MYASTHENIA (myasthenia; Greek my[s] muscle + astheneia powerlessness, weakness; synonym: asthenic bulbar paralysis, myasthenia gravis pseudoparalytica) — the neuromuscular disease which is characterized by muscular weakness and pathological fatigue. The first description of M. is made in 1879 by Erb. In 1894 F. Jolly established change of electroexcitability of muscles, typical for this disease: the bystry exhaustion of their reduction at repeated irritations faradic current with recovery of excitability after rest which received the name of myasthenic reaction.
The etiology and a pathogeny
M.'s Aetiology is completely not found out. Family cases are described, but hereditary character is not proved. Often M.'s combination to a hyperplasia or a tumor of a thymus comes to light.
Pathogenetic mechanisms connect with neuromuscular block. There are instructions on defect of activity of enzymes of synthesis of acetylcholine. The competitive (kurarepodobny) block of synaptic conduction as a result of binding of a holinoretseptor is the polypeptide cosecreted more probable cause thymus (see). M carry to autoimmune diseases. By means of various immunol. methods it is shown that in blood serum of sick M. there are antibodies to protein of skeletal muscles and epithelial cells of a thymus. Along with a myasthenia — the nosological form, observes myasthenic syndromes at organic diseases of a nervous system of various etiology.
The pathological anatomy
the Pathomorphologic research reveals a hyperplasia or a tumor of a thymus gland more than in 70%. The hyperplasia represents increase in lymphoid elements with existence of little bodies of a thymus (Gassal's little bodies) and can be various expressiveness. Tumors of a thymus at M. are more often high-quality (lymphoepitheliomas), sometimes malignant. Find atrophic and dystrophic changes of separate fibers and infiltration in cross-striped muscles limfogistiotsitarny elements of interstitial fabric. Focal lymphoid infiltrates find also in a myocardium, lungs, a liver, kidneys, adrenal glands. Electronic microscopic examination allowed to establish change of a synaptic gap and postsynaptic structures, in hard cases — - final fracture of synoptic contacts.
Clinical picture of a polimorfn. The beginning of a disease in most cases belongs to 20 — 30 years, however the first symptoms develop in 10% of cases at children's age; the disease can be shown also after 50 years. Women are ill much more often than men. M.'s development preferential subacute or chronic. To start a disease emergence of oculomotor frustration in the form of a ptosis, a diplopia is typical, weakness of facial and chewing muscles is often noted. In some cases the first symptoms are shown from muscles of a throat, a throat (difficulty of swallowing, change of a voice, the speech). Less often M. begins with weakness of cross-striped muscles of extremities and a neck. Lability, dynamism of symptoms with their sharp deterioration during the reading, fixing of a look is characteristic, sometimes at the general exercise stress (a phenomenon of generalization of muscular exhaustion) and with reduction and even their disappearance during rest. The m can be generalized and local (damage of muscles of eyes, drinks, throats, mimic muscles or muscles of a trunk). The generalized form can be with respiratory frustration and without them.
On a current distinguish the progressing form M., myasthenic episodes (myasthenic frustration and long spontaneous remissions, short on time) and myasthenic states (stable defects of myasthenic type throughout considerable term). At children's age of M. the wedge, forms proceeds in the form of the following: inborn, early children's and juvenile. Inborn M. can be shown by weak stir of a fruit, in the post-natal period — weak shout, difficulty of suction, swallowing. The m can be also noted at the children who were born from mothers with M.; in 4 — 6 weeks its symptoms gradually disappear. The early children's form is characterized by rather soft current, preferential local symptoms. Most often juvenile M. occurs at children, edges begins in 11 — 16 years and is shown by generalized frustration. At advanced age males are ill preferential; The M, as a rule, generalized, differs in a rapid current, often is followed by a thymoma.
