Corticobasal Degeneration

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CBD, a rare neurodegenerative multisystem disorder of insidious onset, is typically described and characterized by its asymmetric motor signs of limb function abnormalities. We report on the nature, frequency, and severity of speech and language disturbances (see Chapters 18-21).

Neuroanatomical Correlates

A striking feature of CBD is the asymmetry with which the disease presents. Its progressive nature eventually involves extensive and bilateral damage to cortical and basal ganglionic structures. Both the asymmetry and involvement of cerebral cortex and basal ganglia influence motor speech and language disturbances, which increase in severity as the disease progresses. A structural magnetic resonance imaging (MRI) study of 25 patients with CBD (14) found that this series of cases presented almost exclusively with asymmetric posterior frontal and parietal atrophy, which explains the prevalence of motor speech and language disorders owing to perisylvian area involvement. In addition, postmortem studies of basal ganglia abnormalities explain a prevalent finding of hypokinetic features of dysarthria resulting from damage to the extrapyramidal tract (the reader is referred to Chapter 4 for further information regarding neuroanatomical correlates of CBD, PSP, MSA, and Dementia with Lewy bodies).

Speech Disturbances

Dysarthria in CBD is commonly reported (15-18), but with variable dysarthria types including hypokinetic and spastic features primarily and a wide frequency range from 29% to 93%. In their comprehensive review of the literature, Lehman Blake et al. (18) found descriptions of speech or language characteristics in 60 of 66 papers characterizing the features of CBD, representing 457 cases. Across these studies, motor speech disorders were identified in 55% of the cases, with dysar-thria reported in 42% of the cases, nonverbal oral apraxia reported in 4% of the cases, and apraxia of speech reported in 3.9% of the cases.

Among group studies, Riley et al. (15) documented the presence of dysarthria in about half of their 15 cases followed. Wenning and colleagues (16) found dysarthria in 29% of their sample during the first visit (on average 3 [-1.9] yr after onset of symptoms, and 75% of their sample during the last visit (on average 6.1 [-2.0] after onset of symptoms). In the Wenning et al. study, speech abnormalities were variably described as slurred (n = 9), dysphonic (n = 5), mute (n = 5), aphonic (n = 4), unintelligible (n = 4), echolalic (i.e., compulsive and unsolicited complete or partial repetition of other's utterances) (n = 2), or palilalic (i.e., compulsive word and phase repetitions with increased rate usually during spontaneous speech) (n = 1), suggesting that identification of speech characteristics also extended to language abnormalities (i.e., echolalia, and possibly mutism). Frattali and Sonies (17) found dysarthria in 13 (93%) of their sample of 14 cases, therefore documenting dysarthria as a prominent feature of CBD, even in the relatively early phases of disease progression (mean disease duration = 3.5 yr). Using the dysarthria classifications of Darley, Aronson, and Brown (19), dysarthria varied in both type and severity. Of the 13 cases, the majority had mild symptoms, with 7 patients presenting with mild symptoms, 5 with moderate symptoms, and only 1 case with severe symptoms. Five patients (35.7%) had hypokinetic dysarthria, three patients (21.4%) had mixed dysarthria with predominant hypokinetic features, two patients (14.3%) had mixed dysarthria with predominant hyperkinetic features, two patients (14.3%) had mixed dysarthria with predominant spastic features, and one patient (7.1%) had spastic dysarthria. It should be noted that 57% of this clinical sample displayed hypokinetic features of dysarthria—features that characterize the dysarthria of patients with parkinsonism resulting from extrapyramidal damage. This finding provides one explanation for the misdiagnoses of CBD for Parkinson's disease (PD), particularly in early stages. Type or severity of dysarthria did not correlate with duration of disease. Apraxia was also prevalent in this sample, which was assessed in 13 patients. Of this sample, six patients (46%) had orofacial apraxia and five patients (38%) had combined orofacial apraxia and apraxia of speech. Of interest was that none of the patients had apraxia of speech in the absence of orofacial apraxia, but orofacial apraxia presented singly in nearly 50% of this clinical sample. In the most severe cases of oral apraxia, two patients (15.3%) could not voluntarily open their mouths, pucker their lips, or even volitionally perform activities automatic to oral movements (e.g., taking pills, drinking, or eating). The severity of orofacial apraxia for these patients resulted in mechanical interference during their modified barium swallow study procedures. When instructed to look straight ahead, hold bolus in mouth momentarily, and swallow, both patients unintentionally opened their mouths with subsequent loss of bolus from the oral cavity, commenting, "I tried as hard as I could," or "My mouth would not cooperate."

Lehman Blake et al. (18), in their study of 13 autopsy-confirmed cases of CBD, found dysarthria and apraxia of speech in 31% and 38% of their sample, respectively. Of the patients with apraxia of speech, two exhibited nonverbal oral apraxia. Of the patients with dysarthria, dysarthria type was typically mixed, with either spastic or hypokinetic features present in all cases. Lehman Blake and colleagues further found that speech and/or language difficulties were either the first sign, or among the first signs of CBD in 6 (46%) of the 13 patients.

