What is the difference between dyslexia and alexia in terms of diagnosis, management, and treatment?

Dyslexia vs. Alexia: Key Distinctions

Dyslexia is a developmental disorder where children fail to acquire normal reading skills despite adequate education, while alexia is an acquired reading disorder caused by brain damage in previously literate adults—these are fundamentally different conditions requiring distinct diagnostic and management approaches. 1, 2

Core Definitions and Pathophysiology

Dyslexia (Developmental Reading Disorder)

• Dyslexia represents a neurodevelopmental disorder where the brain fails to develop normal reading capabilities during childhood, despite adequate intelligence and educational opportunities 2
• The condition reflects dysfunction in various cerebral areas, more frequently in the left hemisphere, affecting sequential information processing and language-related cortical development 2
• Genetic, chromosomal, and hormonal/immunological factors may disrupt cortical language area development (migration disorders and abnormal asymmetry), preventing normal left hemispheric dominance from establishing 2
• Multiple subtypes exist including dysphonemic (auditory-phonological), visual dyslexia, and subtypes related to speech production, semantics, and linguistic memory 2

Alexia (Acquired Reading Disorder)

• Alexia is an acquired loss of reading ability due to brain damage (most commonly stroke or tumor) in someone who was previously literate—this is fundamentally different from dyslexia's developmental failure 3, 1
• The condition must be distinguished from dyslexia (developmental) and illiteracy (lack of education) 3
• Alexia is classified into peripheral alexia (perceptual/attentional deficits) and central alexia (language-based deficits commonly seen with aphasia) 1

Diagnostic Approach

Diagnosing Dyslexia

• Diagnosis should begin at early age through assessment of reading acquisition difficulties in the context of normal intelligence and adequate educational exposure 2
• Evaluate for associated neuropsychological dysfunctions including phonological processing deficits, sequential information processing problems, and language production difficulties 2
• Neuroimaging may reveal cortical abnormalities in language areas, though this is not routinely required for diagnosis 2

Diagnosing Alexia

• Establish the timeline of onset—alexia presents acutely or subacutely following identifiable brain injury, distinguishing it from lifelong dyslexia 3, 1
• Neuroimaging (MRI) is crucial to identify specific lesion locations: left ventral occipitotemporal cortex for pure alexia, left angular gyrus for alexia with agraphia, or right hemisphere/bilateral lesions for attentional alexia 4, 1
• Assess whether agraphia (writing impairment) is present, as this helps localize the lesion and classify the syndrome 4, 3
• Test for associated deficits: aphasia, visual field defects (hemianopia), visuospatial dysfunction, or attentional problems 3, 1
• Perform linguistic analysis examining word-length effects, part of speech, word frequency, imageability, and ability to use grapheme-to-phoneme rules 5

Specific Alexia Syndromes

Pure Alexia (Alexia Without Agraphia)

• Patients can write but cannot read words or letters, representing a perceptual word-form agnosia 1, 5
• Associated with damage to left ventral occipitotemporal cortex or its connections 1
• Reading varies with word-length but not linguistic variables; preserved grapheme-to-phoneme pronunciation rules allow better reading of pseudo-words and regularly spelled words 5
• Letter discrimination is impaired 5

Alexia With Agraphia

• Localized primarily to the left angular gyrus in the dominant parietal lobe 4
• Represents a linguistic deep dyslexia with impaired access to internal lexicon and phoneme-to-grapheme rules 5
• Better letter and word recognition than pure alexia, but shows semantic errors and inability to use grapheme-to-phoneme rules 5
• Reading is better for high-imageability words 5
• Often associated with other language impairments as part of progressive aphasic syndrome or posterior cortical atrophy 4
• The American Academy of Neurology recommends considering Alzheimer's disease as the most common etiology, with frontotemporal lobar degeneration and Lewy body dementia as less common causes 4

Hemianopic Alexia

• Associated with less extensive occipital damage causing visual field defects 1
• Creates problems reading longer words and passages of text due to the hemianopia itself 1

Attentional Alexia

• Arises from attentional deficits, most commonly following right hemisphere or bilateral lesions 1

Management and Treatment

Dyslexia Management

• Treatment should begin at early age and be acknowledged as having great social importance 2
• Interventions focus on phonological awareness training, multisensory structured language education, and accommodations in educational settings 2
• No specific pharmacological treatment exists; management is educational and behavioral 2

Alexia Management

• Early recognition is important for appropriate rehabilitation planning 4
• Patients with alexia without agraphia may benefit from specific reading rehabilitation techniques, despite being initially thought unsuitable for rehabilitation 4
• For alexia associated with aphasia, treatment for aphasia should be offered as early as tolerated 6
• In the first four months after stroke, people with aphasia should be given opportunity to practice language and communication with a speech-language therapist as frequently as tolerated 6
• Intensive aphasia therapy (at least 45 minutes of direct language therapy for five days a week) may be used in the first few months after stroke 6
• Computerized treatment may be considered to supplement treatment provided by a speech-language pathologist 6
• Address underlying neurodegenerative disease if present (Alzheimer's disease, frontotemporal dementia) with comprehensive management 4

Critical Pitfalls to Avoid

• Do not confuse developmental dyslexia with acquired alexia—the former is present from childhood, the latter occurs after brain injury in previously literate individuals 3, 1, 2
• Do not assume absence of agraphia rules out significant alexia—writing can mirror reading deficits and may be subtle in some cases 5
• Do not overlook alexia in stroke patients—writing and reading disorders are more frequent than verified on routine examination 3
• Do not miss underlying neurodegenerative disease when alexia with agraphia presents, particularly Alzheimer's disease 4
• Do not delay rehabilitation based on outdated assumptions that certain alexia types are untreatable 4