Conduction Aphasia
This patient has conduction aphasia, characterized by the pathognomonic combination of fluent speech, preserved comprehension (ability to follow three-step commands), and severely impaired repetition, along with naming difficulties.
Diagnostic Algorithm
The key to diagnosing aphasia subtypes is systematically evaluating three core features:
- Fluency: This patient has fluent speech 1
- Comprehension: Preserved (follows three-step commands) 1
- Repetition: Impaired (cannot repeat phrases) 1, 2
Why Conduction Aphasia
Conduction aphasia is defined by the triad of fluent speech, relatively intact comprehension, and disproportionately impaired repetition, with frequent phonemic paraphasias and naming difficulties. 2, 3
The anatomical basis involves damage to the left temporoparietal region, specifically the posterior planum temporale (area Spt), which serves as an interface for integrating sensory and motor representations of speech 2. This region is critical for phonological working memory, and its damage explains why repetition is selectively impaired while the perisylvian language arc remains functionally intact 2.
Excluding Other Aphasia Types
Wernicke aphasia is excluded because comprehension is severely impaired in Wernicke's, whereas this patient can follow three-step commands 1. Additionally, repetition is also impaired in Wernicke's due to direct damage to Wernicke's area 1.
Transcortical sensory aphasia is excluded because repetition is preserved (often echolalic) in that syndrome, which is its defining feature that distinguishes it from Wernicke's 1. This patient cannot repeat phrases.
Transcortical motor aphasia is excluded because it presents with non-fluent speech, not fluent speech 1. This patient has fluent output.
Broca aphasia is excluded because it features non-fluent, effortful, telegraphic speech with relatively preserved comprehension 4. This patient's speech is fluent.
Clinical Features Supporting Conduction Aphasia
Patients with conduction aphasia typically demonstrate 2, 3, 5:
- Frequent phonemic paraphasias (sound substitutions) during speech 2, 3
- Self-correction attempts (conduit d'approche) 3
- Naming difficulties despite intact semantic knowledge 2, 5
- Phonological short-term memory deficits 2, 6
- Otherwise grammatical and fluent speech output 2, 7
Common Pitfall
The critical error is confusing conduction aphasia with transcortical sensory aphasia. The distinguishing feature is repetition: conduction aphasia has impaired repetition (the hallmark deficit), while transcortical sensory aphasia has preserved or even enhanced repetition despite poor comprehension. 1, 2