Pure alexia

Pure alexia is one form of alexia which makes up "the peripheral dyslexia" group. Individuals who have pure alexia suffer from severe reading problems while other language-related skills such as naming, oral repetition, auditory comprehension or writing are typically intact.

Pure alexia is also known as: "Dejerine syndrome", (after Joseph Jules Dejerine, who described it in 1892, but it should not be confused with medial medullary syndrome which shares the same eponym), "alexia without agraphia", "letter-by-letter dyslexia", "spelling dyslexia", or "word-form dyslexia".

Classification
Pure alexia results from cerebral lesions in circumscribed brain regions and therefore belongs to the group of acquired reading disorders, alexia, as opposed to developmental dyslexia found in children who have difficulties in learning to read.

Causes
Pure alexia almost always involves an infarct to the left posterior cerebral artery (which perfuses the splenium of the corpus callosum and left visual cortex, among other things). The resulting deficit will be pure alexia - i.e., the patient can write but cannot read (even what they have just written). This is because the left visual cortex has been damaged, leaving only the right visual cortex (occipital lobe) able to process visual information, but it is unable to send this information to the language areas (Broca's area, Wernicke's area, etc.) in the left brain because of the damage to the splenium of the corpus callosum. The patient can still write because the pathways connecting the left-sided language areas to the motor areas are intact.