Learning Disorders

Michael P. Kerr

Mary Lou Smith

Introduction

The potential impact of epilepsy and its treatment on learning provides a considerable challenge for clinicians, patients, and families alike. In addition, the picture is often complicated by the association between the presence of epilepsy and apparently already coexistent disorders of learning and development. This poses important heuristic questions into the relative impact of epilepsy on the development of learning disorders.

It is beyond the scope of this chapter to address in detail this crucial question in the field of epileptology. For further reading please refer to the chapters on neonatal syndromes and syndromes of childhood and adolescence. This chapter will have as its focus the nature, impact, and management of epilepsy in those with an apparently coexistent intellectual disability (mental retardation). Such an approach helps the clarity of the chapter, yet it is important to reflect on how the populations of people who have intellectual disability are placed within the scope of learning disorders associated with epilepsy. This will be covered initially within our discussion on classification and terminology and later in the chapter within the section on the impact of epilepsy on people with an intellectual disability.

Key themes discussed in the chapter will include the association between certain syndromes of intellectual disability and seizure types, the impact of epilepsy, approaches to management, the association between epilepsy and behavioral disorders, and the multidisciplinary approach to care.

Classification and Terminology of Intellectual Disability

Considerable variation occurs in the terminology of intellectual disability. While intellectual disability is currently the internationally accepted term, mental retardation is favored in the United States and much of Europe, learning disability in the United Kingdom, mental handicap in much of the world during the 1990s, and intellectual handicap in Australia and New Zealand.

Definition of Disability

The American Association for Mental Retardation defines mental retardation as follows:

“Mental retardation is a disability characterized by significant limitations both in intellectual functioning and in adaptive behavior as expressed in conceptual, social and practical adaptive skills…. The disability originates before the age of 18.”

It adds five assumptions, which are essential to the application of the definition:

Limitations in present functioning must be considered within the context of community environments typical of the individual’s age, peers, and culture.
Valid assessment considers cultural and linguistic diversity as well as differences in communication, sensory, motor, and behavioral factors.
Within an individual, limitations often coexist with strengths.
An important purpose of describing limitations is to develop a profile of needed supports.
With appropriate personalized supports over a sustained period, the life functioning of the person with mental retardation generally will improve.

From a clinical viewpoint, particularly in administrative terms, mental retardation is defined using the International Classification of Diseases rubric, currently in its 10th version. All codes for mental retardation are prefixed with F7. Assessment should include clinical findings, adaptive behavior, and the use of psychometric tests.

The range of disability is defined in Table 1.

The Nature and Impact of Epilepsy in People with Intellectual Disability

Epidemiology

Epidemiologic data for this population are particularly influenced by methodologic and sampling issues, raising concerns regarding the interpretation of results that vary significantly depending on the study’s design.⁴¹^,⁹¹ These concerns focus on the usually selective nature of the population samples and difficulties in allowing for comparative levels of intellectual disability. The prevalence of epilepsy is significantly greater in people with intellectual disability than in the general population,⁶² with estimates in intellectual disability populations ranging from 18% to over 60%.

The major influences on prevalence estimates are (a) age; (b) residence, institution, or community; and (c) the severity of disability.¹⁸^,⁵⁷^,⁸⁴

Table 1 Classification of Intellectual Disability (ICD-10)

Code	Definition	Attributes
F70	Mild mental retardation	1) Ability to use speech 2) Full independence in self-care 3) IQ range between 50 and 69
F71	Moderate mental retardation	1) Slow in comprehension 2) Immobility or restricted mobility 3) Retarded motor skills 4) IQ range between 35 and 49
F72	Severe mental retardation	1) Marked impairment of motor skills 2) Clinically significant damage to CNS 3) IQ range between 20 and 34
F73	Profound mental retardation	1) Severely limited understanding 2) Immobility or restricted mobility 3) Incontinence 4) Requiring constant supervision 5) IQ <20 6) Usually organic etiology
CNS, central nervous system; ICD, International Classification of Diseases.

Table 2 Epidemiologic Surveys of the Prevalence of Epilepsy in People with Intellectual Disability (ID)

Sample	Prevalence
Children under age 14
Community SMR¹⁹	20%
Children up to 22 yr Community⁸⁵	Mild ID 24% Severe ID 44%
Institution⁶⁷	All 32%
Children 6–13 yr Community⁹⁷	Mild ID 14% Severe ID 24%
Adults, community based¹⁰⁸	All ID 22.1%
Community identified pediatric sample¹	All ID: 19% by age 10 years and 21% by age 22 years Severe ID: Fivefold risk as compared with mild ID
All ages, record-linked health data⁷¹	All ID 18.3%
Primary care health facilities⁶⁸	Down syndrome 13.6% Cerebral palsy 40%

Cohort effects, due to year of birth, are important in defining prevalence in both intellectual disability³⁷ and epilepsy.¹⁶

A comparison between community and institutionally based surveys⁶⁷^,¹⁰⁸ show as much as a 10% discrepancy in the prevalence found. Table 2 describes a range of epidemiologic surveys of the prevalence of epilepsy in people with intellectual disability.

