Laryngeal neuromuscular dysfunction: causes, symptoms, diagnosis, treatment

The larynx is the functional center of the upper respiratory tract, which reacts subtly to minor disturbances in its innervation, endocrine dysfunctions, various types of psychogenic factors, and professional and domestic hazards.

In this article we will focus on those pathological conditions of the larynx in which certain neuromuscular disorders are most clearly manifested.

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Sensory dysfunctions of the larynx

These dysfunctions include hyperesthesia, paresthesia and hypoesthesia of the mucous membrane, which can occur for a variety of reasons - local inflammatory and neoplastic processes, endocrine dysfunctions, secondary complications of a number of common infectious diseases, neuroses and hysteria.

Hyperesthesia and paresthesia of the larynx in the overwhelming majority of cases occur in inflammatory diseases of the mucous membrane and its lymphoid apparatus, as well as in malignant and benign tumors and crises of tabes dorsalis. As a rule, such changes in the sensitivity of the mucous membrane of the larynx are accompanied by similar symptoms from the laryngopharynx and trachea. A sign of hyperesthesia of the larynx is an increased sensitivity of the specified anatomical formations to a variety of factors that normally do not cause any unpleasant sensations. These signs include pain, itching, and a sore throat caused by factors coming from both the outside (with inhaled air, drinks, food) and the inside, when these factors enter through the mucous membrane of the upper respiratory tract and the gastrointestinal tract. External factors may include dry or humid, hot or cold air, an insignificant content of smoke particles or vapors of various volatile substances, a number of aromatic compounds, etc. etc. Irritation by these substances provokes a painful dry cough. Endogenous factors, along with substances dissolved in the lymph and blood, also include mucus secreted by the mucous glands of the upper respiratory tract and containing antigen-like substances that have entered it from the blood and lymph, which is especially characteristic of attacks of bronchial asthma.

Laryngeal paresthesia

Laryngeal paresthesia is characterized by the occurrence of atypical sensations in the larynx, different from pain or itching, arising not only and not so much from the effect of any substances, but more often "genuinely", spontaneously in the form of a lump in the throat, a sensation of stenosis or, on the contrary, a "free tube", i.e. "a sensation in which there is no sensation" of air passing through the upper respiratory tract. Most often, such paresthesia occurs in hysterical personalities or in some mental illnesses. Discomfort, a feeling of stiffness and objective difficulties in phonation, as well as the above-mentioned paresthesia are noted in secondary amyloidosis of the larynx, which occurs as a complication of pulmonary tuberculosis, bronchiectasis and other chronic purulent and specific processes in the body.

Hypoesthesia and anaesthesia of the larynx are rare and are associated with interruption or insufficient conduction of the superior laryngeal nerve, for example, when it is pressed by a tumor or when it is injured. More often, these sensory disorders occur when the nucleus of this nerve or its supranuclear conduction pathways and the corresponding sensory cortical zones are damaged.

Laryngeal paralysis and paresis

Laryngeal paralysis and paresis are neuromuscular diseases of this organ. They can occur as a result of organic lesions of the motor nerves that innervate the internal muscles of the larynx, or be functional in nature in various neuropsychiatric disorders.

Laryngeal paralysis and paresis are divided into myogenic, neurogenic and psychogenic. Myogenic or myopathic laryngeal paralysis, which depends only on pathological changes in the muscles, is observed very rarely and can be caused by some helminthiases (trichinellosis), infectious diseases (tuberculosis, typhoid fever), as well as banal chronic inflammation, congenital myopathy, fatigue as a result of vocal strain, etc.

Myopathic paresis of the larynx

Myopathic paresis is usually bilateral, affecting only the muscles that adduct the vocal folds. This lesion may be combined with weakness of other muscles, such as the respiratory muscles (diaphragm, intercostal muscles). Among myopathic lesions of the laryngeal muscles, paresis of mm. vocales is the most common. With this paresis, an oval gap is formed between the vocal folds during phonation. This form of the gap occurs because the adductor muscles that bring the vocal processes of the arytenoid cartilages together during phonation retain their function, resulting in the posterior ends of the vocal folds coming together, while the vocal muscles do not participate in this process due to their flabbiness.

Myopathic paresis of the vocal muscles manifests itself as hoarseness and weakness of the voice with the loss of its individual timbre coloring. When trying to force the voice, the phenomenon of "blowing" the larynx occurs, which consists in excessive expenditure of the air supply in the lungs for phonation. When talking, patients are forced to interrupt their speech more often than usual for a new breath.

