Alexias and Agraphias

ALEXIA WITHOUT AGRAPHIA

Alexia without agraphia was first described by Dejerine in 1892 in a patient who suddenly lost the ability to read but had no other language disturbance. The only neurological finding of significance was a right homonymous hemianopia. Although the patient was unable to read except for some individual letters, he could write adequately. In patients with this syndrome, the patient can write but cannot read his or her own written output. If the letters of a word are read aloud, the patient can often put them together so that the word can be deciphered. The patient often has verbal alexia, which refers to an inability to read words (also called word blindness) but not literal alexia (letter blindness), retaining the ability to read letters. The patient with alexia without agraphia can recognize individual letters when they are drawn in the palm or palpated from embossed blocks. Patients with this syndrome do not lose the ability to see verbal stimuli, but visual information has lost access to the language area. Patients with this disorder also have greater difficulty in copying written material than in producing words to dictation. They can spell words out loud without difficulty. Many patients have disturbed color naming as well as a mild degree of anomia. Some have difficulty in reading numbers and others suffer from true acalculia.

The causative lesion is nearly always a stroke in the territory of the left posterior cerebral artery, with infarction of the medial occipital lobe, the medial temporal lobe, and the splenium of the corpus callosum. Dejerine suggested a disconnection between the intact right visual cortex and the left hemisphere areas mediating language, particularly the angular gyrus. Geschwind repopularized this disconnection theory. y

As a separate but closely related entity, Greenblatt y has described a syndrome that he named subangular alexia. Patients with this disorder have alexia without agraphia and without hemianopia. The structural pathology in these cases involves the white matter deep in the dominant parietal cortex, undercutting the angular gyrus.

ALEXIA WITH AGRAPHIA

In 1891, Dejerine also described a syndrome of alexia with agraphia in a patient who suffered a cerebral vascular accident. The ability to read both letters and words is impaired, and there is equal difficulty in comprehension of numbers and musical notation. Cues are of little help. Thus, tracing the letter with the finger does not aid in identification, and the patient with this type of alexia cannot decipher a word when it is spelled aloud for him. The writing disturbance is usually of equal severity. The ability to copy written material is far better than the ability to produce it on command. This syndrome may be considered an acquired illiteracy, in which a previously educated patient is rendered unable to read and write.

This disorder often overlaps with Wernicke's aphasia. In those cases, the patients often have a paraphasic output, impaired naming, and repetition, as well as disturbed written comprehension (word blindness) more than auditory comprehension (word deafness). Associated findings include right hemianopia or superior quadrantanopia, elements of Gerstmann's syndrome, and right-sided sensory loss. Most often, there is partial recovery, permitting only limited reading comprehension.

The most common locus of pathology in this syndrome is situated in the parietotemporal junction of the dominant hemisphere, particularly in the angular gyrus.

The association of alexia with agraphia in Gerstmann's syndrome and anomia has been called the angular gyrus syndrome, and the combined disorder almost invariably indicates a left hemisphere inferior parietal location of the causative pathology. y

FRONTAL ALEXIA

A number of features of frontal alexia are sufficiently distinctive to allow differentiation from the other varieties of alexia. y Most patients with the disorder can read, both aloud and for comprehension, but only isolated words from a given sentence are uttered; the recognized words are almost exclusively substantives. If relational words such as adjectives and prepositional phrases are the determining language structures, the patient may completely misinterpret the sentence. Nonfluent aphasia is often associated with frontal alexia. The site of pathology in frontal alexia involves the same locus as Broca's aphasia.

Other types of alexias have been described, including hemialexia following posterior corpus callosum section, unilateral paralexia, a manifestation of unilateral inattention, and other variants. y

AGRAPHIA

Agraphia may be defined as a loss or impairment of the ability to produce written language, caused by brain dysfunction. Almost without exception, every individual with aphasia shows at least some degree of agraphia, and tests of writing ability can be used as a screening device to detect the presence of aphasia. Caution is necessary, however, because agraphia accompanies many disturbances other than aphasia. y Abnormalities of constructional skills, visuospatial discrimination, and disturbances of motor skills, such as ataxia, rigidity, spasticity, chorea, myoclonus, and tremor, cause major alterations in the quality of graphic output.

Three variations of agraphia are outlined. y Left frontal (anterior) agraphia is seen in patients with Broca's aphasia, and their written output parallels their verbal output. Words and letters are large and messy with poor spelling, and sentences are devoid of grammatical words (agrammatism). Left parietotemporal (posterior) agraphia is seen in patients with posterior aphasias, and written output parallels their spoken output. Literal and verbal paragraphias as well as empty writing are present. Visuospatial agraphia is most commonly associated with posterior right hemisphere defects causing constructional disturbance. The script is well formed but there is a tendency for the written line to slant upward and for the left margin to be larger and increasing in size with subsequent lines.

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