Dysarthria

DYSARTHRIA. - Difficulty in performing the coordinated muscular movements necessary for the articulation of speech; it is caused by anatomical or functional alterations of the effector organs themselves (lips, tongue, palate, pharynx, larynx) or of their central or peripheral innervation apparatus, resulting in paralysis, atrophy, spasm or ataxia of the phonatory muscles. Internal language remains normal, so much so that the dysarthric patient can readily express himself in writing (provided, of course, that a paresis of the right hand does not hinder this). Of varying intensity, d. can reach the point of inability to speak (anarthria).

The phonatory organs receive their innervation from the facial, glossopharyngeal, vagospinal and hypoglossal nerves, all with nuclei of bulbar origin. Motor nerve fibers from the rolandic operculum reach these bulbar nuclei by way of the internal capsule, the pes of the peduncle, and the pons. The innervation is bilateral, that is, each nucleus receives fibers from both hemispheres; only the nucleus of the lower facial receives predominantly contralateral fibers. The verbomotor pathway can therefore be divided into a first corticobulbar neuron and a second bulbomuscular neuron; any lesion of the first or of the second can cause d.

In the case of supranuclear lesions, d. is caused, as a rule, by bilateral foci; this is explained by the bilaterality of the innervation of the phonatory organs. Unilateral lesions can cause transient d. D. can be caused by ataxia of the phonatory organs.

The distinction between d. (and anarthria) and motor aphasia (v. AFASIA) is made on the basis of the following differential data: in the dysarthric patient internal language is well preserved, hence the ability to express himself readily in writing and to understand perfectly spoken and written speech; in the aphasic patient it is the cortical moment of language that is affected, so that disturbances in the comprehension of spoken and written speech frequently occur. The dysarthric patient pronounces all words badly; singing does not improve his articulation in any way; the aphasic patient pronounces some words well and others not at all, having lost their verbal image; often in singing he readily pronounces words that he is then unable to repeat in speech; the same happens with automatized words (invocations, imprecations). The aphasic patient no longer knows how to speak, the anarthric patient can no longer speak (J. Déjérine).

In d. the difficulty of articulation concerns above all the consonants: labials, palatals, dentals, depending on the phonatory organ affected (facial paralysis, bilateral paralysis of the velum palati, of the tongue); a lesion of the inferior laryngeal nerve, which causes paralysis of the ipsilateral vocal cord, makes the pronunciation of vowels difficult. Besides these lesions of individual nerves, certain diseases and syndromes in which d. is a preponderant symptom must be considered. 1) Nuclear lesions: labioglossolaryngeal paralysis or chronic progressive bulbar paralysis, alone or within the picture of amyotrophic lateral sclerosis; speech is slow, devoid of modulations, with a predominant disturbance in the pronunciation of linguals and labials. 2) Supranuclear lesions: a) progressive paralysis (v. DEMENZA PARALITICA PROGRESSIVA) in which speech is drawled, sometimes tending toward scanning with a characteristic transposition of syllables; in advanced cases, sometimes, pronunciation is unintelligible, reduced almost to vowels alone; b) pseudobulbar paralysis, from multiple bilateral cerebral lesions, with d. similar to that of bulbar paralysis but less severe, aphonic voice, nasalized, without modulations. 3) Lesions of the basal nuclei, even without involvement of the corticonuclear pathway (Parkinson's disease, Wilson's disease, status marmoratus, chorea, etc.); in the most common form, Parkinson's disease, the voice is monotonous and often the words are pronounced in a progressively accelerated manner. 4) Ataxia of the phonatory muscles (may be found in multiple sclerosis, in spinocerebellar hereditary ataxia, in cerebellar affections of various kinds), with scanning speech, sometimes explosive. 5) Myasthenia gravis, in which the first words are well articulated, but as soon as fatigue sets in, speech becomes weak, aphonic, indistinct. 6) Myopathy (facio-scapulohumeral type): in severe cases the pronunciation of labials is difficult, as in bilateral facial paralysis.

Romeo Virgili