The act of speaking involves a highly coordinated sequence of actions of the respiratory musculature, larynx, pharynx, palate, tongue, and lips. These structures are innervated by the vagal, hypoglossal, facial, and phrenic nerves, the nuclei of which are controlled by both motor cortices through the corticobulbar tracts. As with all movements, those involved in speaking are subject to extrapyramidal influences from the cerebellum and basal ganglia. The act of speaking requires that air be expired in regulated bursts and each expiration must be maintained long enough (by pressure mainly from the intercostal muscles) to permit the utterance of phrases and sentences. The current of expired air is then finely regulated by the activity of the various muscles engaged in speech.
Phonation, or the production of vocal sounds, is a function of the larynx, more particularly the vocal cords. The pitch of the speaking or singing voice depends upon the length and mass of the membranous parts of the vocal cords and can be varied by changing their tension; this is accomplished by means of the intrinsic laryngeal muscles, before any audible sound emerges. The controlled intratracheal pressure forces air past the glottis and separates the margins of the cords, setting up a series of vibrations and recoils. Sounds thus formed are modulated as they pass through the nasopharynx and mouth, which act as resonators. Articulation consists of contractions of the pharynx, palate, tongue, and lips, which interrupt or alter the vocal sounds. Vowels are of laryngeal origin, as are some consonants, but the latter are formed for the most part during articulation; the consonants m, b, and p are labial, l and t are lingual, and nk and ng are guttural (throat and soft palate).
Defective articulation (dysarthria) and phonation (dysphonia) are recognized at once by listening to the patient speak during ordinary conversation or read aloud. Contrived test phrases such as "Methodist Episcopal" or attempts at rapid repetition of lingual, labial, and guttural consonants (e.g., la-la-la-la, me-me-me-me, or k-k-k-k) bring out the particular abnormality. Disorders of phonation call for a precise analysis of the voice and its apparatus.
In pure dysarthria or its most severe representation, anarthria, there is no abnormality of the cortical language mechanisms. The patient is able to understand perfectly what is heard and has no difficulty in reading and writing, although he may be unable to utter intelligible words. This is the strict meaning of being inarticulate. Defects in articulation may be subdivided into several types: lower motor neuron (neuromuscular); spastic (pseudobulbar); rigid (extrapyramidal); cerebellar-ataxic; and hypo- and hyperkinetic dysarthrias, each of which is taken up below.
Lower Motor Neuron and Neuromuscular Dysarthria
This pattern of speech is caused by weakness or paralysis of the articulatory muscles, the result usually of disease of the motor nuclei of the medulla and lower pons or their intramedullary or peripheral extensions (lower motor neuron paralysis). In advanced forms of this disorder, the shriveled tongue lies inert and fasciculating on the floor of the mouth, and the lips are lax and tremulous. Saliva constantly collects in the mouth because of dysphagia, and drooling is troublesome. Dysphonia, an alteration of the voice to a rasping monotone because of vocal cord paralysis, is often an additional feature. As this condition evolves, speech becomes slurred and progressively less distinct. There is special difficulty in the enunciation of vibratives, such as r, and as the paralysis becomes more complete, lingual and labial consonants are finally not pronounced at all. In the past, bilateral paralysis of the palate, causing nasality of speech, often occurred with diphtheria and poliomyelitis, but now it occurs most often with progressive bulbar palsy, a form of motor neuron disease (see "Progressive Bulbar Palsy," Chap. 39), and with certain other neuromuscular disorders, particularly myasthenia gravis. Bilateral paralysis of the lips, as occurs in the facial diplegia of the GuillainBarré syndrome or of Lyme disease, interferes with enunciation of labial consonants; p and b are slurred and sound more like f and v. Degrees of both of these abnormalities are also observed in myasthenia gravis, but there are usually additional features of palatal weakness and softening of guttural consonants and nasal air escape.