In another study of dysarthria and orofacial apraxia in CBD (20), 9 of the 10 patients followed were mildly dysarthric on the bases of results from administration of the Frenchay Dysarthria Assessment (21). Severity of dysarthria, as assessed by an intelligibility score, correlated with global severity but not with duration of disease. Voluntary movement of the tongue and lips were impaired in all patients. Orofacial apraxia was present in the same nine patients. The apraxia scores, however, did not correlate with the severity of dysarthria, suggesting independent underlying mechanisms. The study concluded that the presence of dysarthria and orofacial apraxia is more frequent in CBD than usually reported.

One study used discriminant analysis to sensitively characterize the variability of dysarthria in 20 patients with atypical parkinsonism (22), resulting in classifications among the three types of hypokinetic, spastic, or ataxic dysarthria for the seven patients with CBD.

An atypical example of a patient with CBD who presented with isolated speech deficits for several years before other symptoms emerged is found in the literature. Bergeron et al. (23) described an unusual presentation in a case with an isolated speech disturbance for 5 yr before developing the more typical features of CBD. The most severe neuroanatomical changes were observed in the left motor cortex and adjacent Broca's area.

Language Disturbances

Aphasia, though included in accounts of the clinical syndrome of CBD, has neither been well described in the literature nor sufficiently studied to determine its clinical frequency, behavioral features, and neuropathological correlates (24). For example, Rinne et al. (25) reported language disturbances to be uncommon in CBD whereas Wenning et al. (16) reported one-third of their 14 patients to have aphasia.

Because of their suspected underreporting in the literature, Frattali et al. (26) attempted to systematically identify and characterize the language deficits of CBD. Based on performance on the Western Aphasia Battery (WAB) (27) and related language and cognitive measures, 53% of the15 patients studied had identifiable aphasia syndromes, including anomic, Broca's, and transcortical motor aphasias. WAB aphasia quotients (100 being normal) ranged from 56.3 to 89.8 (mean = 87.2 ± 12.2) suggesting the presence of mildly to moderately severe aphasia among the cases studied. As aphasia quotients decreased, indicating increasing severity, aphasia classifications changed on an index of fluency, from fluent anomic to nonfluent Broca's or transcortical motor aphasia. None of the patients with aphasia showed predominant receptive aphasic disturbances, suggesting a predominance of frontal involvement. Corroborating these findings, Lehman Blake et al. (18) found aphasia to be present in 7 (54%) of the 13 patients with autopsy-confirmed CBD studied, with aphasia type most often characterized as nonfluent (i.e., agrammatic, telegraphic, reduced phrase length) or anomic.

Recently, a unique behavioral feature of language disturbance, termed yes/no reversals, has been described in CBD among other neurodegenerative diseases (28). For this phenomenon, a patient verbalizes or gestures 'yes' when meaning no, or vice versa, when responding to queries during social discourse. Though not a distinguishable feature of CBD, the prospective arm of this study found its presence in 11 of 34 patients (32%) or nearly one-third of those with CBD (i.e., met the modified diagnostic criteria of Lang et al., ref. 29). Of those who presented with yes/no reversals and for whom MRI data were available (N = 10), 7 had left-hemisphere involvement, suggesting a prominent role of the left hemisphere in this lexically related cognitive sign. Although the phenomenon was dissociated from features of aphasia, correlations of yes/no reversals with frontal lobe functions suggested that higher-order mental disruptions (i.e., mental flexibility and inhibitory control) interacting with motor programming disruptions were associated with the phenomenon.

Consistent with the findings of unusual case presentations depending on lesion topography in CBD (23), an atypical case of progressive sensory aphasia resulting from CBD is found in the literature (30). This patient showed progressive sensory aphasia as an initial symptom, then developed "total aphasia" within 6 yr and finally severe dementia. Neuropathological correlates were found in the cerebral cortex, with the superior and transverse temporal gyri most severely affected, and subsequently in the inferior frontal gyrus. Degeneration of the subcortical gray matter was most severe in the substantia nigra, and it was moderate to mild in the ventral part of the thalamus, globus pallidus, and striatum. A subsequent survey of 28 pathologically evaluated cases of CBD revealed two similar cases, both of which began with progressive aphasia and presented cortical degeneration in the superior temporal gyrus. Also in the literature is a case report of a patient with CBD whose initial symptom was progressive nonfluent aphasia, with the distribution of her cortical lesion at autopsy accentuated in the frontal language-related area (31). In summary, progressive aphasia, either fluent or nonfluent, should be considered among the initial symptoms in CBD.

Clinical Management

The likelihood that speech and language disorders will become prominent features in CBD is high, with the late-stage results severely compromising interpersonal communication. Given this profile, periods of speech-language treatment regimens for the purposes of maintaining functional communication are warranted. Intervention should be tailored to the various stages of decline, beginning with instruction of compensatory strategies (e.g., pacing and overarticulation to improve speech intelligibility, instruction of communication partners to rephrase questions requiring simpler or shorter responses, increasing the salience and structure of context during interactions, and reducing ambient noise in the patient's environments to minimize distractions), proceeding to use of augmentative communication systems (e.g., picture boards, portable voice amplifiers) tailored to the functional use of the patient, and use of multimodality cues to enhance communication (e.g., say it, show it, draw it, point it out). In late stages, the speech-language pathologist can serve as a facilitator to determine what residual communication skills can be used by the patient and can tailor these skills to allow communication of strong preferences or basic need.

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