Slowly Progressive Alexia
SIR: Semantic dementia is a progressive neurodegenerative disorder usually characterized by relatively isolated fluent aphasia.1 The underlying cognitive disorder is an impairment in semantic knowledge for language.1 A patient with progressive reading difficulty as the initial and predominant manifestation of semantic dementia is reported below.
Case Report
>A 55-year-old right-handed, English-speaking man had a 2-year history of progressive reading difficulty. During the last year, the patient had also developed word-finding difficulty that was less severe than his reading difficulty. He had an otherwise negative medical history.
On examination, his verbal output was fluent with occasional word-finding pauses. He generated a word list of 11 animals in a minute and named 9 of 15 items on the mini-Boston Naming Test. He failed to pick the correct name when given a 4-word multiple choice task for each of the 6 missed pictures. At one point he said, “I don't know what to call it, I don't know the word anymore, I have to constantly work at understanding words.” Auditory comprehension, memory, visuospatial constructions, calculations, proverb interpretation, and results of elementary neurological examination were otherwise normal.
The patient was given a reading test. He was asked to read aloud 232 words containing 56 words with regular spelling, 56 words with irregular grapheme–phoneme correspondence (exception words), and 120 nonsense words.2 The patient correctly pronounced all of the regular and nonsense words but only 37 of the exception words (χ2=65.6, df=3, P<0.001). He made regularization errors. None of the 19 misread words was comprehended, even with category or phonemic cues, but they all invoked a sense of familiarity for the word. He could not spontaneously comprehend 6 of the exception words that he correctly read, although 4 of these responded to a category cue. On a subsequent naming task, he correctly generated 6 of the misread words.
Laboratory data were unremarkable except for a PET scan that showed decreased tracer uptake in both temporal lobes, left worse than right.
Comment
The patient's illness began with progressive reading difficulty consistent with the entity of surface dyslexia. He had difficulty reading irregular words but had preserved reading for regular words and nonsense words. Later in his course, he developed semantic anomia consistent with semantic dementia and his left temporal lobe pathology.
Semantic dementia and surface dyslexia frequently occur together. Various theories have proposed difficulties in the relationship between reading and semantics at the presemantic, semantic, or postsemantic levels.3–5 This patient's reading difficulty was not presemantic because he could read some irregular words without comprehension. It was not postsemantic because he consistently comprehended only words that were correctly read. In addition, the misread words seemed familiar, category clues facilitated their comprehension, and many of these words were verbally generated in a naming task.
In summary, a slowly progressive alexia, or surface dyslexia, was the initial manifestation of this patient's semantic dementia. On testing, irregular written words appeared to have disproportionate difficulty gaining access to semantic information.
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4 Patterson K, Hodges JR: Deterioration of word meaning: implications for reading. Neuropsychologia 1992; 30:1025-1040Crossref, Medline, Google Scholar
5 Watt S, Jokel R, Behrmann M: Surface dyslexia in nonfluent progressive aphasia. Brain Lang 1997; 56:211-233Crossref, Medline, Google Scholar
