How a child performs in school is important to parents. When a child is not doing well in school, pediatricians are apt to hear of this, as well as whether there have been fevers, aches, pain, or failure to thrive. However, throat cultures, blood counts, and serum liver enzymes rarely correlate with school performance.
Among the causes of academic under performance is a group of conditions labeled by the Federal Government and those in special education as the Specific Learning Disabilities. Too commonly, educators understand these disorders poorly in part because of their medical origin. Pediatricians, on the other hand, are put off by the non-medical labels of educators.
Physicians, and especially pediatricians, have a strong historical and present-day association with this group of learning disorders. The concept of specific learning disabilities grew out of the medical constructs of dyslexia, dyscalculia, and developmental aphasia. Of these three, students with reading disorders were the first to be described in the medical literature. The initial descriptions came from British school physicians and ophthalmologists in the 1890s.1,2 At different times and places, different terms have been used to describe these reasonably bright, occasionally slowspeaking students who read and spell wretchedly despite their best efforts. Congenital word blindness, strephosymbolia,3 developmental dyslexia,4 specific reading retardation,5,6 and childhood dyslexia7 are among the terms used for what appears to be one condition.
It was not clear to early twentieth century doctors why this peculiar disability with reading occurred. It was known that in the affected population boys outnumbered girls, left-handedness or ambidexterity was relatively common, and in some children, speech delay and slow speech into mid-childhood were apt to occur.8 Perhaps because physicians themselves are notoriously poor penmen, the phenomenon of dyslexia remained appealing as an area of medical investigation.
Current trends in medical nomenclature today less frequently make use of the term "dyslexia." When used, the word is often prefixed as "developmental" or "constitutional" or "childhood." "Developmental Reading Disorder" is the official term employed in the American Psychiatric Association's third edition of the Diagnostic and Statistica/ Manna! of Mental Disorders. 9 This DSM-IU classification is widely recognized by health care providers and third-party payers. This same classification system acknowledges developmental disorders in arithmetic and in spoken language whether it be in expressive or receptive spoken language. Syndromes combining the above are considered "mixed" (Table).
Although the term "specific learning disabilities" was coined by educators, its constituent disorders specified as speaking, listening, reading, written expression, and arithmetic are very similar to those given in the DSM-III listing. This coincidence should improve communication between educators and physicians.
An additional category within the DSM-III classification is that of the Attention Deficit Disorders (ADD). Although these disorders are not listed among the learning disabilities, educational underachievement commonly co-exists with ADD. The three subtypes listed by the DSM-Í/I are "with hyperactivity," "without hyperactivity," and "residual" which simply means a persistence of the condition into late adolescence and/or adulthood. Students with underachievement complicated by disorders of concentration or impaired ability to focus their attention are commonly referred for a physician's evaluation. The referring educator seeks the physician's help in reinforcing the diagnosis of a learning disability and inquires whether or not there is evidence for a medically treatable disorder of attention. This commonality of terminology and a mutual need should facilitate a warm relationship between teachers and doctors. Successful control of ADD frequently enhances students' academic performance or, if special services are being provided, facilitates the educational remedial effort. As in other aspects of medical practice, differential diagnosis is an important medical concept. Children who are underachieving in the classroom may do so because of primary emotional disorder, poor nutrition, other organic health disorders, or they may be the victims of inappropriate educational environments.
There are a number of good reasons why the behaviors associated with learning disabilities may be considered biologic in origin18:
(A) Some of the behaviors in isolation or in combination may be seen in young adults or adults who have acquired diseases of the nervous system;
DSM-III Classification of Developmental Disorders
(B) The behaviors or their precursors are evidenced early in life and are relatively persistent throughout the lifetime of the affected individual (but the behaviors, like the individual, may mature also, eg, they evolve with the person);
(C) A slightly higher than expected proportion of individuals with learning disabilities have encountered before, or at the time of birth, some complication of pregnancy and/or delivery;
(D) Many forms of learning disability are associated with a higher than anticipated frequency of similarly affected first-degree relatives, suggesting at least a familial and perhaps a genetic factor;
(E) Electroencephalographic (EEC) derivatives such as Brain Electrical Activity Mapping suggest a variation in physiologic activity in some forms of reading disability which differ from that observed in the achieving population;
(F) Postmortem microscopic examination of the brain in some forms of reading disability demonstrates alterations in brain cell organization perhaps causal to the learning disability; and
(G) Some characteristics of learning disabilities may be favorably influenced by medication presumed to modify brain chemistry.
