JCPSLP - March 2018

Developmental Language Disorder

What’s the evidence? Developmental language disorder and non-verbal IQ Natalie Munro and Cori Williams

Clinical scenario A speech pathologist has been asked to run a small group (n = 6) language intervention focusing on vocabulary and morpho-syntax at a local primary school. She checks the children’s case files. All are in their first year of formal schooling. Three of them have been diagnosed with developmental language disorder (DLD) and have non- verbal IQ standard scores over 85. Three other children also have a diagnosis of DLD but their non-verbal IQ scores fall within the 71–84 range – borderline intellectual disability as defined by the Diagnostic and Statistical Manual of Mental Disorders (5th ed.) (DSM-V; American Psychiatric Association, 2013) guidelines. The speech pathologist is familiar with the term specific language impairment , which is predicated on non-verbal IQ within the normal range. She is also aware that the term developmental language disorder has recently been discussed with the aim of including children with language disorder but non-verbal IQ outside the normal range. She wonders whether the children with lower IQ can be considered to have a language disorder. She also wonders whether the two subgroups of children will differ in their response to language intervention. Maybe the children with low non-verbal IQ won’t respond? Maybe they shouldn’t be on her busy caseload? Answerable questions The clinician identifies two key questions, one of which she frames as a PICO question: 1. Should a child with non-verbal IQ below the normal range be considered to have a language disorder or are language skills the result of the intellectual disability? 2. Does a primary school-aged child with DLD and low non-verbal IQ (between 71 and 84) (P) respond to language intervention (I) in the same way (O) as a child with DLD and non-verbal IQ above 85 (all other things being equal) (C)? Search strategy Faced with limited access to research databases, and aware of the recent discussion around the term developmental language disorder, the clinician considers the online resources related to the Raising Awareness of Developmental Language Disorder campaign (#DLD1-2-3 campaign on https://facebook.com/radld.page, Twitter @ RADLDcam, and https://www.youtube.com/radld). She identifies two peer-reviewed, open access articles published by Professor Dorothy Bishop and the CATALISE

consortium (Bishop, Snowling, Thompson, Greenhalgh & The CATALISE consortium, 2016; Bishop, Snowling, Thompson, Greenhalgh & The CATALISE-2 consortium, 2017). These two papers were developed through an online Delphi technique, used to achieve international consensus on key issues surrounding DLD. She is aware that expert opinion does not sit high on the hierarchy of systematic research, but concludes that the papers provide evidence related to clinical practice, an important consideration of E 3 BP (Dollaghan, 2007). The two papers inform clinical practice, and while not official clinical practice guidelines, both indicate that language disorder may occur in children with low non-verbal IQ (Bishop et al., 2016; Bishop et al., 2017). The term DLD is used for school-aged children who present with a persistent language disorder affecting social, emotional and/or academic outcomes, while the term language disorder associated with X – in this case, intellectual disability – would refer to those school-aged children with an intellectual disability and an associated language disorder. Based on these statements, the clinician feels somewhat comfortable that non-verbal IQ should not be considered as part of an exclusionary process for the diagnosis of DLD (as was previously the case for specific language impairment ), but she is not completely confident that she has an answer to the second clinical question. She does note that Bishop et al. (2016) indicate that, in identifying language disorder, a key consideration is “whether the child is likely to benefit from intervention, and that is not determined by IQ” (p. 15). She turns to four references discussed by Bishop et al. (2016) cited to support the notion that the level of non-verbal IQ “does not determine response to language intervention” (p. 15). One referred to a computerised intervention that used acoustically modified speech (a treatment now discounted and not relevant to her practice) and found no treatment effect (Bishop, Adams & Rosen, 2006), while one other focused on preschool children (Cole, Dale & Mills, 1990). The most relevant appeared to be Bowyer-Crane, Snowling, Duff, and Hulme (2011). The clinician was able to locate an abstract of the paper in ERIC (Education Resources Information Centre: https://eric.ed.gov/), but the full paper was not available. From the abstract she finds that the researchers conducted a post-hoc analysis of an earlier RCT (NHMRC Level II evidence) in which young school-aged children received either a phonology with reading (PR) intervention or an oral language (OL) intervention (Bowyer et al., 2008). The intervention was delivered by trained teaching assistants and involved both

Natalie Munro (top) and Cori Williams

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JCPSLP Volume 20, Number 1 2018

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