In isolated bilateral paralysis of the lateral cricoarytenoid muscles, the glottis takes the form of an irregular rhombus. Normally, these muscles close the vocal folds along the midline along their entire length and thereby block the lumen of the larynx. In their paralysis, the glottis remains gaping when trying to phonate, which is why the symptom of "blowing" the larynx becomes especially pronounced, the voice loses its sonority, and patients are forced to switch to a whisper due to the significant expenditure of pulmonary air.

In case of paralysis of the only unpaired muscle - the transverse arytenoid muscle - during phonation in the posterior section of the glottis a lumen in the form of a small isosceles triangle is preserved at the level of the vocal processes of the arytenoid cartilages, while the remaining parts of the vocal folds are completely closed. This form of paralysis is the most favorable for both the vocal and respiratory functions of the larynx.

When the vocal muscles and the transverse arytenoid muscle are paralyzed, phonation produces a picture that vaguely resembles an hourglass and is a combination of variants.

When individual fibers of the posterior cricoarytenoid muscles, which provide tension to the vocal folds during phonation, are paralyzed, their non-closure and floating of the free edges occur, the voice becomes rattling, loses its timbre coloring and the ability to intonate high sounds. This phenomenon is easily determined by stroboscopy.

In unilateral paralysis of the posterior cricoarytenoid muscle, which is the only paired muscle that expands the glottis, on inspiration the corresponding vocal fold occupies a median position due to the pull of the adductor muscles; in bilateral paralysis of this muscle, obstruction of the glottis occurs as a result of both vocal folds occupying a median position.

When all the adductors of the larynx are paralyzed, the vocal folds, under the influence of the traction of the posterior cricoarytenoid muscles, take the position of extreme abduction, and phonation is practically impossible, and respiratory excursions of the vocal folds are absent.

Neurogenic paralysis of the internal muscles of the larynx

Neurogenic paralysis of the internal muscles of the larynx is divided into peripheral, caused by damage to the corresponding motor nerves, and central, arising from damage to the bulbar nuclei of these nerves, higher conducting pathways and centers.

Peripheral neurogenic paralysis of the internal muscles of the larynx is caused by damage to the vagus nerve, in particular its branches - the recurrent nerves. The latter, as is known, innervate all the internal muscles of the larynx with the exception of the anterior cricoarytenoid muscles, which stretch the glottis and abduct the vocal folds. The significant length of the recurrent nerves, their direct contact with many anatomical structures that can be affected by various pathological conditions and surgical interventions, their reverse course from the chest cavity to the larynx - all this negatively affects their protection, which increases the risk of their damage. The causes of these injuries may be: for the left recurrent nerve - an aneurysm of the aortic arch, which this nerve bends around, pleural adhesions at the apex of the right lung (for the right nerve), exudative and cicatricial processes in the pericardium and pleura, tumors and hyperplasia of the lymph nodes of the mediastinum, tumors of the esophagus, goiter, thyroid cancer, tumors and lymphadenitis of the cervical lymph nodes (for both nerves).

Neuritis of the recurrent nerve can develop as a result of intoxication in a number of infectious diseases (diphtheria, typhus) and poisoning with alcohol, nicotine, arsenic, lead, etc. Sometimes the recurrent nerve is damaged during strumectomy.

When the recurrent nerve is paralyzed, the posterior cricoarytenoid muscles, which abduct the vocal folds and expand the glottis (risk of acute respiratory obstruction of the larynx and asphyxia), first cease to function, then after some time other internal muscles of the larynx are immobilized, and only after this the vocal folds (in case of unilateral nerve damage - one fold) take a cadaveric position - intermediate between complete adduction and extreme abduction.

This sequence of switching off the internal muscles of the larynx, observed with damage to one or both recurrent nerves and known as the Rosenbach-Semon law, is of great clinical importance, since with simultaneous damage to both recurrent nerves, the adduction of the vocal folds that occurs first leads to a sharp impairment of breathing, often requiring emergency tracheotomy. With unilateral paralysis of the recurrent nerve, the vocal fold initially occupies a median position, remaining motionless. During phonation, a healthy fold adjoins it, and the voice sounds relatively satisfactory. Breathing remains free at rest and with little physical exertion. With the spread of the pathological process to the adductor muscles, the vocal fold moves away from the midline, a concavity appears on it, and then it takes on a cadaveric position. Hoarseness of the voice occurs. Only later, after several months, when compensatory hyperadduction of the healthy fold appears and it begins to fit tightly against the fixed fold during phonation, the voice acquires a normal sound, but vocal function is practically impossible.

