Transcortical Sensory Aphasia
The clinical presentation of poor comprehension with fluent but paraphasic speech and intact repetition is characteristic of transcortical sensory aphasia.
Key Distinguishing Features
The preservation of repetition is the critical diagnostic feature that differentiates this syndrome from other fluent aphasias 1. This pattern reflects:
- Fluent, paraphasic speech output - similar to Wernicke's aphasia, with word substitutions and neologisms 2
- Severely impaired comprehension - affecting both auditory and reading comprehension 3
- Preserved repetition ability - the pathognomonic feature that distinguishes it from Wernicke's aphasia 1
Anatomical Basis
The intact repetition occurs because the perisylvian language arc (connecting Wernicke's area, arcuate fasciculus, and Broca's area) remains structurally preserved 1. The lesion typically involves:
- Watershed zones in the posterior temporal-parietal regions
- Areas surrounding but sparing the core Wernicke's area 4
- Anterior temporal regions that are critical for semantic processing 4
Differential Diagnosis Algorithm
Wernicke's aphasia can be excluded because repetition is impaired in that syndrome due to direct damage to the Wernicke area and arcuate fasciculus 1, 4. Studies demonstrate that impaired repetition correlates with structural damage to the arcuate fasciculus and posterior temporal-parietal regions 1.
Conduction aphasia presents with impaired repetition as its hallmark feature (often due to auditory-verbal working memory deficits), making it incompatible with this presentation 1.
Global aphasia involves impairment across all language domains including repetition, comprehension, and expression 1.
Transcortical motor aphasia features non-fluent speech with preserved comprehension and repetition - the opposite pattern of what is described 1.
Clinical Pitfalls
A common error is confusing transcortical sensory aphasia with Wernicke's aphasia, as both present with fluent paraphasic speech and poor comprehension 2, 3. Always test repetition systematically - this single feature definitively separates these two syndromes 1.
The preservation of repetition despite severe comprehension deficits demonstrates that the Wernicke area itself is not sufficient for word comprehension when anterior temporal regions are damaged 4. This explains why patients can repeat what they hear without understanding it.