Pure word deafness in a patient with early-onset Alzheimer's disease: an unusual presentation

Auditory phonological identification impairment in primary progressive aphasia

OBJECTIVE

To examine the audiological characteristics and neuroanatomical regions associated with auditory phonological identification impairment in primary progressive aphasia (PPA).

METHODS

Twenty-seven patients with PPA [13 non-fluent/agrammatic variant PPA (nfvPPA), three logopenic variant PPA (lvPPA), seven semantic variant PPA (svPPA), and four mixed type PPA] were included in the study. Neuropsychological, language, audiological, and neuroradiological examinations were also performed. Auditory function examinations consisted of a pure-tone threshold test, a phonological identification task, and temporal auditory acuity tests, such as click counting or fusion. As an evaluation value of phonological identification ability, we calculated the discrepancy scores, which were the smaller discrepancy (left or right ear) in phonological identification ability scores between measured and expected values from the pure-tone threshold. In the neuroradiological examination, we evaluated the regional cerebral blood flow using 123I-iodoamphetamine single-photon emission computed tomography.

RESULTS

Eight of the 27 patients were allocated to the impaired phonological identification group, and four were considered to have significant impairment on further analysis. Two of these patients, one with lvPPA and one with mixed type of lvPPA and nfvPPA, showed apparent phonological identification deficits that could be observed in daily life. The discrepancy scores were not significantly related to the results of neuropsychological, language, or any other auditory examinations, except for the click counting score in the left ear. Voxel-based correlation analyses revealed that regional cerebral blood flow in the bilateral superior temporal gyrus and bilateral primary auditory cortex was significantly and positively correlated with phonological identification ability.

CONCLUSIONS

Our results suggest that progressive dysfunction of the bilateral superior temporal gyrus and bilateral primary auditory cortex due to neurodegenerative diseases leads to phonological identification impairment in PPA syndrome.

The Auditory Agnosias: a Short Review of Neurofunctional Evidence

PURPOSE OF REVIEW

To investigate the neurofunctional correlates of pure auditory agnosia and its varieties (global, verbal, and nonverbal), based on 116 anatomoclinical reports published between 1893 and 2022, with emphasis on hemispheric lateralization, intrahemispheric lesion site, underlying cognitive impairments.

RECENT FINDINGS

Pure auditory agnosia is rare, and observations accumulate slowly. Recent patient reports and neuroimaging studies on neurotypical subjects offer insights into the putative mechanisms underlying auditory agnosia, while challenging traditional accounts. Global auditory agnosia frequently results from bilateral temporal damage. Verbal auditory agnosia strictly correlates with language-dominant hemisphere lesions. Damage involves the auditory pathways, but the critical lesion site is unclear. Both the auditory cortex and associative areas are reasonable candidates, but cases resulting from brainstem damage are on record. The hemispheric correlates of nonverbal auditory input disorders are less clear. They correlate with unilateral damage to either hemisphere, but evidence is scarce. Based on published cases, pure auditory agnosias are neurologically and functionally heterogeneous. Phenotypes are influenced by co-occurring cognitive impairments. Future studies should start from these facts and integrate patient data and studies in neurotypical individuals.

Case Report: Semantic Variant Primary Progressive Aphasia With Impaired Verbal Word Discrimination

Some patients with primary progressive aphasia (PPA) present with various types of hearing deficits. Research on the auditory function and speech sounds in PPA, including temporal, phonemic, and prosodic processing, revealed impairment in some of these auditory processes. Many patients with PPA who present with impaired word recognition subsequently developed non-fluent variant PPA. Herein, we present a patient with semantic variant PPA (svPPA) who demonstrated impaired verbal word discrimination. Audiological examinations revealed normal auditory brainstem responses and slightly impaired pure-tone perception. By contrast, verbal word discrimination and monosyllable identification were impaired, and temporal auditory acuity deteriorated. Analyses of brain magnetic resonance images revealed a significant decrease in the gray matter volume in bilateral superior temporal areas, predominantly on the left, compared with those of patients with typical svPPA, which appeared to be associated with impaired word recognition in our patient.

