DYSARTHRIA. – Difficulty in performing the coordinated muscular movements necessary for the articulation of speech; it is caused by anatomical or functional alterations affecting the effector organs themselves (lips, tongue, palate, pharynx, larynx) or their central or peripheral innervation systems, resulting in paralysis, atrophy, spasm, or ataxia of the phonatory muscles. Internal language remains normal, so much so that the dysarthric patient may express himself fluently in writing (of course, when this is not hindered by paresis of the right hand). Of varying intensity, d. may reach the point of inability to speak (anarthria).
The phonatory organs receive their innervation from the facial, glossopharyngeal, vagus-spinal, and hypoglossal nerves, all with a nucleus of bulbar origin. Motor nerve fibres from the Rolandic operculum reach these bulbar nuclei by way of the internal capsule, the cerebral peduncle, and the pons. Innervation is bilateral, that is, each nucleus receives fibres from both hemispheres; only the nucleus of the lower facial nerve receives predominantly contralateral fibres. The verbomotor pathway can therefore be divided into a first cortico-bulbar neuron and a second bulbo-muscular neuron; any lesion of the first or second may cause d.
In the case of supranuclear lesions, d. is generally caused by bilateral foci; this is explained by the bilateral innervation of the phonatory organs. Unilateral lesions may cause transient d. D. may 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 findings: in the dysarthric patient, internal language is well preserved, hence the ability to express himself fluently in writing and to understand spoken and written language perfectly; in the aphasic patient, the cortical phase of language is affected, so that disorders in the comprehension of spoken and written language frequently occur. The dysarthric patient pronounces all words poorly; singing does nothing to improve their articulation; the aphasic patient pronounces some words well and others not at all, having lost their verbal image; often, when singing, he pronounces fluently words that he is subsequently unable to repeat in speech; the same occurs with automatized words (invocations, imprecations). The aphasic patient no longer knows how to speak, whereas the anarthric patient is no longer able to speak (J. Déjérine).
In d., the difficulty of articulation concerns above all the consonants: labials, palatals, and dentals, according to the phonatory organ affected (facial paralysis, bilateral paralysis of the soft palate, or of the tongue); a lesion of the inferior laryngeal nerve, causing paralysis of the ipsilateral vocal cord, makes the pronunciation of vowels difficult. In addition to these lesions of individual nerves, certain diseases and syndromes must be considered in which d. is the predominant symptom. 1) Nuclear lesions: labio-glosso-laryngeal paralysis, or chronic progressive bulbar paralysis, alone or in the context of amyotrophic lateral sclerosis; speech is slow and devoid of modulation, with predominant impairment of the pronunciation of linguals and labials. 2) Supranuclear lesions: a) progressive paralysis (v. DEMENZA PARALITICA PROGRESSIVA), in which speech is slurred, sometimes tending toward scanning, with characteristic transposition of syllables; in advanced cases, pronunciation is at times unintelligible, reduced almost exclusively to vowels; b) pseudobulbar paralysis, resulting from multiple bilateral cerebral lesions, with d. similar to that of bulbar paralysis, but less severe; the voice is aphonic and nasalized, without modulation. 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 the words are often pronounced with progressively increasing rapidity. 4) Ataxia of the pho-
natory muscles (it may occur in multiple sclerosis, hereditary spinocerebellar ataxia, and cerebellar disorders of various kinds), with scanning speech, sometimes explosive. 5) Myasthenia gravis, in which the first words are well articulated, but, as soon as fatigue begins, speech becomes weak, aphonic, and indistinct. 6) Myopathy (facioscapulohumeral type): in severe cases, pronunciation of the labials is difficult, as in bilateral facial paralysis.