Considerations at the base of DSM5 learning disorder criteria - part A

Tannock, R. (2013). Specific learning disabilities in DSM-5; Are the changes for better or worse. The International Journal for Research in Learning Disabilities, 1(2), 2-30.‏

Prof. Rosemary Tannock was a member of the DSM-5 Work-Group for ADHD and Disruptive Behavior Disorders and a Liaison member of the Neurodevelopmental Disorders Work Group to advise on Learning Disabilities.

In this paper she describes the considerations that lead to the decisions that were made regarding LD diagnostic criteria. I'll present her views in black or orange, and thoughts of mine in green.

This post does not "cover" all the aspects the paper discusses, but rather focuses on the things that were interesting to me.  Because of the post's length, it's divided into two parts.  This is part A.

"DSM-5, the fifth edition of the American Psychiatric Association’s Diagnostic and Statistical Manual of Mental Disorders, was published in May 2013, amidst a storm of controversy.  As with the previous versions, this new volume has received strong criticism from the public, individuals with LD and their families, policy makers and well as from clinicians and researchers in the field of mental health.

One of the ongoing concerns was that this version of the DSM continues to reify the concept of ‘discrete disorders’ of the mind, based on various sets of observable signs and symptoms, rather than on specific biological tests or atypical patterns of brain-based states.    However, since scientific knowledge had not yet advanced enough to use neuroscience and genetics to shape the conceptualization of mental disorders in DSM-5, the diagnostic criteria were to remain as behavioral descriptors.

The DSM has a broad influence not only on the diagnosis of mental disorders, but also on how they are perceived by the public, healthcare personnel, employers, and those in the school and judicial systems; how they are funded by medical insurance agencies; how the public policy for mental health is maintained or changed; and how research agendas are set.

Significant changes in diagnostic criteria undermine our ability to rely on research done thus far.  All previous learning disabilities (LD) research was done in light of the old criteria.  Research subjects were divided into LD groups and control groups according to the old criteria, thus conclusions about differences between LD and non – LD persons are valid for people diagnosed in light of the old criteria. 

LD is a "disorder" in DSM5, since medical conditions are called disorders rather than disabilities: ‘Learning Disabilities’ is an educational term.

I still wonder why LD should appear in the DSM and why it is considered to be a "medical condition".

The DSM-5 Manual advises that the diagnostic criteria “are offered as guidelines for making diagnoses, and their use should be informed by clinical judgment.”

The field lacks a complete understanding of LD: instead there are burgeoning descriptions, guises, guesses, hypotheses, and controversies. To date, there is no international consensus as to what constitutes LD, its operational definition (diagnostic criteria), or who can or cannot conduct the required assessment or make the diagnosis.

Early perspectives of LD, in the 1960's, recognized that impaired academic skills (reading, arithmetic) occur in the context of average or even superior intellectual abilities. Other important insights from these early perspectives include the notion that LD (dyslexia) was congenital, heritable, and manifested primarily by males. Underlying cognitive deficits (possible causal factors) focused initially on visual problems. For example, Hinshelwood (1917) postulated that the primary disability of children with word blindness was in visual memory for letters and words and that it was an inherited condition.

According to the U.S. Federal Law (IDEA, 2004, 20 USC Sec. 1401 (30, SLD), LD is defined as “a disorder in one or more basic psychological processes involved in understanding or using language, spoken or written, that may manifest itself in the imperfect ability to listen, think, speak, read, write, spell, or d arithmetical calculations.”  Thus the notion of underlying deficits in cognitive processing as causal factors was instantiated in the conceptualization of LD.  CHC abilities are of course cognitive abilities and thus a disability in one or more CHC abilities is one of the criteria for LD diagnosis not only according to Flanagan but according to the US federal law as well.

This prevailing legal definition restricts the concept of LD to a language-based disorder, but does not include non-language-based learning difficulties, such as dyscalculia, as defined by some researchers. Motor skills are also not included.  It does seem like language gets in this definition a role more central than it should take.  Difficulties in thinking/reading/ writing/ arithmetic etc. can have many other causes beyond language. 

According to DSM-5, SLD (specific learning disorder) is a type of Neurodevelopmental Disorder that impedes the ability to learn or use specific academic skills, such as reading, writing, or arithmetic, which serve as the foundation for other academic learning. The learning difficulties are ‘unexpected’ in that other aspects of development seem to follow a typical trajectory, or are only minimally delayed. Early signs of learning difficulties may be discernible in the preschool years (e.g., difficulty learning names of letters or to count objects), but they can only be diagnosed reliably after starting formal education.

In DSM-5, SLD is understood to be a chronic condition that typically persists into adulthood, albeit with changes in the way the learning difficulties manifest. In part, this is because adults learn compensatory strategies (e.g., avoid reading by using other media to obtain information or for calculation; use specialized software to assist with reading/writing activities or calculators to assist with numerical activities).  Adults can also use non-technical compensatory strategies like the ability to comprehend what they read despite inaccurate decoding due to better use of general knowledge and deduction skills.

The causes of SLD are unknown, but research suggests the learning difficulties run in families, are heritable, and involve interplay of both genetic anomalies and environmental factors (e.g., prematurity, prenatal exposure to neurotoxins from tobacco, alcohol, street drugs, or other environmental toxins). Neither are the underlying mechanisms of SLD known, although both neural and psychological accounts exist, particularly for difficulties learning to decode words.  Neuroimaging studies have revealed alterations in both structure and function, but it is unclear whether these brain differences are a cause, consequence or correlate of SLD.

A developmental history of Speech Sound Disorder and/or Specific Language Impairment in preschool years is a common precursor of all three LD categories listed in DSM-IV-TR (reading, writing, mathematics), but particularly for poor skills in reading comprehension, spelling, arithmetic fact retrieval, and calculation.  Moreover, one longitudinal study of a community-based sample of children identified with pervasive speech/language disorders in kindergarten were found to have an estimated 3- to 6-fold greater risk for LD (all categories alone or in combination) in young adulthood compared to typically-developing youngsters.

 Longitudinal studies provide strong evidence of a developmental accumulation of learning difficulties with increasing cognitive demands of the curriculum. For instance, children with speech sound disorders in early childhood, later manifest difficulties learning to read, spell, and write in the school years.  Also, over 50% of children with phonologically-based reading difficulties but no apparent difficulties in learning basic arithmetic at age 5 years, manifest learning difficulties in mathematics as well as continued problems in reading at age 7.  However, intervention outcome studies provide no evidence that intervention for one academic domain or its subskills transfer to other academic domains.