Spastic (Pseudobulbar) Dysarthria
Diseases that involve the corticobulbar tracts bilaterally, usually a result of vascular, demyelinating, or motor neuron disease (amyotrophic lateral sclerosis), result in the syndrome of spastic bulbar (pseudobulbar) palsy. The patient may have had a clinically inevident vascular lesion at some time in the past, affecting the corticobulbar fibers on one side; however, because the bulbar muscles on each side are innervated by both motor cortices, there may be little or no impairment in speech or swallowing until another stroke occurs involving the other corticobulbar tract at any level. Upon the second stroke, the patient immediately becomes dysphagic, dysphonic, and anarthric or dysarthric, often with paresis of the tongue and facial muscles. This condition, unlike bulbar paralysis from lower motor neuron involvement, entails no atrophy or fasciculations of the paralyzed muscles; instead, the jaw jerk and other facial reflexes usually become exaggerated, the palatal reflexes are retained or increased, and emotional control is impaired (spasmodic, crying, and laughing—the pseudobulbar affective state described in Chap. 25). Amyotrophic lateral sclerosis is a condition in which the signs of spastic and atrophic bulbar palsy are combined.
When the dominant frontal operculum is damaged, speech may be dysarthric, usually without pseudobulbar impairment in emotional control. In the beginning, with vascular lesions, the patient may be mute; but with recovery or in mild degrees of the same condition, speech is notably slow, thick, and indistinct, much like that of partial bulbar paralysis. The terms cortical dysarthria and cortical anarthria, among many others, have been applied to this disorder, which is more closely related to forms of Broca's aphasia than to the dysarthrias being considered in this section. Also, in many cases of partially recovered Broca's aphasia and in the "mini-Broca" syndrome, the patient is left with a dysarthria that may be difficult to distinguish from a pure articulatory defect. Careful testing of other language functions, especially writing reveals the aphasic aspect of the defect.
A severe dysarthria that is difficult to classify, but resembles that of cerebellar disease, may occur with a left hemiplegia, usually the result of capsular or right opercular infarction. It tends to improve over several weeks but initially may be so severe as to make speech incomprehensible (Ropper).
Rigid (Extrapyramidal) Dysarthria
In Parkinson and other extrapyramidal diseases associated with rigidity of muscles, one observes a rather different disturbance of articulation, characterized by rapid mumbling and cluttered utterance and slurring of words and syllables. The voice is low-pitched and monotonous, lacking both inflection and volume (hypophonia), and trailing off in volume at the ends of sentences. Words are spoken hastily and run together in a pattern that is almost the opposite of the slowed pattern of spastic dysarthria. In advanced cases, speech is whispered and almost unintelligible. It may happen that the patient finds it impossible to talk while walking but can speak better if standing still, sitting, or lying down. In the extrapyramidal disorder of progressive supranuclear palsy, the dysarthria and dysphonia tend instead to be spastic in nature.
With chorea and myoclonus, speech may also be affected in a highly characteristic way. Talking is loud, harsh, improperly stressed or accented, and poorly coordinated with breathing (hyperkinetic dysarthria). Unlike the defect of pseudobulbar palsy or Parkinson disease, chorea and myoclonus cause abrupt interruptions of the words by superimposition of involuntary inspirations and movements of bulbar muscles. The abnormality has been described as "hiccup speech," in that the breaks are unexpected, as in singultation. Accompanying grimacing and other movement abnormalities must sometimes be depended upon for diagnosis. The Tourette syndrome of multiple motor and vocal tics is characterized both by startling vocalizations (barking noises, squeals, shrieks, grunting, sniffing, snorting) and by speech disturbances, notably stuttering and the involuntary utterance of obscenities (coprolalia).
