Aphasia and Other Disorders of Higher Cortical Function

PART III	NEUROLOGIC DISORDERS
11	Aphasia and Other Disorders of Higher Cortical Function

The behavioral neurology syndromes, including the aphasias, are some of the most interesting clinical syndromes to both physicians and laypersons. Popular writings of Oliver Sacks that describe these disorders of higher cortical function are commonly cited as reasons to enter the field of neurology on residency applications. The intellectual appeal of such syndromes is not difficult to understand: The higher cognitive functions are what allow us to carry out essential social activities. From a historical perspective, disorders of language and other cortical functions were among the first to be described as being caused by dysfunction of discrete areas of the brain, giving rise to the concept of cerebral localization in the 19th century.

APHASIA

Aphasia is an acquired disorder of language due to brain dysfunction. It is distinguished from dysarthria, which is a disorder of the mechanical production of speech. Disorders of attention may also masquerade as language disorders, but mental status assessment of the inattentive patient will show dysfunction that extends beyond language. Patients with hearing difficulties may also be misdiagnosed as having aphasia, especially older patients who may not have their hearing aids during hospitalization.

DIAGNOSIS

For the purposes of this chapter, the left hemisphere will be considered the dominant hemisphere for language; this is true in greater than 90% of right-handed people and in 50% of left-handed people. There are several forms of aphasia (Table 11-1) that are classically caused by lesions in specific areas of the brain (Fig. 11-1) and can be distinguished from each other by focused examination of the elements of language such as fluency, comprehension, repetition, and the presence and types of paraphasic errors (Table 11-2). Anomia (an inability to name an object) is seen to some degree in almost all aphasias, so testing confrontation naming is one of the most sensitive screening tests for aphasias—but it is not specific for determining which type of aphasia the patient has. Common items such as a watch or coat are high-frequency objects that are relatively easy for patients to name. Components of these items such as a watch dial or lapel of a coat, however, are lower frequency words and, thus, more sensitive for mild anomia. It is important to note, however, that impaired naming of low-frequency items might also reflect a general knowledge deficit related to the patient’s educational background rather than to an acquired language disorder.

KEY POINTS

●Aphasia is an acquired disorder of language due to brain dysfunction.

●Other causes of impaired communication—including problems with hearing, attention, initiative, or articulation—are not truly aphasias.

●Anomia is seen in almost all types of aphasia.

BROCA APHASIA

Broca aphasia is primarily a disorder of fluent language production. Patients cannot produce phrases of more than a few words, and speech is often described as telegraphic: “me go store.” Content-rich words such as nouns and verbs predominate, whereas connector words such as conjunctions and prepositions are notably absent. Overly used phrases such as “how are you” tend to be preserved in patients with a Broca aphasia. Paraphasic errors (word substitutions) occur often and are usually of the phonemic type, in which sound substitutions are made (e.g., “spool” rather than “spoon”). Patients are aware of and frustrated by their inability to communicate. Comprehension is relatively preserved compared to fluency, but patients have difficulty understanding sentences with complex syntax, such as when the passive voice is used. For example, patients with a Broca aphasia will not be able to understand a sentence such as “on top of the pen, place the paper” but may do better with a sentence such as “put the paper on top of the pen.” Repetition is poor: It may be preserved at the level of individual words, but longer phrases and those with any grammatical complexity prove challenging to repeat.

TABLE 11-1. Aphasias
Type	Fluency	Comprehension	Repetition	Commonly Associated Signs	Lesion Location
Broca	Impaired	Relatively preserved	Impaired	Right hemiparesis (especially face)	Broca’s area (inferior frontal)
Wernicke	Preserved, but often nonsensical or “jargon aphasia”	Impaired	Impaired	Right upper quadrantanopia	Wernicke’s area (superior temporal)
Conduction	Preserved	Preserved	Impaired	Many paraphasic errors	Arcuate fasciculus, insula, temporal isthmus
Transcortical motor	Impaired	Preserved	Preserved. In some cases repetition is the only verbal output	Right hemiparesis	Subcortical, adjacent to Broca area
Transcortical sensory	Preserved	Impaired	Preserved	–	Subcortical, adjacent to Wernicke area
Global	Impaired	Impaired	Impaired	Severe right hemiparesis, gaze deviation to left	Large left hemisphere lesion
Subcortical	Variable	Variable	Variable, often preserved	Hypophonia, often in patients with basal ganglia lesions	Left basal ganglia, thalamus

FIGURE 11-1. Higher cortical (language) centers in the left hemisphere.

Anatomically, a Broca aphasia is associated with lesions in the left posterior–inferior frontal region, also known as Broca’s area. The most common cause of a Broca aphasia is infarction in the superior division of the left middle cerebral artery, but other causes including hemorrhage, tumor, and encephalitis can also produce a Broca aphasia. Because this area of the cerebral cortex is adjacent to the motor cortex, patients with a Broca aphasia often have right-sided weakness that is worse in the face and arm than it is in the leg.

TABLE 11-2. Examination of Language Function
Function	Testing
Fluency	Listen to patient’s spontaneous speech to see if words are strung together into phrases of at least seven words. Overused phrases (e.g., “how do you do?”) do not count.
Repetition	Least challenging: Ask patient to repeat single words Most challenging: Ask patient to repeat syntactically complex sentences, such as “no ifs, ands, or buts about it”
Comprehension	Least challenging: Ask patient to follow simple midline commands, such as “close your eyes” or “open your mouth” Most challenging: Ask patient to follow multistep appendicular commands that cross the midline, such as “point to the ceiling, then touch your left ear with your right hand”
Paraphasic errors	Listen to patient’s spontaneous speech and observe for word substitutions. Phonemic paraphasic errors are substitutions of sounds (e.g., “stadler” instead of “stapler”). Semantic paraphasic errors are substitutions of words in related categories (e.g., “lamp” instead of “flashlight”).
Naming	Least challenging: Ask patient to name high-frequency objects, like watch or tie Most challenging: Ask patient to name low-frequency objects or parts of objects, like dial of watch or lapel
Reading	Ask patient to read written material aloud and to follow written instructions
Writing	Ask patients to write a sentence of their choosing or a sentence dictated by the examiner Simply having patients write their names does not count (it is an overlearned task)

KEY POINTS

●Broca aphasia is primarily a disorder of language production.

●Verbal output in Broca aphasia is nonfluent and telegraphic, with phonemic paraphasic errors. Comprehension is impaired but is relatively preserved for simple phrases. Repetition is poor.

●Anatomically, Broca aphasia is caused by lesions in the left posterior–inferior frontal lobe (Broca’s area).

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