Symptoms of acute bilateral paralysis of the recurrent nerves are typical: the patient sits motionless on the bed, leaning his hands on its edge, his face shows an expression of extreme fear, breathing is rare and stridorous, the supraclavicular fossa and epigastric region sink in on inhalation and bulge out on exhalation, the lips are cyanotic, and the pulse is rapid. The slightest physical effort leads to a sharp deterioration in the patient's condition. Only later, when the vocal folds assume a cadaveric position, and this occurs no earlier than after 2-3 days and a gap of no more than 3 mm forms between them, the respiratory function improves somewhat, but physical exertion still causes phenomena of general hypoxia.

Central laryngeal paralysis

Central laryngeal paralysis is caused by bulbar nuclear and supranuclear conduction lesions and can occur with a variety of diseases and lesions of the brain.

Bulbar paralysis of the larynx occurs in progressive muscular atrophy, multiple sclerosis of the cerebral vessels, syringomyelia, tabes dorsalis, progressive bulbar paralysis, hemorrhages, tumors and gummas of the medulla oblongata and other diseases associated with damage to the nuclear formations of the brainstem, as well as the cortical centers of the pyramidal system and somatotopically organized corticobulbar pathways. In the latter case, organic cortical paralysis of the vagus nerve is bilateral due to incomplete crossing of these nerve pathways before they enter the nuclei of the corresponding motor nerves. The said cortical paralysis is caused by hemorrhages, infarct softenings, tumors arising in the corticobulbar pathways and the corresponding motor zones of the cerebral cortex, providing voluntary movements of the internal muscles of the larynx.

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Syndromic laryngeal paralysis

Syndromic laryngeal paralysis usually occurs with various myopathic syndromes, with congenital hypoplasia of neuromuscular synapses, McArdle syndrome, spastic paralysis, with some forms of myotonia, etc.

Myasthenic syndromes resemble the classic form of myasthenia. They are caused by a pathological state of the neuromuscular synapse, i.e. a disorder of excitation transmission from the nerve fiber to the cholinergic structures of the muscle. This condition should be distinguished from myasthenic-like conditions that are not associated with a disorder of synaptic transmission of nerve excitation and are caused by organic lesions of the brain, endocrine glands, and a disorder of carbohydrate and mineral metabolism. Despite the fact that in the latter cases a positive effect is sometimes observed from the introduction of anticholinesterase drugs (proserin, galantamine, physostigmine, etc.), this fact does not indicate true myasthenia, in which the introduction of these drugs gives a significant, albeit temporary, positive effect.

Lambert-Eaton myasthenic syndrome occurs with bronchogenic carcinoma, thyroid gland damage and is characterized by a significant disruption of the release of acetylcholine from vesicles in the presynaptic section, although the amount of this mediator in numerous vesicles is even excessive. The syndrome is more common in men after 40 years of age and may precede the development of the underlying disease. Signs of this syndrome are muscle weakness and muscle atrophy, decreased or lost deep reflexes, pathological fatigue, mainly legs, less often arms. Muscle groups innervated by cranial nerves suffer less often, but when they are involved in the pathological process, certain paresis and paralysis may be observed, including extraocular and intralaryngeal muscles. In the latter case, speech becomes quiet and slurred due to the weakness of the articulatory apparatus. In passing, it should be noted that many “unexplained” cases of hyperacusis arise precisely because of myasthenic damage to the muscles of the tympanic cavity.

Congenital aplasia of the neuromuscular synapse, manifested by myasthenic syndrome, is clearly revealed by electron microscopic examination: synapses in such cases resemble synapses of embryonic muscles. Clinically, pronounced muscle hypotonia is noted, often a decrease or loss of tendon reflexes. The disease is more often observed in women. The use of proserin or galantamine gives a positive effect. The voice of such patients is usually weakened, loud speech or screaming is not possible or is possible only for a short time.