Elements of both corticobulbar (spastic) and extrapyramidal speech disturbances are combined in Wilson disease, acquired hepatocerebral degeneration, in Hallervorden-Spatz disease (PKAN, the new and preferable designation based on the kinase that is affected in the disease), and in the form of cerebral palsy called double athetosis. The speech is loud, slow, and labored; it is poorly coordinated with breathing and accompanied by facial contortions and athetotic excesses of tone in other muscles. In diffuse cerebral diseases such as syphilitic general paresis, slurred, tremulous speech is one of the cardinal signs.
This condition is a component of acute and chronic cerebellar lesions. It may be observed in multiple sclerosis and various degenerative disorders involving the cerebellum, or as a sequela of anoxic encephalopathy or heat stroke. The principal features are slowness of speech, slurring, monotony, and unnatural separation of the syllables of words. The coordination of speech and respiration is erratic. There may not be enough breath to utter certain words or syllables, and others are expressed with greater force than intended (explosive speech). Scanning dysarthria, speaking metronomically as if scanning poetry for meter, is another distinctive cerebellar pattern and is most often a result of mesencephalic lesions involving the brachium conjunctivum. However, in some cases of cerebellar disease, especially if there is an element of spastic weakness of the tongue from corticobulbar involvement, there may be only a slurring dysarthria, and it is not possible to predict the anatomy of the lesions from analysis of speech alone. Myoclonic jerks involving the speech musculature may be superimposed on cerebellar ataxia in a number of diseases such as Creutzfeldt-Jakob prion infection and Lance-Adams postanoxic encephalopathy.
This abnormality, characterized by interruptions of the normal rhythm of speech by involuntary repetition and prolongation or arrest of uttered letters or syllables, is a common developmental disorder, discussed in Chap. 28. But as pointed out by Rosenbek and colleagues and by Helm and colleagues, it may appear in patients who are recovering from aphasic disorders and who had never stuttered in childhood. This form of acquired stuttering in adults has some different features from the developmental type in that the repetitions, prolongations, and blocks are not restricted to the initial syllables of words, stuttering occurs at equal frequency for grammatical as for substantive words, there is little adaptation with continued speaking, and is generally unaccompanied by grimacing or associated movements, as happens in some developmental types. These features are discussed in the review by Lundgren and colleagues. Stuttering differs from palilalia, in which there is repetition of a word or phrase with increasing rapidity, and from echolalia, in which there is an obligate repetition of words or phrases.
In many instances, acquired stuttering is transitory; if it is permanent, according to Helm and associates, bilateral cerebral lesions are present. Nevertheless, we have observed some cases in which only a left-sided, predominantly motor aphasia provided the background for acquired stuttering, and others in which stuttering was an early sign of cerebral glioma originating in the left parietal region. Benson also cites patients in whom stuttering accompanied fluent aphasia. The causative lesion in acquired stuttering may be subcortical and even, as in an exceptional case described by Ciabarra and colleagues, located in the pons. The treatment of Parkinson disease with L-dopa and, occasionally, an acquired cerebral lesion may reactivate developmental stuttering. The latter may explain the emergence of stuttering with oddly situated lesions, such as the aforementioned pontine infarct.
A few points should be made concerning the fourth group of speech disorders, i.e., those that are a result of disturbances of phonation. In adolescence, there may be a persistence of the unstable "change of voice" normally seen in boys during puberty. As though by habit, the patient speaks part of the time in falsetto, and the condition may persist into adult life. Its basis is unknown. Probably the larynx is not masculinized, i.e., there is a failure in the spurt of growth (length) of the vocal cords that ordinarily occurs in pubertal boys. Voice training has been helpful.
Paresis of respiratory movements, as in myasthenia gravis, Guillain-Barré syndrome, and severe pulmonary disease, may affect the voice because insufficient air is provided for phonation. Also, disturbances in the rhythm of respiration may interfere with the fluency of speech. This is particularly noticeable in extrapyramidal diseases, where one may observe that the patient tries to talk during part of inspiration as noted earlier. Another common feature of the latter diseases is the reduction in volume of the voice (hypophonia) because of limited excursion of the breathing muscles—the patient is unable to shout or to speak above a whisper. Whispering speech is also a feature of advanced Parkinson disease, stupor, and occasionally concussive brain injury and frontal lobe lesions, but strong stimulation may make the voice audible.