A useful model of the relationship between the brain and behavior recently has been elaborated for dyslexia (the learning disability affecting reading and writing). Research in the past 5 years suggests a physical means by which the dyslexic's behavior may be produced. The hypothesis as to how this phenomenon may occur with dyslexia may provide an explanation for the other variabilities in human aptitude not otherwise explained by genetic mechanisms.
Consistent anatomic findings have been observed in five consecutive postmortem CNS examinations of deceased dyslexies (four male and one female).16 The morphologic findings have included: 1) cell rests at the cortical surface referred to as ectopias; 2) infoldings of the surface of the brain referred to as polymicrogyria; and 3) disruption of the usual nerve cell organization of the cortex known as dysplasias. These morphologic alterations are primarily observed in the left hemisphere around the Sylvian fissure. This is the site for language localization in the adult as well as in the fullterm infant. Additionally, gross anatomic findings have suggested equal surface area of the left and right superior temporal lobes. Such symmetry is at odds from the usual pattern in autopsied human brains where 65% of any sample will reveal a definite leftgreater- than-right temporal lobe asymmetry. This pattern is observed as early as 33 weeks of gestation. Equality of right and left temporal surface area is observed in 25%. Ten percent demonstrate so-called reversed asymmetry in which the right is larger than the left temporal plane. n'14 Similar findings in all five cases support the hypothesis that the microscopic changes and the pattern of symmetry are correlated with dyslexic behavior.15'16 These alterations must occur during fetal brain development and have been postulated to take place between the 18th and 24th week of gestation.10
Norman Geschwind, the late James Jackson Putnam, Professor of Neurology at the Harvard Medical School, and his associate Albert Galaburda speculated that the male hormone testosterone might have interfered with the usual pattern of nerve cell migration.10 The favored left lateralization for the microscopic changes, he suggested, related to the fact that the right hemisphere completes its development more rapidly than the left. This would induce more change on the left where nerve cell migration time is greater. At the same time, enhanced right hemispheric development occurs explaining the increased rate of right-equal-toleft temporal surface area. The hypothesis suggests that unique visual spatial skills observed in many dyslexies, as well as in many left-handers, is the direct result of this altered pattern of brain development. This theory then explains the male preponderance, and higher frequency of left-handedness in the dyslexic population. With the involvement of the left hemisphere, the common association between dyslexia and a delay in spoken language development may then be explained. Geschwind suggested that these alterations should be considered the "pathology of superiority."17
If the notion of Geschwind and Galaburda10 is correct, a means then has been suggested by which variability in aptitude may be introduced at the time of human embryonic brain development which is beyond direct genetic control. That is, intrauterine environmental factors such as hormonal levels may affect the rate and the quality of nerve cell migration and their consequent connections as well as intra- and interhemispheric connections. This view arms physicians with a novel approach, as to the biological basis of human diversity. This view should caution educators that all students are not apt to leam alike, and that a biologic expectancy is that some students may be very good in one subject and rather poor in another.18
The articles that follow in this issue of Pediatrie Annals hopefully provide useful clinical insights. Bashir, Abrams, and Wiig address the group of learning disorders in which the hallmark is a deficit in expressive or receptive spoken language. Languagedeficient students suffer from the inability to communicate readily with those in their educational and emotional environment, placing them at risk for deficits in educational and social growth. Johnson reviews the plight of those students whose language is serviceable but whose deficit is in the non-word environment characterized by dysfunction of the right hemisphere. These students read and write reasonably well but are socially inappropriate and cannot interpret emotional messages in the faces, gestures, and vocal tones of those around them. Such students exhibit deficits in reading comprehension, some forms of mathematics such as geometry, and are poorly organized in their personal and academic lives. Gamett and Fleischner discuss those students whose presenting educational difficulty is in calculation and mathematic reasoning. The inability to quantify their environment places these students at risk greater than simply in failing mathematics. They do not "measure" themselves or others well either. Successful rehabilitation requires more than the provision of a hand-held calculator. Levine reviews the problems of disorders of attention where the unfocused concentration of the learner is not only disruptive to educability but to the social interactions of the student in school and at home. Woe to the student encumbered by ADD and one of the other learning disorders. Such multiply handicapped students need the sensitive support and judicious counsel of the well-trained physician. Proper medical care may enable educational therapy to succeed.
Whether the recently described histologie changes in the dyslexic population are confirmed as consistent and causal, or whether related changes are found to underlie other learning disabilities, remains to be seen. As medically based research carries important implications for education, this research only reinforces the historic tradition for physicians to assist in the identification and remediation of non-retarded students motivated to succeed but who struggle for mastery of basic academic subject matter.
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3. Orion ST: Specific reading disability- St rephosymbolia. JAMA 1928; 90:1095-1099.
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DSM-III Classification of Developmental Disorders