Saturday, 29 February 2020

Developmental Language Disorder (DLD) in relation to DSM-5

The tl;dr (too long, didn't read) message in this post is that for all intents and purposes, Developmental Language Disorder (DLD), as defined in the CATALISE project, can be regarded as equivalent to DSM-5 Language Disorder (American Psychiatric Association, 2013). This is a question of interest to people working in systems that require a DSM-5 diagnosis for access to services or insurance payments.

Diagnostic flowchart for CATALISE, based on Figure 1 from Bishop et al (2017).





Figure 1 shows how DLD is defined in the CATALISE project (Bishop et al, 2017). In this framework, DLD is a subset of the broader term 'Language Disorder', with the 'Developmental' prefix used to indicate that the language problems are not associated with a known biomedical condition. The list of biomedical conditions includes brain injury, acquired epileptic aphasia in childhood, certain neurodegenerative conditions, cerebral palsy, oral language limitations associated with sensori-neural hearing loss, autism, intellectual disability and genetic conditions such as Down syndrome.

In DSM-5, 'Language Disorder' is used with a meaning that closely corresponds to DLD. DSM-5 Diagnostic criteria for Language Disorder (category 315.32; F80.2) are as follows:

A. Persistent difficulties in the acquisition and use of language across modalities (I.e. spoken, written, sign language, or other) due to deficits in comprehension of production that include the following: 
  • Reduced vocabulary (word knowledge and use) 
  • Limited sentence structure (ability to put word and word endings together to form sentences based on the rules of grammar and morphology 
  • Impairments in discourse (ability to use vocabulary and connect sentences to explain or describe a topic or series of events or have a conversation) 
B. Language abilities are substantially and quantifiably below those expected for age, resulting in functional limitations in effective communication, social participation, academic achievement, or occupational performance, individually or in any combination 
C. Onset of symptoms is in the early developmental period 
D. The difficulties are not attributable to hearing or other sensory impairment, motor dysfunction, or another medical or neurological condition, and are not better explained by intellectual disability (intellectual developmental disorder) or global developmental delay. 

The relationship between the CATALISE terminology and DSM-5 are shown in Figure 2. In both CATALISE DLD and DSM-5 Language Disorder, cognitive referencing is not used (i.e. there is no IQ cutoff for inclusion in the category), the language problems are seen in early childhood and are persistent and lead to functional impairment, and children with associated biomedical conditions are excluded. 
Figure 2: Set diagram showing relationship between CATALISE and DSM-5 terminology
The CATALISE criteria are more explicit than DSM-5 in relation to bilingual/multilingual children, making it clear that one would not diagnose DLD unless the child showed poor language competence in their best language, but a similar idea is conveyed in the "Differential diagnosis" section of DSM-5, where it is noted that "Language disorder needs to be distinguished from normal developmental variations... Regional, social, or cultural/ethnic variations of language must be considered when an individual is being assessed for language impairment." Unfortunately, a recent account of DLD by a member of the CATALISE panel stated that bilingual/multilingual children were excluded from the DLD category (Rice, 2020). It is unclear how this misunderstanding arose, but it is clearly discrepant with Figure 1.

One might ask why the CATALISE panel decided against alignment with the DSM-5 terminology, given that there is such overlap between CATALISE DLD and DSM-5 Language Disorder. The answer is that "Language Disorder" as defined in DSM-5 is a problematic label because on the one hand it refers to a specific DSM-5 category 315.32 (F80.2), but on the other hand it is widely used to refer to symptom-level problems in many conditions. "Language disorder" is a hopeless term to use in a literature search because it will turn up a far broader range of conditions than those defined by the diagnostic criteria above, including many types of acquired language disorder associated with both developmental and adult-onset conditions.

This broader meaning of the term gives ample scope for confusion. Indeed, even within the DSM-5 manual, ambiguity is apparent. Under "Differential diagnosis" mention is made of Neurological disorders, with the statement "Language disorder can be acquired in association with neurological disorders, including epilepsy (e.g. acquired aphasia or Landau-Kleffner syndrome)". A literal reading of this would mean that, contrary to Diagnostic criteria point D, children with acquired aphasia or Landau-Kleffner syndrome can be regarded as having Language Disorder. I don't think that is what the authors intended: rather they imply that one should differentiate acquired language disorder associated with neurological conditions from "Language Disorder" that corresponds to DSM-5 category 315.32 (F80.2).

In short, in proposing the DLD label, the CATALISE panel were capturing a grouping that is conceptually the same as DSM-5 Language Disorder. We felt, however, that 'Language Disorder" was a problematic label that would generate confusion, and so we used the more traditional term "Developmental Language Disorder" specifically to identify a category of language disorder without associated biomedical conditions.

References
American Psychiatric Association. (2013). Diagnostic and statistical manual of mental disorders (5th ed.). Arlington, VA: American Psychiatric Publishing.
Bishop, D. V. M., Snowling, M. J., Thompson, P. A., Greenhalgh, T., & CATALISE Consortium. (2017). Phase 2 of CATALISE: a multinational and multidisciplinary Delphi consensus study of problems with language development: Terminology. Journal of Child Psychology and Psychiatry, 58(10), 1068-1080. doi:10.1111/jcpp.12721
Rice, M. (2020). Clinical lessons from studies of children with Specific Language Impairment. Perspectives of the ASHA Special Interest Groups, 5(1), 12-29. doi:https://doi.org/10.1044/2019_PERSP-19-00011

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