With paresis of both vocal cords, the patient can speak only in whispers. Because the vocal cords normally separate during inspiration, their failure to do so when paralyzed may result in an inspiratory stridor. If one vocal cord is paralyzed as a result of involvement of the tenth cranial nerve by tumor, for example, the voice becomes hoarse, low-pitched, rasping, and somewhat nasal in quality. The pronunciation of certain consonants such as b, p, n, and k is followed by an escape of air into the nasal passages. The abnormality is sometimes less pronounced in recumbency and increased when the head is thrown forward. Prolonged tracheal intubation that causes pressure necrosis of the posterior cricoarytenoid cartilage and the underlying posterior branch of the laryngeal nerve is an increasingly common iatrogenic cause.
Various tremor disorders, but especially severe essential tremor, affect the voice by creating an oscillatory effect on the vocal cords (see Chap. 6 for a full discussion). An unusual form of this disease causes a vibrato voice tremor almost in isolation, but most cases occur in the context of severe generalized essential tremor. As noted below, the pitch of voice may increase and simulate spasmodic dysphonia. Only the most severe cases of Parkinson tremor impart a warbling to the voice but this appears to be from vibration of the body and chest.
Spasmodic ("Spastic") Dysphonia
This is a relatively common condition about which little is known. Spasmodic dysphonia is a better term than the still-appearing spastic dysphonia, as the adjective spastic suggests corticospinal involvement, whereas the disorder is probably of extrapyramidal origin. The authors, like most neurologists, have seen many patients, middle-aged or elderly men and women, otherwise healthy, who lose the ability to speak quietly and fluently. Any attempt to speak results in simultaneous contraction of the speech musculature, so that the patient's voice is strained and speaking requires an effort. The patient sounds as though he were trying to speak while being strangled. Shouting is easier than quiet speech, and whispering is unaltered. Other actions utilizing approximately the same muscles (swallowing and singing) are usually unimpeded.
Spasmodic dysphonia is usually relatively nonprogressive and occurs as an isolated phenomenon, but we have observed exceptions in which it occurs in various combinations with blepharospasm, spasmodic torticollis, writer's cramp, or some other type of segmental dystonia. The nature of spasmodic dysphonia is unclear. As a neurologic disorder, it may be akin to writer's cramp, i.e., a restricted dystonia (see Chap. 6). As mentioned just above, we have at times had difficulty differentiating a severe essential tremor of voice from spasmodic dysphonia. They may even coexist (fortunately, the treatments are similar). An anatomic basis for the condition has not been demonstrated, but careful neuropathologic studies have not been made.
Glottic spasm, as in tetanus, tetany, and certain hereditary metabolic diseases, results in crowing, stridulous phonation.
Speech therapists, observing such a patient strain to achieve vocalization, often assume that relief can be obtained by making the patient relax, and psychotherapists believed at first that a search of the patient's personal life around the time when the dysphonia began would enable the patient to understand the problem and regain a normal mode of speaking. But both these methods have failed without exception. Drugs useful in the treatment of Parkinson disease and other extrapyramidal diseases are practically never effective. Sectioning of one recurrent laryngeal nerve can be beneficial, but recurrence is to be expected. The most effective treatment, comparable to treatment of other segmental dystonias, consists of the injection of 5 to 20 U of botulinum toxin, under laryngoscopic guidance, into each thyroarytenoid or cricothyroid muscle. Relief lasts for several months. Hoarseness and raspiness of the voice is also a result of structural changes in the vocal cords, the result of cigarette smoking, acute or chronic laryngitis, polyps, and laryngeal edema after extubation.