Continuing Education Activity

Conduction aphasia is a rare form of aphasia in which both expression and comprehension remain intact, but the patient shows an isolated impairment in their ability to repeat simple phrases. Carl Wernicke first proposed that a disconnection between the two speech systems, Broca area, and Wernicke area, leads to this unique condition. Ludwig Lichtheim and Norman Geschwind expanded on Wernicke's work, and this model became the common explanation for conduction aphasia. In this model, there is a lesion in the arcuate fasciculus which connects the two para-Sylvian speech centers. Recent studies have suggested that this is an incomplete model of conduction aphasia in that lesions outside of the arcuate fasciculus can also lead to the clinical presentation of this phenomenon. This activity examines when conduction aphasia should be considered on differential diagnosis and how to properly evaluate it and its underlying cause. This activity highlights the role of the interprofessional team in caring for patients with this condition.

Objectives:

• Describe the lesions that result in conduction aphasia.
• Identify how conduction aphasia differs from Wernicke and Broca aphasia.
• Review the role of neuroimaging in determining the etiology of conduction aphasia.
• Explain the importance of interprofessional collaboration among members of the clinical team to remediate the effects of the conduction aphasia.

Introduction

Aphasia is a term to describe a disturbance of language function that results from brain injury. Most commonly, clinicians characterize aphasia as either a Broca aphasia/expressive aphasia (with decreased verbal fluency) or a Wernicke aphasia/receptive aphasia (with decreased comprehension) depending on the location of the brain lesion.[1] Conduction aphasia is a rare form of aphasia where both expression and comprehension remain intact, but the patient shows an isolated impairment in the ability to repeat simple phrases.[2] Carl Wernicke first proposed that a disconnection between the two speech systems (Broca area and Wernicke area) leads to this unique condition.[3] Ludwig Lichtheim and Norman Geschwind expanded on Wernicke work.[4] This model became the common explanation for conduction aphasia. In this model, there is a lesion in the arcuate fasciculus which connects the two para-Sylvian speech centers. Recent studies have suggested that this is an incomplete model of conduction aphasia in that lesions outside of the arcuate fasciculus can also lead to the clinical presentation of this phenomenon.[5]

Etiology

Lesions in Broca area in the inferior frontal lobe can lead to loss of verbal fluency. Whereas, lesions in the Wernicke area lead to impaired comprehension.  Patients with lesions in either Broca or Wernicke area will have impaired repetition. However, there is a group of patients with relatively intact comprehension and verbal fluency but will display severely impaired repetition. A lesion such as a stroke or a tumor affecting the arcuate fasciculus which connects Broca and Wernicke areas can lead to this condition. More recent evidence suggests that lesions of the left superior temporal gyrus, the left supramarginal gyrus, the left inferior parietal lobe (Brodmann area 40), the left primary auditory cortices (Brodmann area 41 and 42), and the insula, can all lead to this condition.[6] Thus, lesions in multiple areas surrounding the Sylvian fissure may impair repetition. This likely represents the interconnectivity of the language areas of the brain.

Epidemiology

Broca and Wernicke aphasia are relatively common in middle cerebral artery strokes. Pure conduction aphasia which affects only repetition is uncommon. 

Pathophysiology

The area that mediates language in the brain is in the dominant hemisphere. In most people, this is the left hemisphere of the brain. Broca areas reside in the inferior frontal lobe in Brodmann areas 44 and 45. Wernicke area is in the region of the superior temporal gyrus in Brodmann area 22. The arcuate fasciculus connects these two regions. The classical explanation for conduction aphasia is that damage to the arcuate fasciculus impairs the transmission of information between the Wernicke area and the Broca area. This injury leads to impaired repetition. Thus, the patient can comprehend the speech but cannot transmit the information to the speech production centers in the Broca area to allow repetition to occur. Recent research based on the anatomically distributed modular networks model shows that patients with conduction aphasia clinically often have lesions in the supramarginal gyrus or deep parietal matter, which suggests that damage to anatomically related structures may also lead to a disconnection between Broca and Wernicke areas.

History and Physical

The findings in conduction aphasia may be subtle because of the lack of neurological findings. The patient may complain of trouble coming up with words, or making errors when he/she tries to speak. During the assessment of aphasia, the clinician should examine the patient's verbal fluency, comprehension, repetition, reading, writing, and naming. A patient with relatively well-preserved auditory comprehension, fluent speech production, reading, writing, but poor speech repetition may have conduction aphasia. Patients may display well-articulated responses similar to the target word and continue to repeat words or phrases to correct the error (conduit d’approache). The rest of the neurological exam (cranial nerves, motor, sensory, reflexes, gait, coordination) is typically normal.

Evaluation

The finding of conduction aphasia at the bedside suggests the possibility of a lesion in the dominant hemisphere of the brain, specifically the areas that connect the Wernicke and Broca areas. The clinician should perform neuro-imaging to look for a stroke, tumor, infection, or another pathology in the setting of conduction aphasia. CT or MRI of the brain is the first imaging modality of choice. Depending on the results, further testing may be necessary to determine the precise etiology.

Treatment / Management

There is no standard treatment for aphasia. Speech and language therapy is the core mainstay of care for patients with aphasia. The therapist should tailor the treatment to the individual needs of the patient. Conduction aphasia is a relatively mild language impairment, and most patients can return to day-to-day life. No medical or surgical treatment improves the outcome in patients with aphasia. However, if the underlying lesion is an infection or tumor, then removing the offending lesion may prevent the worsening of the deficit.

Differential Diagnosis

Aphasia differs from dysarthria which results from impaired articulation. Dysarthria is a motor dysfunction due to disrupted innervation to the face, tongue, or soft palate that results in slurred speech. Conduction aphasia differs from Wernicke and Broca aphasia in that there is an isolated inability to repeat. Neurodegenerative disorders such as primary progressive aphasia lead to a gradual loss of language function.[7] However, this condition affects all aspects of language. Trans-cortical motor and sensory aphasias do not affect repetition.  Anomic aphasia affects only the ability to name objects and does not affect repetition. 

Prognosis

The prognosis for conduction aphasia depends on the underlying cause. If the cause is a stroke, patients can make a good recovery but may have persistent deficits. Speech therapy may be useful to help remediate the effects of aphasia and restore normal function.

Complications

Aphasia can affect the quality of life in a significant way because communication is in day-to-day life is severely impaired. Communication difficulty may affect a patient's:

• Job
• Relationships
• Day-to-day function

Barriers in communication may lead to social embarrassment, depression, and relationship issues.

Deterrence and Patient Education

Conduction aphasia is less disabling than other types of aphasia. However, it still may cause issues with communication. Education regarding the patient's condition should involve the patient, family, and caregivers.

Pearls and Other Issues

When patients complain of stumbling over words, it is important for clinicians to ask the patient to repeat simple phrases to test for conduction aphasia. The impaired repetition suggests a lesion in the para-Sylvian region of the dominant hemisphere. Therefore, the clinician should get neuro-imaging to look for pathology affecting this region of the brain.

Enhancing Healthcare Team Outcomes

Patients with conduction aphasia may take weeks to months to recover. The patient, family, and caregivers, and the treatment team need to know of the patient's deficits and be supportive of the recovery efforts to maximize recovery. Patients should continue to engage in social and leisure activities to avoid social isolation. Importantly, patients with conduction aphasia rarely have intellectual deficits, but only an isolated difficulty in repetition.