Pure alexia

Pure alexia, also known as agnosic alexia or alexia without agraphia or pure word blindness, 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: "alexia without agraphia", "letter-by-letter dyslexia", "spelling dyslexia", or "word-form dyslexia". Another name for it is "Dejerine syndrome", after Joseph Jules Dejerine, who described it in 1892; however, when using this name, it should not be confused with medial medullary syndrome which shares the same eponym.

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.

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). However, because pure alexia affects visual input, not auditory input, patients with pure alexia can recognize words that are spelled out loud to them. 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. Patients with this deficit mostly do suffer from a stroke to the posterior cerebral artery. But they may be susceptible to pure alexia as a consequence of other traumatic brain injuries (TBIs) as well. Anything that stops proper blood flow to the area necessary for normal reading abilities will cause a form of alexia. The posterior cerebral artery is a main local for the cause of this deficit because this artery is not just responsible for itself. It also supplies the anterior temporal branches, the posterior temporal branches, the calcarrine branch, and the parieto-occipital branch. What is important about these arteries is their location. All of them supply blood to the back outer parts of the brain. This part of the brain is also referred to as the posterior lateral part of the brain. In cases of pure alexia, locations are found in the section of the brain, specifically the temporo-occipital area. This is the area that is activated when people without any sort of alexia receive activation when undergoing orthographic processing. This area is known as the visual word form area due to this pattern of activation.

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