e.g., family background, cultural background) factors that could be contributing to the observed difficulties are taken into account. Parental information as well as assessment and observation in structured and unstructured, more naturalistic situations will result in a holistic picture of children’s strengths and weaknesses in interaction with their environment (O'Keeffe & Macaulay, 2012). An assessment conducted by clinical experts from different disciplines (e.g., speech language therapists, psychologists, pediatricians/child psychiatrists/child neurologists/other medical doctors) offers different perspectives and will avoid ‘tunnel vision’. It is essential that an interdisciplinary team meets to share, integrate, and synthesize information and to provide recommendations for intervention together (Guralnick, 2000). By stating this we do not necessarily argue in favor of a dimensional as opposed to a categorical approach to diagnostic decision making as both have their value. It is the order in which they are used that is of uttermost importance. Dimensional assessment and thoughtful case formulation are a necessary first step. A categorical clinical diagnosis can be established second, if at all (O'Keeffe & Macaulay, 2012).
Many early intervention programs are restricted to children with a specific clinical diagnosis. Such an allocation model assumes that neurodevelopmental disorders can be reliably identified in all children likely to benefit from treatment and that (the families of) children with a clinical diagnosis are in greater need than those without (McDowell & O'Keeffe, 2012). The results of this study indicate that diagnostic classification is often only possible after repeated multidisciplinary, biopsychosocial assessment and not at the age of first referral. Nevertheless, early intervention provides children with enriched experiences, diminishes symptom severity, prevents secondary problems from occurring and enhances sensitive parenting as well as parental well-being (Koegel et al., 2014). These benefits may lead clinicians to err on the side of a false-positive diagnosis in cases of diagnostic uncertainty in order to enable intervention for these children and their families (Skellern et al., 2005). The interrelatedness of diagnosis and intervention seems no longer sustainable (McGorry & Van Os, 2013; O'Keeffe & Macaulay, 2012). Disentangling diagnosis from symptoms and impairments will - although admittedly complex - be a fruitful way forward to ensure early intervention services for children whose clinical phenotype is (still) unclear (Rapee et al., 2012).
Conclusions
This exploratory study revealed some of the complexity inherent to diagnostic classification in young children. Although a clinical diagnosis can be established for some of them, many present with mixed symptom patterns and/or subthreshold symptomatology in a developmental period where intervention is considered most likely to be effective but often requires a clinical diagnosis.
Highlights
Early diagnosis in children with language difficulties seem to be unstable before the age of 4. Language disorder and intellectual disability classifications can be predicted based on early abilities. However, large inter-individual differences were seen in developmental trajectories. A clinical differential diagnosis was established only after repeated assessments.
