Afasia

01Pathophysiology

Language processing in the brain is predominantly a left hemisphere function in over 95% of right-handed individuals and roughly 70% of left-handed individuals. Two cortical regions serve as the primary language centers, connected by a white matter tract called the arcuate fasciculus.

Broca's area, located in the posterior inferior frontal gyrus (Brodmann areas 44 and 45), is responsible for language production and motor programming of speech. It coordinates the planning and sequencing of the motor movements necessary for fluent verbal output. When this area is damaged, the patient knows what they want to say but cannot organize and execute speech smoothly. This is why Broca's aphasia produces effortful, telegraphic, nonfluent speech while comprehension remains relatively intact. Patients are typically aware of and frustrated by their deficit.

Wernicke's area, located in the posterior superior temporal gyrus (Brodmann area 22), is responsible for language comprehension and semantic processing. It decodes the meaning of heard and read language. Damage here disconnects meaning from sound. The patient can still produce fluent-sounding speech because Broca's area is intact, but the output is devoid of meaning, filled with neologisms and paraphasic errors. Because Wernicke's area is also responsible for self-monitoring of speech, these patients are characteristically unaware of their deficit (anosognosia for their language errors).

The arcuate fasciculus is the white matter bundle connecting Wernicke's area to Broca's area, forming the critical relay between comprehension and production. Isolated damage to this tract produces conduction aphasia, in which both comprehension and fluency are preserved, but the patient cannot repeat heard phrases because the comprehension-to-production relay is severed.

The left middle cerebral artery (MCA) supplies all three of these structures. This is why a left MCA stroke is the single most tested cause of aphasia on licensing exams. A proximal left MCA occlusion produces global aphasia (destroying both Broca's and Wernicke's areas), while a superior division occlusion favors Broca's aphasia and an inferior division occlusion favors Wernicke's aphasia.

Transcortical aphasias arise from watershed zone infarcts that damage cortex surrounding (but not including) the primary language centers. Because Broca's area, Wernicke's area, and the arcuate fasciculus are all spared, the defining feature of all transcortical aphasias is preserved repetition despite other language deficits.

02Classification and Clinical Manifestation

The classification of aphasia rests on three bedside parameters: fluency, comprehension, and repetition. A systematic evaluation of these three features allows you to classify the subtype immediately.

Broca's aphasia classically presents as "telegraphic speech": the patient speaks in short, effortful phrases using content words but omitting function words and grammatical markers (e.g., "Want...water...now" instead of "I would like some water now"). Because the lesion often extends into the adjacent precentral gyrus, a right-sided facial droop and arm weakness commonly accompany Broca's aphasia.

Wernicke's aphasia produces fluent but meaningless speech often described as "word salad." The patient speaks at a normal rate and with normal prosody but substitutes incorrect words (semantic paraphasias, e.g., "fork" for "spoon") or creates nonexistent words (neologisms). These patients may be misdiagnosed as psychiatric (delirium or psychosis) if the examiner does not formally assess language.

Conduction aphasia is identified by a striking inability to repeat out of proportion to all other language functions. Patients often make phonemic (literal) paraphasic errors when attempting repetition (e.g., "treen" for "tree") and engage in repeated self-correction attempts called conduite d'approche.

03Diagnostic Workup

In the acute setting, the presentation of aphasia should be treated as stroke until proven otherwise. The first step is always a non-contrast CT of the head to rule out hemorrhagic stroke, because this determines whether the patient is a candidate for thrombolysis. CT may be normal in the first hours of an ischemic event; a normal CT does not exclude stroke.

If CT is negative for hemorrhage and clinical suspicion for ischemic stroke is high, CT angiography is obtained simultaneously or immediately after to evaluate for a large vessel occlusion (especially the left MCA or internal carotid artery), as this determines eligibility for mechanical thrombectomy.

MRI with diffusion-weighted imaging (DWI) is the most accurate test for confirming and localizing an acute ischemic infarct. On DWI, an acute stroke appears as a bright (hyperintense) signal with a corresponding dark signal on the ADC map (restricted diffusion). This is the imaging modality that most precisely maps the lesion to a language area and helps explain the aphasia subtype.

The bedside language examination is performed in parallel and is the tool that classifies the aphasia. The examiner tests:

• Fluency: Ask the patient to describe a picture or speak spontaneously for one minute. Count the phrase length and assess effort.