McArdle syndrome occurs in hereditary glycogenosis (Gierke's disease) - a disease determined by a specific disorder of carbohydrate metabolism, leading to a violation of the reversible processes of glycogenolysis and glycogenesis with a simultaneous violation of protein and lipid metabolism. The disease is congenital, extremely rare. Clinical manifestations begin in childhood and are expressed in the fact that after minor physical exertion there is pain in the muscles, their rapid fatigue and weakness, myoglobinuria, late muscular dystrophy, heart failure, often - weakness of smooth muscles. The syndrome is caused by a deficiency of phosphorylase in muscle tissue, as a result of which the breakdown of glycogen is delayed, which accumulates in excess in the muscles.

Myotonia

This type of motor system disease is characterized by a violation of the contractile function of the muscles, expressed in a special condition in which the contracted muscle returns to a state of relaxation with difficulty. This phenomenon is more often observed in striated muscles, but can occur in smooth muscles. An example of such a phenomenon is the symptom of a tonic pupil, which is part of the Eddie syndrome, caused by selective degeneration of the ganglia of the posterior roots of the spinal cord and the ciliary ganglion. The disease manifests itself at the age of 20-30 years by a sluggish reaction of the pupil to light and darkness, a decrease or complete absence of tendon reflexes, moderate hypecotropism. The symptom of a tonic pupil is characterized by the fact that its expansion or constriction after a change in lighting lasts an unusually long time.

Myotonia of voluntary muscles in its pure form is observed in a special disease called congenital myotonia, or Thomsen's disease. The disease is a type of hereditary myopathy with an autosomal type of inheritance. In this disease, no morphological changes are found in the central nervous system and peripheral nervous system. In the pathogenesis of this type of myotonia, the following are important: impaired permeability of cell membranes, changes in ion and mediator exchange in the calcium-troponin-actomyosin link, as well as increased tissue sensitivity to acetylcholine and potassium. The disease usually begins at school age, sometimes its first signs appear immediately after birth, and by 4-5 months, signs of muscle hypertrophy appear. The course is slow, progressing in the first years with subsequent stabilization; it is often first diagnosed during a military medical commission upon entering military service.

The main symptom of the phenomenon of myotonia is a disturbance of movements, consisting in the fact that after a strong contraction of the muscles, their subsequent relaxation is difficult, but with repeated repetition of this movement it becomes more and more free and, finally, normal. After a short period of rest, the phenomenon of myotonia is repeated with the same severity. Myotonic phenomena can spread to the muscles of the face, on which in this case any expression is maintained for an inadequately long time, to the masticatory and swallowing muscles and the internal muscles of the larynx; in the latter cases, difficulties arise in chewing, swallowing and phonation. Chewing movements become slow, swallowing is difficult, and a sudden sharp cry leads to a prolonged closure of the glottis, which slowly opens only after a few seconds. Signs of the disease intensify with cooling of the body or its individual parts, with physical exertion and mental stress.

Objectively, muscle hypertrophy is determined; patients have an athletic build (Hercules symptom), but muscle strength relative to their volume is reduced.

Functional paralysis of the larynx

Functional paralysis of the larynx occurs in neuropsychiatric disorders, hysteria, neurasthenia, traumatic neurosis. The main symptom of functional paralysis of the larynx is "imaginary" aphonia, in which the voice remains sonorous when laughing, coughing, crying, and conversational speech becomes possible only in a whisper. Functional paralysis of the larynx is more often observed in women and occurs as a manifestation of a hysterical attack or severe emotional stress. Often, aphonia that occurs with acute laryngitis in a neurotic continues as functional aphonia for a long time and after the disappearance of all manifestations of inflammation, which should be taken into account by practicing doctors. In these cases, the patient should be referred to a psychotherapist. Functional aphonia, having suddenly appeared, can disappear just as suddenly. This usually happens after a deep, prolonged sleep, a stormy experience of some joyful event, a sudden fright. The sensitivity of the mucous membrane of the pharynx and larynx in functional aphonia is usually reduced, as is the case in most individuals with a hysterical mentality.

Treatment of neuromuscular dysfunctions of the larynx

Treatment of neuromuscular dysfunctions of the larynx is determined by their nature; each of them requires careful diagnostics, sometimes at the level of genetic research methods, complex biochemical methods, metabolic process studies, etc. Only after accurate recognition of the disease, based on the establishment of its etiology and pathogenesis, the patient is referred to the appropriate specialist or to a number of specialists. As for dysfunctions of the larynx, treatment for them is symptomatic.