What type of aphasia is characterized by nonfluent speech, difficulty with naming, and relatively preserved comprehension, with the ability to repeat phrases without difficulty, in a patient with word-finding difficulty and right hemiparesis?

Transcortical Motor Aphasia

This patient's presentation is most consistent with transcortical motor aphasia, characterized by nonfluent speech, impaired naming, preserved comprehension (follows three-step commands), and crucially, preserved repetition ability.

Clinical Reasoning Algorithm

The key to diagnosing aphasia subtypes involves systematically evaluating three core language functions:

Step 1: Assess Fluency

• This patient is nonfluent (only 2-3 words at a time), which immediately narrows the differential to Broca aphasia or transcortical motor aphasia 1
• Wernicke and transcortical sensory aphasias are excluded because they present with fluent speech 2, 1
• Conduction aphasia typically presents with fluent speech, making it incompatible with this presentation 1

Step 2: Evaluate Repetition

• This patient has intact repetition (repeats "no ifs, ands, or buts" without difficulty), which is the pathognomonic feature distinguishing transcortical motor aphasia from Broca aphasia 1
• Broca aphasia is excluded because repetition is impaired due to damage involving the arcuate fasciculus and perisylvian language arc 3, 4
• The preserved repetition occurs because the perisylvian language arc remains structurally intact in transcortical motor aphasia 1

Step 3: Assess Comprehension

• This patient has preserved comprehension (follows three-step commands across midline), which is characteristic of both Broca and transcortical motor aphasias 1, 5
• This further excludes Wernicke aphasia, where comprehension is severely impaired 2

Anatomical Correlation

Transcortical motor aphasia results from lesions anterior or superior to Broca's area, affecting the supplementary motor area, cingulate gyrus, or prefrontal cortex, while sparing the perisylvian language network 5. The right hemiparesis in this patient suggests involvement of the left frontal lobe motor pathways, consistent with this localization 6.

Critical Distinguishing Feature

The preservation of repetition is the single most important diagnostic criterion that differentiates transcortical motor aphasia from Broca aphasia in patients with nonfluent speech 1. In Broca aphasia, the lesion extends into the operculum, insula, and adjacent structures, damaging the arcuate fasciculus and impairing repetition 3, 4.

Common Pitfall

Clinicians may misdiagnose transcortical motor aphasia as confusion or Broca aphasia if they fail to formally test repetition ability 6. Always assess repetition with complex phrases (like "no ifs, ands, or buts") to distinguish between these nonfluent aphasia subtypes 1.