Cortical disorders of speech processing: Pure word deafness and auditory agnosia

Selective disorders of auditory speech processing due to brain lesions are reviewed. Over 120 years after the first anatomic report (Dejerine and Sérieux, 1898), fewer than 80 cumulative cases of generalized auditory agnosia and pure word deafness with documented brain lesions are on record. Most patients (approximately 70%) had vascular lesions. Damage is very frequently bilateral in generalized auditory agnosia, and more frequently unilateral in pure word deafness. In unilateral cases, anatomical disconnection is not a prerequisite, and disorders may be due to functional disconnection. Regardless of whether lesions are unilateral or bilateral, speech processing difficulties emerge in the presence of damage to the superior temporal regions of the language-dominant hemisphere, suggesting that speech input is processed asymmetrically at early stages already. Extant evidence does not allow establishing whether processing asymmetry originates in the primary auditory cortex or in higher associative cortices, nor whether auditory processing in the brainstem is entirely symmetric. Results are consistent with the view that the difficulty in processing auditory input characterized by quick spectral and/or temporal changes is one of the critical dimensions of the disorder. Forthcoming studies should focus on detailed audiologic, neurolinguistic, and neuroanatomic descriptions of each case.

Pure word deafness due to bilateral temporal lobe ischemic stroke occurring at different time points over the years: a case report on the insight of brain language network reorganization

Here we present a case of a native Greek male patient who presented clinically with sudden onset pure word deafness after an ischemic stroke in the temporoparietal region of the right hemisphere, but who had suffered an ischemic stroke 9 years previously in an adjacent area of the left hemisphere, causing aphasic symptoms which resolved quickly and almost completely. What makes this case interesting and novel is that it is the first case describing a patient whose ventral language comprehension circuit did not reorganize successfully due to damage of the adjacent right hemisphere language areas at a subsequent time.

Preferential Disruption of Auditory Word Representations in Primary Progressive Aphasia With the Neuropathology of FTLD-TDP Type A

Four patients with primary progressive aphasia displayed a greater deficit in understanding words they heard than words they read, and a further deficiency in naming objects orally rather than in writing. All four had frontotemporal lobar degeneration-transactive response DNA binding protein Type A neuropathology, three determined postmortem and one surmised on the basis of granulin gene (GRN) mutation. These features of language impairment are not characteristic of any currently recognized primary progressive aphasia variant. They can be operationalized as manifestations of dysfunction centered on a putative auditory word-form area located in the superior temporal gyrus of the left hemisphere. The small size of our sample makes the conclusions related to underlying pathology and auditory word-form area dysfunction tentative. Nonetheless, a deeper assessment of such patients may clarify the nature of pathways that link modality-specific word-form information to the associations that mediate their recognition as concepts. From a practical point of view, the identification of these features in patients with primary progressive aphasia should help in the design of therapeutic interventions where written communication modalities are promoted to circumvent some of the oral communication deficits.

Wernicke's area revisited: parallel streams and word processing

Auditory word-form recognition was originally proposed by Wernicke to occur within left superior temporal gyrus (STG), later further specified to be in posterior STG. To account for clinical observations (specifically paraphasia), Wernicke proposed his sensory speech center was also essential for correcting output from frontal speech-motor regions. Recent work, in contrast, has established a role for anterior STG, part of the auditory ventral stream, in the recognition of species-specific vocalizations in nonhuman primates and word-form recognition in humans. Recent work also suggests monitoring self-produced speech and motor control are associated with posterior STG, part of the auditory dorsal stream. Working without quantitative methods or evidence of sensory cortex' hierarchical organization, Wernicke co-localized functions that today appear dissociable. "Wernicke's area" thus may be better construed as two cortical modules, an auditory word-form area (AWFA) in the auditory ventral stream and an "inner speech area" in the auditory dorsal stream.