Differential Diagnosis in Neurology

15.9. Aphasia and Apraxia

Broca's Aphasia

The major components of Broca's aphasia are difficulty initiating and articulating speech, non-fluency, and an output of less than 20 words per minute. The phrases are short and have abnormal rhythm, inflection and timbre. The patient utilizes meaningful substantive words with a lack of syntactic language. This agrammatism is noted by a decreased use of prepositions, articles, grammatical modifiers and the use of endings which delineate plurals, possessives and tenses. Patients with anterior aphasia have a specific disturbance in use of syntactic aspects of language. Repetition is abnormal particularly for simple syntactic words and endings.

Comprehension is abnormal particularly for syntactic function words such as the difference between in and on. Confrontation naming is abnormal, but performance is improved with a phonetic or contextual cues. Reading comprehension is impaired due to failure to understand grammatically significant words. Writing is abnormal, out of proportion to weakness, and demonstrates omission of grammatical words and misspelling of substantive words.

Persistent Broca's aphasia is frequently associated with an ideomotor apraxia of the left hand. A significant number of patients demonstrate apraxia in handling objects and for imitation of movement with the left arm and face.

Wernicke's Aphasia

These patients demonstrate fluent verbal output and a normal to increased rate of word production with normal prosody and phrase length. Grammatical structure is nearly normal although there is a lack of substantive words. There are characteristic verbal or semantic paraphasic errors (word substitutions), literal or phonemic paraphasias (consonant errors), and neologisms (nonexistent) word errors. Wernicke's aphasia patients cannot comprehend or repeat spoken language. In some patients comprehension of midline commands may be spared. Naming ability is severely impaired. Reading and writing comprehension may be involved to varying degrees. Some patients are more "word deaf" than "word blind" while others demonstrate the reverse. Some patients with Wernicke's aphasia lack insight to their deficit. A hemiparesis is unusual; a superior quadrantic defect may be present as well as an apraxia on imitation and object handling.

Conduction Aphasia

Patients with conduction aphasia have a fluent verbal output with more literal than verbal and nonlinguistic paraphasic mistakes. The patient's comprehension is preserved to a much greater degree than is the ability to repeat. Naming is impaired due to literal paraphasic substitutions. Reading aloud is performed poorly but comprehension is relatively well preserved. Writing demonstrates omissions, spelling errors and altered sequences of words and letters. Patients may have concomitant paresis, cortical sensory loss, visual field deficits and apraxia on verbal command, imitation and object handling. Most lesions producing conduction aphasia affect the supramarginal gyrus and the arcuate fasciculus.

Transcortical Motor Aphasia

Transcortical motor aphasia is characterized by difficulty in initiating speech. Patients stammer, may be dysarthric but repeat sentences almost flawlessly. Patients have difficulty in naming but have relatively well preserved comprehension. They can read aloud and for comprehension. Writing is performed poorly. Patients frequently suffer a hemiparesis and may demonstrate ideomotor apraxia of the left hand to verbal command. Lesions that cause TCM aphasia have been described in the supplementary motor area or in the frontal lobe high in the lateral convexity above Broca's area or low, anterior to Broca's opercular area.

Transcortical Sensory Aphasia

A transcortical sensory aphasia is similar to Wernicke's aphasia with fluent paraphasic speech and poor comprehension but in contradistinction to Wernicke's aphasia has preserved repetition. These patients have a nominal aphasia and cannot read or write. They may have a concomitant significant hemisensory deficit and visual field deficit with a minimal hemiparesis. These patients frequently have damage of the angular gyrus, second and third temporal gyrus or a border zone ischemic lesion of the parieto-temporal junction.

Mixed Transcortical Aphasia or Isolation of the Speech Area

These patients suffer damage to the anterior and posterior vascular border zone areas. They cannot initiate speech, name objects, follow commands, read or write. Most patients have suffered anoxic injury but a few have been reported with acute carotid occlusion, head trauma and severe cerebral edema.

