Alexia without agraphia: a study of a case of verbal alexia without accompanying colour-naming defect
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Summary
A 47-year-old man developed a persistent form of alexia without agraphia as the result of a haemorrhagic intracerebral lesion in the left inferior temporo-occipital region, due to the rupture of an arteriovenous malformation. Surgical evacuation of the haematoma and excision of the malformation did not produce any modification of the reading deficit, which remained unchanged during a 4-year follow-up. The reading deficit was restricted to words and the patient was able to read only letter-by-letter, so that the whole words were reconstructed from the auditory names of the letters. So far, the disconnection explanation is the standard explanation of alexia without agraphia and the present case of verbal alexia may be regarded as being within this overall category. However, this explanation meets with unanswered questions that suggest more flexible interpretations. Neurolinguistic studies have questioned the unique character of alexia without agraphia as a clinical entity and, in contrast to the disconnection hypothesis, support the notion that the different varieties of alexia that are traditionally described represent distinctive syndromes, each with its own clinical features and pathophysiological basis. In this context, the reading properties in this case seem fully compatible with a deficit of the visual word-form system postulated by Warrington and Shallice, that is, the relatively early stage of the reading process through which a word-form or equivalent unit is attained. This system might be lateralized to the left hemisphere, as suggested by the fact that this case, like other cases of verbal alexia, had sustained damage to the left hemisphere and did not show any differential preservation of the reading of concrete words.
Key words
Alexia without agraphia Verbal alexia Letter-by-letter reading Disconnection Visual word-form systemZusammenfassung
Bei einem 47jährigen Mann trat eine intracerebrale Blutung infolge Ruptur eines arteriovenösen Angioms der linken basalen Temporookzipitalregion auf. Dies führte zu einer persistierenden Alexie ohne Agraphie. Auch die chirurgische Ausräumung des Hämatoms und der Mißbildung bewirkte keine Veränderung der Leseschwierigkeiten, die während vier Jahren konstant blieben. Die Lesestörung beschränkte sich auf Wörter, und der Patient war lediglich fähig, Buchstabe um Buchstabe zu lesen, so daß das Gesamtwort lediglich rekonstruiert wurde. Bisher beruht die Standarderklärung der Alexie ohne Agraphie auf der Diskonektionstheorie und der vorgelegte Fall verbaler Alexie kann innerhalb dieser Kategorie gedeutet werden. Immerhin wirft dieser Fall eine Reihe von offenen Fragen auf, welche eine flexiblere Interpretation nahelegen. Neurolinguistische Studien haben den einmaligen Charakter der Alexie ohne Agraphie als klinische Entität in Frage gestellt und sprechen — im Gegensatz zu der Diskonektionshypothese — zugunsten der Annahme, daß unterchiedliche Arten von Alexie auch eigenständige Syndrome darstellen, jedes davon mit seinen eigenen klinischen Eigenheiten und pathophysiologischen Grundlagen. In diesem Zusammenhang scheinen die Leseeigentümlichkeiten im vorliegenden Fall kompatibel zu sein mit einem Defizit des visuellen Wort-Formsystemes, wie es von Warrington und Shallice postuliert wurde: das ist ein relativ frühes Stadium des Leseprozesses durch welches eine Wortform oder äquivalente Einheit erreicht wird. Dieses System könnte im Bereiche der rechten Hemisphäre lokalisiert sein, wofür ein Argument im vorliegenden Fall, wie auch in anderen Fällen von verbaler Alexie sprechen würde: hier war eine Läsion der linken Hemisphäre erzeugt worden, ohne daß irgend eine selektive Erhaltung der Fähigkeit zum Lesen konkreter Worte nachweisbar gewesen wäre.
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