• Comprehension: Give simple and complex commands ("close your eyes," "point to the ceiling after touching your nose").

• Repetition: Ask the patient to repeat phrases of increasing complexity ("no ifs, ands, or buts").

• Naming: Show common objects (pen, watch, stethoscope) and ask the patient to name them.

For formal quantification and longitudinal tracking, the Western Aphasia Battery is the standardized instrument of choice.

04Management and Treatment

Acute Management

The priority in the first hours is treating the underlying cause, which in most exam scenarios is an acute ischemic stroke. If the patient presents within 4.5 hours of symptom onset and meets eligibility criteria (no contraindications such as active bleeding, recent surgery, or INR >1.7), IV alteplase is the first-line treatment at a dose of 0.9 mg/kg up to a maximum of 90 mg. Ten percent of the total dose is given as an IV bolus over one minute, and the remaining 90% is infused over 60 minutes.

For patients with a confirmed large vessel occlusion on CTA (commonly the left MCA in aphasia), mechanical thrombectomy is indicated up to 24 hours from symptom onset if perfusion imaging demonstrates salvageable brain tissue. This is the single most important intervention for proximal MCA occlusions and can be performed in addition to IV alteplase.

Antiplatelet therapy with aspirin 160-325 mg is started within 24-48 hours but must be delayed at least 24 hours if alteplase was administered. For minor strokes or high-risk TIAs, dual antiplatelet therapy (aspirin plus clopidogrel) for 21 days followed by single antiplatelet therapy reduces recurrence risk.

Long-term Management

Secondary stroke prevention is guided by the underlying etiology. This includes statin therapy (high-intensity, e.g., atorvastatin 40-80 mg daily), blood pressure control to a target of less than 130/80 mmHg, glycemic control if diabetic, and anticoagulation for atrial fibrillation (e.g., apixaban 5 mg twice daily or warfarin with target INR 2.0-3.0).

Speech-language therapy is the cornerstone of aphasia rehabilitation and should begin as early as the patient is medically stable. Evidence supports intensive therapy (at least 5 hours per week) as more effective than lower-intensity regimens. Recovery can continue for months to years, with the greatest gains typically occurring in the first 3-6 months, though meaningful improvement can occur well beyond that window.

For patients with Broca's aphasia, therapy focuses on melodic intonation therapy (MIT), which leverages the intact right hemisphere's musical and prosodic abilities to facilitate speech production. For Wernicke's aphasia, therapy focuses on auditory comprehension drills and use of alternative communication strategies.

05Differential Diagnosis and Distractors

06Traps and High-Yield Pearls

The most common way students lose points on aphasia questions is failing to classify the subtype and instead selecting a generic answer. Exam questions will almost always provide enough information in the vignette for you to determine fluency, comprehension, and repetition status. Students who skip this classification step will confuse Broca's with global aphasia (both are nonfluent, but global aphasia also impairs comprehension) or mistake Wernicke's for a psychiatric condition.

A classic trap is the vignette describing a patient with fluent, nonsensical speech who is "not making sense." Students may be drawn toward answers like "acute psychosis" or "delirium." The discriminator is always acute onset with focal neurological findings (right hemiparesis, right homonymous hemianopia, or right hemisensory loss), which points to a left hemisphere stroke, not a psychiatric condition. Always check the vignette for these focal signs.

Another frequently tested concept is repetition as the key differentiator. When the vignette describes an aphasia that looks like Broca's (nonfluent, intact comprehension) but specifically states that the patient "can repeat phrases," the answer is transcortical motor aphasia, not Broca's. The same logic applies to transcortical sensory versus Wernicke's. Repetition is the single most important discriminating feature between perisylvian and transcortical aphasias.

Students also commonly confuse aphasia and dysarthria. If the vignette says the patient's speech is "slurred" or "unclear" but they can write their thoughts perfectly, that is dysarthria (a motor problem), not aphasia (a language problem). The ability to write normally rules out aphasia.

Finally, remember that anomic aphasia is the mildest form and is also the most common residual aphasia after recovery from any subtype. If a vignette describes a patient several months after a stroke who speaks fluently, comprehends well, repeats normally, but has persistent word-finding difficulty, the answer is anomic aphasia.

The core competency being tested across all aphasia questions is your ability to systematically assess three bedside features (fluency, comprehension, repetition), localize the lesion, and connect the anatomy to the vascular territory. Master the classification table, and you will answer these questions correctly every time.