Alexia

DEFINITION

• Alexia is an acquired deficit in the ability to interpret written language; does not refer to those impairments (congenital or acquired early in life) which prevent the normal acquisition of reading skills (which are considered developmental dyslexia or simply dyslexia)

HISTORY

• Recognized for centuries, but became a significant problem only in 20th century, when literacy expectations increased considerably
• Origin of current concept of alexia stems from two case reports by Dejerine (1891, 1892); cases represent what has become known as central alexia and posterior alexia
• Dejerine’s alexia classification fell out of use until repopularized by Geschwind (1962)

MAJOR SYNDROMES (3 types)

Central Alexia (Alexia with Agraphia)

• Basic clinical features:
  • severe (not necessarily total) disturbance of both reading and writing
  • preserved ability to copy written language, but in slavish and non-comprehended manner
  • loss of ability to name letters, to comprehend spelled words, or to read out loud
• Often accompanied by other neurobehavioral disorders including:
  • aphasia
  • components of Gerstmann Syndrome (finger agnosia, right-left confusion, acalculia, and agraphia)
  • some degree of hemisensory loss and/or right homonymous visual field defict
• Locus of pathology includes inferior parietal lobe of language dominant hemisphere, centering on angular gyrus; typically damage to both cortex and white matter
• Causes most often from occlusion of MCA or distal branches (inferior parietal lobe); may also be caused by neoplastic lesions
• Other common names: semantic alexia, parieto-temporal alexia, total (literal and verbal) alexia, letter and word blindness, surface alexia

Posterior Alexia (Alexia without Agraphia)

• Basic clinical features:
  • Individual can comprehend written material
  • Writing is almost or totally w/in normal limits BUT can’t comprehend what write
  • Easily write but have more trouble copying written language
• With practice, can learn to read most letters out loud; words can then be spelled out loud and recognized auditorially
• In most cases, ass’d neuro findings include:
  • right homonymous hemianopia
  • color naming disturbance
• Pathology is typically infarction of left posterior artery territory, including splenium of CC (spares angular gyrus)
• Disconnects visual info from language cortex
• Other common names: verbal alexia, visual alexia, pure alexia, occipital alexia, associative alexia

Anterior Alexia (Frontal Alexia)

• More recently discovered so also known as the “Third Alexia”
• Basic clinical features:
  • Great difficulty naming individual letters of alphabet but can recognize some written words
  • Severe agraphia; ability to copy written language poor
  • Comprehend some spelled words, but poor at spelling aloud
  • Recognize some semantically meaningful words but fail to comprehend the grammatically significant function words – Agrammatism of written language
• Accompanying neuro findings:
  • Right hemiplegia
  • Nonfluent aphasia
  • May include unitlateral sensory and/or visual-field neglect
• Pathology is typically left frontal area
• Other common names: literal alexia, letter blindness

Table Summary of Three Major Syndromes

	POSTERIOR	CENTRAL	ANTERIOR
Written Language
Reading	Verbal alexia	Total alexia	Literal alexia
Writing to dictation	No agraphia	Severe agraphia	Severe Agraphia
Copying	Slavish	Slavish	Poor, clumsy, omissions
Letter naming	Relatively ok	Severe letter anomia	Severe letter anomia
Comp. of spelled words	Good	Failed	Some success
Spelling aloud	Good	Failed	Poor
Associated Findings
Language output	Normal	Fluent aphasia	Nonfluent aphasia
Motor	No paresis	Mild paresis	Hemiplegia
Motor apraxia	None	Sometimes	Frequently present
Sensation	No problems	Often sensory loss	Mild sensory loss
Visual Fields	Right hemianopia	Sometimes hemianopia	Usually ok
Gerstmann syndrome	Absent	Frequent	Absent

TERMINOLOGICAL CLARIFICATION

Note that lots of other subtypes of acquired reading disorders have been suggested

THREE LINGUISTIC SUBTYPES: subtypes based on categorization of modern linguistics

Phonological alexia (dyslexia)

• an inability to make spelling-to-sound correspondence rules
• results in visual paralexias; real words misread as visually similar words (“cat” for “car”)
• better reading of high frequency words
• spelling usually impaired

Surface alexia (dyslexia)

• grapheme-to-phoneme conversion disorder
• can’t read words with irregular orthography (e.g., “tough” read as “tug”)
• can read words with regular orthography

Deep alexia (dyslexia)

• prime feature of this disorder are reading errors based on semantic (real word) substitutions for target words (semantic paralexia)
• substituted word may be a semantic paralexia, a totally incorrect word, or neologism (“infant” could be read as “baby” “basement” or “garvon”)
• Syntactic (functional) words are almost totally omitted
• Pseudo words can’t be produced

OTHER ALEXIA TERMS

Global Alexia

• term used to indicate total loss of the ability to understand written or printed language
• synonymous with central alexia but indicates a total loss

Hemi-Alexia

• individual can read adequately in one visual field but not in other
• often seen when posterior CC is severed but both visual sensory areas remain intact

Hemi-Spatial Alexia

• denotes a reading d/o where only half of word is read
• seen in context of either a homonymous visual field or unilateral attention deficit (e.g., “basketball” read as “ball”)

Literal Alexia

• inability to recognize letters of alphabet
• significant feature of Anterior Alexia
• often contrasted with verbal alexia

Verbal Alexia

• opposite of Literal Alexia
• can read individual letters but can’t read full word
• seen in context of Posterior Alexia syndrome

Paralexia

• substitutions made when reading aloud
• multiple types: literal, semantic, phonemic, etc.

Spatial alexia

• disorder of reading based on difficulty perceiving location (place holding) of letters or words or maintaining the correct sequence of lines of print
• generally seen in context of right hemisphere dysfunction

Attentional dyslexia

• reading disorder characterized by gross disturbance in reading multiple words or text, secondary to disturbance in visual attention; single-word reading relatively preserved

Central dyslexias

• contrasted w/ peripheral dyslexias (below)
• disorder that affects processes by which word forms activate meaning or speech production mechanisms (“higher” language processes)
• Includes deep, phonologic, and surface dyslexias

Peripheral dyslexias

• term suggested by Shallice and Warrington (1980), contrasted w/ ‘central dyslexias’
• disorder caused by visual processing deficits in which visual inputs can’t be ass’d w/ stored representations of written words, includes attentional and neglect dyslexias and alexia without agraphia