Merck Manual

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Stephen Brian Sulkes

, MD, Golisano Children’s Hospital at Strong, University of Rochester School of Medicine and Dentistry

Reviewed/Revised Feb 2022 | Modified Sep 2022
Topic Resources

Dyslexia is a general term for primary reading disorder. Diagnosis is based on intellectual, educational, speech and language, medical, and psychologic evaluations. Treatment is primarily educational management, consisting of instruction in word recognition and component skills.

Dyslexia is a specific type of learning disorder Overview of Learning Disorders Learning disorders are conditions that cause a discrepancy between potential and actual levels of academic performance as predicted by the person’s intellectual abilities. Learning disorders... read more . Learning disorders involve problems in reading, mathematics, spelling, written expression or handwriting, and understanding or using verbal and nonverbal language ( ).

No definition of dyslexia is universally accepted; thus, incidence is undetermined. An estimated 15% of public school children receive special instruction for reading; about half of these children may have persistent reading difficulties. Dyslexia is identified more often in boys than girls, but sex is not a proven risk factor for developing dyslexia.

The inability to learn derivational rules of printed language is often considered part of dyslexia. Affected children may have difficulty determining root words or word stems and determining which letters in words follow others.

Reading problems other than dyslexia are usually caused by difficulties in language comprehension or low cognitive ability. Visual-perceptual problems and abnormal eye movements are not dyslexia. However, these problems can interfere further with word learning.

Etiology of Dyslexia

Aural, rather than visual, problems are now thought to be the predominant causes of reading disabilities. Phonologic processing problems cause deficits in discrimination, blending, memory, and analysis of sounds. Dyslexia may affect both production and understanding of written language, which is often restricted further by problems with auditory memory, speech production, and naming or word finding. Underlying weaknesses in verbal language are often present.

Pathophysiology of Dyslexia

Dyslexia tends to run in families. Children with a family history of reading or learning difficulties are at higher risk. Because changes have been identified in the brains of people with dyslexia, experts believe dyslexia results predominantly from cortical dysfunction stemming from congenital neurodevelopmental abnormalities. Lesions affecting the integration or interactions of specific brain functions are suspected. Most researchers concur that dyslexia is left hemisphere–related and linked to dysfunctions in brain areas responsible for language association (Wernicke motor speech area) and sound and speech production (Broca motor speech area) and in the interconnection of these areas via the fasciculus arcuatus. Dysfunctions or defects in the angular gyrus, the medial occipital area, and the right hemisphere cause word recognition problems. Research suggests some malleability of brain systems in response to training.

Areas of the brain

Areas of the brain

Symptoms and Signs of Dyslexia

Dyslexia may manifest as

  • Delayed language production

  • Speech articulation difficulties

  • Difficulties remembering the names of letters, numbers, and colors

  • Difficulties with word problems despite normal math computation skills

Children with phonologic processing problems often have difficulty blending sounds, rhyming words, identifying the positions of sounds in words, and segmenting words into pronounceable components. They may reverse the order of sounds in words. Delay or hesitation in choosing words, substituting words, or naming letters and pictures is often an early sign. Short-term auditory memory and auditory sequencing difficulties are common.

Fewer than 20% of children with dyslexia have difficulties with the visual demands of reading. However, some children confuse letters and words with similar configurations or have difficulty visually selecting or identifying letter patterns and clusters (sound–symbol association) in words. Reversals or visual confusions can occur, most often because of retention or retrieval difficulties that cause affected children to forget or confuse the names of letters and words that have similar structures; subsequently, d becomes b, m becomes w, h becomes n, was becomes saw, and on becomes no. However, such reversals are normal in children < 8 years of age.

Although dyslexia is a lifelong problem, many children develop functional reading skills. However, other children never reach adequate literacy.

Diagnosis of Dyslexia

  • Reading evaluation

  • Speech, language, and auditory evaluations

  • Psychologic evaluations

Most children with dyslexia are not identified until kindergarten or 1st grade, when they encounter symbolic learning. Children with a history of delayed language acquisition or use, who are not accelerating in word learning by the end of 1st grade, or who are not reading at the level expected for their verbal or intellectual abilities at any grade level should be evaluated. Often, the best diagnostic indicator is the child’s inability to respond to traditional or typical reading approaches during 1st grade, although wide variation in reading skills can still be seen at this level. Demonstration of phonologic processing problems is essential for diagnosis.

Children suspected of having dyslexia should undergo reading, speech and language, auditory, cognitive, and psychologic evaluations to identify their functional strengths and weaknesses and their preferred learning styles. Such evaluations can be requested of school staff by the child’s teacher or family based on the Individuals with Disabilities Education Act (IDEA), the primary US special education law. Evaluation findings then guide the most effective instructional approach.

Comprehensive reading evaluations test word recognition and analysis, fluency, reading or listening comprehension, and level of understanding of vocabulary and the reading process.

Speech, language, and auditory evaluations assess spoken language and deficits in processing phonemes (sound elements) of spoken language. Receptive and expressive language functions are also assessed. Cognitive abilities (eg, attention, memory, reasoning) are tested.

Psychologic evaluations address emotional concerns that can exacerbate a reading disability. A complete family history of mental disorders and emotional problems is obtained.

Physicians should ensure that children have normal vision and hearing, either through office-based screening or referral for formal audiologic or vision testing. Neurologic evaluations may help detect secondary features (eg, neurodevelopmental immaturity or minor neurologic abnormalities) and rule out other disorders (eg, seizures).

Treatment of Dyslexia

  • Educational interventions

Treatment of dyslexia consists of educational interventions, including direct and indirect instruction in word recognition and component skills.

Direct instruction includes teaching specific phonics skills separate from other reading instruction. Indirect instruction includes integrating phonics skills into reading programs. Instruction may teach reading from a whole-word or whole-language approach or by following a hierarchy of skills from the sound unit to the word to the sentence. Multisensory approaches that include whole-word learning and the integration of visual, auditory, and tactual procedures to teach sounds, words, and sentences are then recommended.

Component skills instruction consists of teaching children to blend sounds to form words, segment words into word parts, and identify the positions of sounds in words. Component skills for reading comprehension include identifying the main idea, answering questions, isolating facts and details, and reading inferentially. Many children benefit from using a computer to help isolate words within text samples or for word processing of written work.

Compensatory strategies, such as using audiobooks and taking notes using a digital recorder, can help children in later elementary school grades master content while continuing to build reading skills.

Other treatments (eg, optometric training, perceptual training, auditory integration training) and drug therapies are unproved and not recommended.

Key Points

  • Dyslexia involves difficulty reading, and producing and understanding written language; there may also be problems with auditory memory, speech production, naming or word finding, and word problems.

  • Dyslexia probably results from congenital neurodevelopmental abnormalities that affect left hemisphere brain areas responsible for language association, sound and speech production, the interconnections between these areas, or a combination.

  • Children may have delayed language production, but sometimes the first indicator is inability to respond to typical reading instruction during early elementary grades.

  • Rule out cognitive, psychologic, hearing, and vision disorders.

  • Various educational interventions are used, but research does not support optometric training, perceptual training, or auditory integration training for most children.

More Information

The following are English-language resources that may be useful. Please note that THE MANUAL is not responsible for the content of these resources.

NOTE: This is the Professional Version. CONSUMERS: View Consumer Version
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