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 Guillain-Barré 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.
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 phenomenon has been termed the “bilateral anterior opercular syndrome” and was first recognized by Foix, Chavany, and Marie in 1926. 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. 24). 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 aphasia than to the dysarthrias being considered in this section. Also, in many cases of partially recovered Broca 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.