A. Definitions

1. "Unexpected reading difficulty among children and adults who otherwise possess the intellingence, motivation, and schooling considered necessary for accurate and fluid reading"
2. Persistent, chronic reading disability
   1. Reader hears and understands meaning of word
   2. But reader cannot easily decode word in written form
3. Deficiency within a specific component of language system, the phonologic module
4. Phonologic module responsible for processing sounds of speech

B. Epidemiology

1. Most common learning disability among children and adults
2. Affects 80% of individuals identified as learning disabled
3. Reading ability occurs along a continuum
4. Dyslexia represents the lower end of the continuum's tail
5. Between 5% and 17.5% of children are dyslexic, depending upon diagnostic approach
6. Prevalence among males and females is equal
7. Untreated dyslexia will prevent even very bright individuals from reaching full potential

C. Phonologic-Deficit Hypothesis

1. Language
   1. Hierarchical system of increasingly complex components
   2. Most elementary component is the phoneme - smallest discernible element of speech
2. Speech requires:
   1. Retrieval of a word's phonemes
   2. Assembly of phonemes
   3. Pronunciation of word
3. Reading requires:
   1. Segmentation of word into phonemes
   2. Reassembly
   3. Then recognition and comprehension
4. Dyslexia occurs when an individual has difficulty separating word into phonemes
   1. Unable to separate word into phonemes, he or she cannot decode and identify word
   2. If word cannot be decoded and identified, higher order linguistic skills cannot be applied
   3. These higher order skills include comprehension
   4. The problem of dyslexia is very specific to the phoneme level
   5. Dysfunction occurs at the point where phonemes are symbolically represented by letters
5. Dyslexic individuals may be of normal or high intelligence,
   1. Dyslexics are capable of performing at a normal level on reading comprehension tests if they are aural, not written
   2. Dyslexics may have extensive spoken vacabularies and demonstrate normal conversational skills

D. Risk Factors for Dyslexia

1. Dyslexia is familial and heritable
2. Between 23% and 65% of children of a dyslexic parent will have the disability
3. Similarly, 40% of a dyslexic's siblings will also be dyslexic
4. Linkage studies implicate loci on chromosomes 4 and 15 in reading disability

E. Neurobiologic Studies

1. Differences demonstrated between normal and dyslexic brains by several methods
2. Major differences in temporo-parieto-occipital region compared to normal readers
   1. Postmortem examination, electrophysiologic studies, brain morphometry
   2. Functional imaging of brain confirm other studies
   3. Some studies implicate differences in the striate and extrastriate cortex
3. Findings consistent with lesions found in centered on angular gyrus in acquired alexia

F. Diagnosis

1. Patient often presents during childhood
2. Parents and teachers report poor school performance
3. Reading ability must be evaluated with psychometric testing
4. Testing for Dyslexia
   1. Single word reading tests are more sensitive than those which present a word in context
   2. Reading comprehension tests may produce false negative results
   3. This is because patient is able to guess at word meaning from context
   4. Phonetic decoding ability and IQ should both be evaluated
   5. Use of both tests will allow detection of discrepancies between ability and achievement
5. IQ testing may also be useful for identifying patients who are very bright but fail to read at a level commensurate with their overall intelligence

G. Assessment at School Entry

1. Previously, dyslexia was not detected until a child had fallen behind peers in reading ability, around third grade
2. Recent progress in understanding how reading skills are acquired has made it possible to diagnose and treat dyslexia before a child fails
3. Signs of dyslexia include (in the absence of hearing problems):
   1. Difficulty playing rhyming word games
   2. Speech punctuated by hesitation and dysfluencies
   3. Confusing words that sound similar
4. Nonspecific signs include:
   1. Factitious illnesses to avoid school
   2. Apprehension or anxiety about school

H. Assessment of Older Children and Adults

1. Dyslexia does not go away
2. Most patients improve their reading accuracy but not speed
3. Automaticity of reading ability (speed) must be evaluated to detect dyslexia among young adults at the college or graduate level of study
4. Untimed word recognition tests may be inadequate for diagnosing dyslexia among young adults at the college or graduate school level
5. The Nelson-Denny Reading Test may be administered under timed and untimed conditions and is thought to be a good choice for evaluating adults
6. Signs of possible dyslexia among adults include:
   1. Speech punctuated by hesitation and dysfluencies
   2. Confusing words
   3. Spelling problems
   4. Trouble reading new words
7. Patients may also be unable to complete assignments or tests requiring reading within the amount of time that normal readers of comparable intellectual ability require

I. Management

1. Early on, emphasis is on acquiring skills necessary for reading
2. For children to read, they must learn that:
   1. Spoken words can be broken into smaller units of sound (phonemes) and
   2. Letters on a page represent those sounds, and
   3. Written words have the same number and sequence of sounds in the spoken word (phonic)
3. Dyslexic children have great difficulty making the connections between spoken sounds and written words
   1. Structured, repetitive drills involving phonics and phonemes can be helpful
   2. This allows separate time to try to master reading
   3. Must also be allowed to apply their skills to reading passages and stories aloud
   4. Such reading practice permits a dyslexic child to experience reading for meaning
   5. Allows child to decode words in context
4. Large scale trials in progress for early treatments for dyslexia will clarify best practices
5. After a dyslexic has learned to read and progresses through elementary school, his or her curriculum becomes more content focused and less skill-acquisition oriented
6. At this point, management should emphasize accomodating his or her ability
7. The clinician can recommend a range of accomodations, such as:
   1. Untimed tests
   2. Longer timeframes for reading assignments
   3. Tape recording classes
   4. Recorded books
   5. Access to prepared syllabi and class notes
   6. Alternatives to written multiple choice exams (reports, oral exams)
   7. Access to a separate, quiet room for taking tests
   8. Joining a study group or hiring a tutor so the student can discuss what's being learned

References

1. Shaywitz SE. 1998. NEJM. 338(5):307