The increasing prevalence of epilepsy with increasing severity of intellectual disability is well recognized in both children¹ and adults.⁴

Definition of seizure type in populations of people with intellectual disability has proven difficult.²⁴^,⁵⁷ An example of this is seen in a community study of children with intellectual disability.⁹⁰ In this survey, there was evidence of a lack of investigation in the population, with only 10% having had electrophysiologic tests. Despite this, they showed an increase in generalized tonic–clonic and myoclonic seizures and a decrease in partial seizures with increasing handicap. The authors concluded that this increase in generalized seizure disorder was an artifact of the lack of investigation, though other explanations such as genetic causes may be valid.

A Japanese study focusing on people with severe intellectual disability⁴ identified cerebral palsy as the most common etiology (42.3%); multiple seizure types were common (almost half had two or more seizures) and paroxysms were found on the electroencephalogram (EEG) in 90.6% of cases and abnormal computed tomography (CT) scan in 82.7% of cases. In a Finnish study in children,¹ prenatal causation was most frequent (47%), and seizures were most frequently partial (72%). As we shall see later, it is unrealistic when considering seizure type to take the intellectual disability population as a whole; individual etiologic characteristics are crucial in syndromal and seizure classification.

Etiologic Issues

Intellectual disability is caused by a range of pathologic processes, as, of course, is epilepsy. In particular, genetic advances into the individual causes of intellectual disability and of the epilepsies have expanded.⁵^,²¹

It is beyond the scope of this chapter to highlight all the etiologic processes involved in the development of an intellectual disability. Two issues are, however, of particular relevance to this population: (a) are specific etiologies associated with recognizable epilepsy patterns? and (b) what impact do seizures have on development and learning?

Etiology Associated Patterns of Epilepsy

A further approach to investigating the etiology of epilepsy in people with intellectual disability has been to define the nature of the epilepsy in individual disability syndromes. This approach will hopefully lead to the matching of known genetic abnormalities with the individual’s epilepsy and thus direct treatment options.

This section includes a brief overview of a select group of syndromes that have intellectual disability as a key feature, and that may also have epilepsy as a concomitant disorder. This section is not intended to provide a detailed analysis of the causes of the syndromes, or the etiology, features, or treatment of the associated epilepsies; these issues are reviewed in depth elsewhere in this textbook. This co-occurrence of epilepsy with these syndromes is important to recognize at a clinical level because the seizures add an additional burden to both the individual with the syndrome and to the caregivers.

Down Syndrome

Down syndrome (DS), or trisomy 21, is the most common genetic cause of intellectual disability.⁹³ In addition to intellectual disability, of which there is a range in severity, DS is characterized by growth retardation, hypotonia, a number of facial dysmorphologies, hypogonadism, an increased risk of cardiac disease and leukemia, and Alzheimer disease in those over the age of 35 years. A bimodal distribution in age of seizure onset has been described, with peaks in childhood and middle age.⁸²^,⁹⁸^,¹⁰⁵ The incidence of epilepsy increases with age, and the increase later in life is thought to be related to the onset and progression of Alzheimer disease.⁵⁴^,⁶³^,¹⁰⁵ A variety of seizure types have been reported, including infantile spasms, generalized tonic–clonic seizures, Lennox-Gastaut syndrome, and psychomotor seizures.⁴⁴^,⁸¹^,⁹⁸

Angelman Syndrome

Angelman syndrome (AS) is a genetic disorder that is estimated to account for up to 6% of all children presenting with severe intellectual disability and epilepsy.⁴² Clinical findings present in all patients include developmental delay, which becomes apparent by 6 to 12 months of age; severely impaired expressive language; ataxic (“puppetlike”) gait; tremulousness of limbs; and a typical behavioral profile, including a happy demeanor, hypermotor behavior, and low attention span. Although development may appear almost normal or only slightly delayed during the first 6 months of life, all patients eventually develop severe intellectual disability. The typical lack of speech may not be due to the intellectual disability alone; oral motor dyspraxia and deficits in social interaction and attention also contribute to the lack of expressive language.⁸⁰ Sleep problems may affect a significant portion of individuals with AS and are persistent; parents report adverse effects of their child’s sleep problems on their own well-being.²⁶^,⁹²

