Complete loss of speech output is more likely to be due to anarthria, that is, a motor disorder of articulation not limited to language. This convention is followed in this article and aphasia has been adopted for consistency. However, this situation is so uncommon in practice that the terms aphasia and dysphasia have come to be used interchangeably. The term aphasia, interpreted literally, should mean complete absence of language function. Writing is intact because left hemisphere language centres remain intact. It was conceptualised as a form of disconnection syndrome with a lesion of left primary visual cortex accompanied by a lesion to the splenium of the corpus callosum, cutting off visual input to the angular gyrus and thereby abolishing reading. This is a syndrome characterised by the inability to read with preserved writing. This view is outdated and often creates misunderstanding. Finally, the approach to the language system in medical textbooks remains dominated by Wernicke–Lichtheim’s 1874 model of the language system and the notion of canonical aphasia syndromes. Different disciplines have different traditions and approaches to the analysis of language disorders, which further reduces consistency of terminology.
There are various schemes to classify language disorders, which create overlapping terminology (eg, the expressive/receptive and fluent/dysfluent divisions of aphasia, see glossary in box 1). The presentations are varied and there are known pitfalls, such as the mislabelling of fluent aphasia as ‘confusion’. 4 The presence of aphasia also creates difficulties in case history taking, assessment and discussion about treatment options and decisions.ĭespite being common, language disorders are not always straightforward to evaluate in the clinic or at the bedside. 2 3 Disorders of language are disabling and cause distress to patients, carers and relatives. 1 Disorders of this system are common in everyday neurological practice, typically arising from focal injury to the left hemisphere and also from forms of selective neuronal degeneration. The flexibility and vast range of possible combinations in human language exceeds the scope of any other system for vocal communication between primates. Language is pivotal to everyday life and to human culture.
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