Global Aphasia

Most patients with global aphasia have suffered damage to the frontal and parietotemporal language areas from carotid occlusion or stem middle cerebral artery embolism. Occasionally an anterior branch MCA occlusion can cause the syndrome but this picture then evolves into a Broca's aphasia. These patients cannot initiate speech, follow commands, read, write, repeat or name. Most patients suffer a concomitant right hemiplegia but some have documented with minimal motor or sensory loss.

Anomic Aphasia

This is the most common aphasia. Patients are unable to find the correct word in spontaneous speech, writing and on confrontation. These patients are fluent, can repeat and comprehend spoken and written language; the ability to find words while writing may be more secure than during speech. In general, patients have concomitant deficits in comprehension and read and write with difficulty. A lesion of the left temporoparietal junction is most characteristic although anomic aphasia has been seen with dominant hemisphere frontal, temporal and parietal lesions. It has rarely been reported following right hemisphere and subcortical pathologies. Brain tumors may cause a slowly progressive anomic aphasia. Anomic aphasia may be seen in neurodegenerative diseases, post head injury, and with metabolic and toxic disorders. In the later situation, patients have evidence of an acute confusional state and writing is more impaired than speaking. Pure anomic aphasia may occur with supramarginal gyrus lesions.

Subcortical Aphasia

Infarction, hemorrhage or a tumor(s) in the caudate putamen and thalamus have produced subcortical aphasias. These aphasias have an acute onset often with initial mutism or cerebral hypophonia. The verbal output is slow and poorly articulated. Some patients demonstrate high pitched slow and poorly articulated speech, spastic dysarthria, while others produce hyperkinetic slurred speech. Naming and reading are relatively well preserved. These aphasias are very similar clinically to those seen after damage to the supplementary motor area or infarction of the anterior cerebral artery territory.

One of the most common entities misdiagnosed as aphasia is mutism which is the total cessation of verbal output. The most common brain areas associated with mutism are frontal, supplementary motor, left thalamic, mesencephalic, and left posterior inferior frontal area of Broca. If a patient can write normal sentences when speech returns, speech will be normal with only a few aphasic errors.

Dysarthria

Motor speech disturbances such as ataxia, hypo or hyperkinetics, spastic or aphemic speech may be misinterpreted as aphasia. Aphasia can only be diagnosed when a disturbance of language function is manifested by incorrect grammar or choice of words is demonstrated. Abnormal phonology, the learned rules for producing the sounds of a specific language occurs only with aphasia.

Aphemia

Aphemic patients have great difficulty with articulation. They can express themselves in written language and fully comprehend written and spoken language. Word choice and syntax are normal. Aphemia is a severe disorder of verbal output. Many patients are mute in the acute stage and demonstrate a transient right hemiparesis. The usual lesions causing aphemia occur either directly in Broca's area or destroy the white matter under the left frontal operculum that destroys the outflow pathways of Broca's area. As the patient recovers, the patient's speech is hypophonic and poorly articulated. Speech is grammatically intact but the prosodic quality is often altered. Lesions of the medial frontal cortex, the supplementary motor area or the cingulate gyrus may simulate aphemia.

Pure Word Deafness

Patients' with pure word deafness cannot comprehend spoken language, but can identify nonverbal sounds. These patients are fluent, able to read and write, but can neither comprehend spoken language nor repeat it. Patients have been reported in which word deafness and Wernicke's syndrome occurs concomitantly: these patients demonstrate a fluent aphasia in which there is a greater deficit in comprehension than in writing. The anatomic lesions that cause severe word deafness are damage to Heschl's gyrus and destruction of the radiations from the medial geniculate body as well as the callosal fibers from the contralateral superior temporal gyrus. This combination of lesions isolates the left hemisphere auditory association cortex from any auditory input. The second localization for the syndrome is bilateral damage to the midportion of the superior temporal gyrus.

Nonverbal auditory agnosia, the inability to recognize nonverbal sounds, occurs with lesions of the right hemisphere. Cortical deafness occurs with bilateral damage to Heschl's gyrus and their connections. In this state, patients are aware of words and sounds but cannot interpret them.

Differential Diagnosis of Aphasia

• Aphemia
• Mutism
• Pure word deafness
• Auditory agnosia
• Cortical deafness
• Dysarthria
• Nonverbal auditory agnosia