Seizures, abnormal electroencephalography, microcephaly, and scoliosis are observed in >80% of patients, with onset of epilepsy typically occurring in infancy or early childhood.³⁰^,³⁴ A variety of seizure types are seen, including febrile, atypical absence, generalized tonic-clonic, myoclonic, and clonic unilateral seizures.³⁹^,⁴³^,¹⁰⁶ There are contradictory data on whether the severity of the developmental disturbance in AS is related to the severity of epilepsy,⁵⁸^,⁷⁷ and whether there is an improvement in epilepsy with age.⁵⁹^,⁹²^,¹¹⁰

Fragile X Syndrome

Fragile X syndrome (FXS) is the most common known cause of autism or “autisticlike” behaviors, and the incidence of cognitive impairment is quite high. The clinical phenotype in the male typically also includes tall stature, large testes, relative macrocephaly, characteristic facial features, and delays in speech and language development.²³^,¹⁰⁰^,¹⁰⁹ Up to 80% of males with FXS are described as cognitively delayed. In the older studies of males with FXS, almost all were described as having moderate or severe mental retardation. However, many of these studies were based upon institutionalized males, and with better ascertainment studies, it has become clear that 10% to 15% of boys with FXS have a less severe degree of developmental delay, with IQs in the borderline or mild intellectual disability range. A high number of boys with fragile X (80% to 90%) are described as distractible and impulsive, with symptoms of attention deficit hyperactivity disorder, and anxiety is a common personality feature.³⁸

Girls with FXS tend to be less severely affected in terms of intellectual disability. Approximately 30% of girls with the full mutation have IQ scores above 85, with the other 70% mostly in the borderline or mild mental intellectual disability range.²³ However, those girls with normal intelligence are at higher risk for specific learning disabilities. The behavioral features in girls include shyness and poor eye contact.¹⁰⁰

Seizures occur in approximately 15% to 20% of children with FXS.⁶^,⁵³ Seizure types include absence, partial motor, generalized, and partial complex seizures; benign rolandic epilepsy is found frequently.⁶^,⁷³^,⁷⁴ Epilepsy in individuals with FXS generally follows a benign course, and in a relatively high number, seizures remit before the age of 20.⁸⁶

Rett Syndrome

In Rett syndrome (RS), there typically is normal development until 6 to 18 months (although as long as 30 months), after which development slows, or even deteriorates. The physical characteristics of RS include scoliosis, gait dyspraxia, and repetitive movements of the hands, often involving hand wringing. Individuals may have autonomic dysfunction, difficulty chewing, and teeth grinding, and eventually show growth failure and deceleration of head growth.⁴⁰^,⁴⁵ There is a high prevalence of behavioral and emotional disorders in RS, with anxiety, flat mood, self-injurious behavior, and autism seen frequently.⁴⁵^,⁸⁸ Frequently, there is a regression in cognition, behavior, and social and motor skills throughout the lifetime of patients with RS. The degree of developmental delay is usually within the severely to profoundly intellectually disabled range, although there is a spectrum of severity ranging from severe neurologic compromise to only minor neurologic symptoms.⁵¹ There is a preserved speech variant, which shows the same course and stereotypic hand movements, but patients typically recover some hand use and speech; epilepsy is rare in this group.²²

Epilepsy is common, occurring in between 80% and 95% of cases.⁴⁵^,⁹⁶ The severity of epilepsy may decrease with increasing age.⁹⁶ A variety of seizure types are found in RS, including generalized tonic–clonic, absence, myoclonic jerk, atonic, and tonic seizures. The incidence of true clinical seizures may be overestimated because the autonomic dysfunction may be incorrectly identified as absence or complex partial seizures.

The Impact of Epilepsy on Development and Learning

It is generally accepted that the causal process of epilepsy follows a path from brain damage through to the development of epilepsy.⁵⁷ Cognitive decline, as seen in a few patients with epilepsy, is usually associated with repeated head injury or through anoxic episodes in periods of status epilepticus. Other deterioration may be linked to seizures impacting information processing.⁸

However, increasing knowledge on conditions such as infantile encephalopathy (infantile spasms, myoclonic epilepsy) and the treatments for these devastating conditions seem to imply that epileptic phenomena can be associated with the development of intellectual disability.²⁷ A recent survey in Atlanta on the epidemiology and outcome of infantile spasms suggests that, at age 10 years, 83% will have intellectual disability.¹⁰³ The same survey suggested that 12% of 10-year-old children with profound intellectual disability had a history of infantile spasms.

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