In addition to the symptoms connected with disturbance of neuromuscular transmission, especially at severe generalized forms M. disturbance of activity of closed glands is noted. Quite often hyperfunction of a thyroid gland, as a rule, comes to light there is an insufficiency of adrenal glands. Changes of electrolytic exchange, in particular a hypopotassemia, are caused by pathology of adrenal glands. The disturbances from cardiovascular system connected partially with decrease in content of potassium (myasthenic heart) are noted, change of activity went. - kish. path, liver. At all patients with a severe form of M. function of external respiration is broken.
Under the influence of the exogenous reasons (flu, acute respiratory diseases is more often, intoxications, a physical or mental overstrain are more rare) or endogenous (endocrine shifts, metabolic disturbances), and sometimes and without them at sick M. there can come the sharp aggravation of symptoms called by myasthenic crisis. The rough block of neuromuscular conductivity as the competitive (kurarepodobny) block, or the block of nonsensitivity, owing to accustoming to antikholinesterazny drugs is the cornerstone of krizovy states at their long reception.
Clinically myasthenic crisis is shown by bystry generalization of myasthenic frustration with the expressed oculomotor and bulbar disturbances. The last can reach degree of bulbar paralysis (myasthenic bulbar paralysis of Erba — Goldflama) with an aphonia, a dysarthtia, a dysphagy. Patients cannot swallow not only food, but also saliva. There is a difficulty of breath — it becomes frequent, superficial. Paresis of a diaphragm, intercostal muscles, and also paralysis of extremities develops. The condition of alarm, the psychomotor excitement which is replaced by slackness, apathy, typical vegetative frustration — a mydriasis, tachycardia, a low pulse, a xeroderma or a hyperhidrosis, paresis of intestines and sphincters is characteristic. Intensity of all symptoms quickly increases, within 10 — 20 min. the acute hypoxia of a brain, a loss of consciousness can sometimes develop and to come a lethal outcome.
Myasthenic crisis should be distinguished from cholinergic), developing at overdose of antikholinesterazny drugs and representing the non-competitive depolyarizatsionny block. Cholinergic crisis resembles myasthenic superficially and is characterized by an aggravation of symptoms, generalization of muscular weakness, emergence or aggravation of bulbar frustration, development of respiratory disturbances. After one of the next receptions of antikholinesterazny drugs there can come the sudden apnoea, cyanosis. Unlike myasthenic crisis, vegetative frustration are expressed by muskarinovy and nicotinic effects: the strengthened sialosis and a bronchorrhea, perspiration, vomiting, a rough peristaltics of intestines, sometimes with a profuse liquid chair, abdominal pains, a frequent urination are observed. Also narrowing of pupils, bradycardia, hypotonia, widespread fastsikulyation in muscles of all body, sometimes spasms are noted. It must be kept in mind that in some cases crisis can have the mixed character when myasthenic and cholinergic symptoms are combined.
the Diagnosis is made on the basis of characteristic complaints to fatigue, strengthening of the available frustration by the evening and at an exercise stress. Existence of myasthenic reaction is important. As confirmation of the diagnosis serves positive prozerinovy test (sharp reduction of symptoms in 30 — 60 min. after introduction of 2,0 — 3,0 ml of 0,05% of solution of a prozerin intramusculary). The differential diagnosis is carried out with trunk encephalitis (see) and tumor of a brainstem, basal meningitis (see), eye form myopathies (see), Mac-Ardla's disease (see. Glycogenoses ).
The m should distinguish from myasthenic syndromes, to the Crimea Lambert's syndrome — Eaton belongs. Symptoms remind it myasthenic fatigue, trunks are shown, as a rule, in muscles of extremities, sometimes. Defect of synaptic conduction in connection with disturbance of release of acetylcholine therefore antikholinesterazny means render weak effect is the cornerstone of process. More often Lambert's syndrome — Eaton develops at a carcinoma of a lung, sometimes at a breast cancer, a prostate gland, an ovary; the diagnosis is made on the basis of characteristic EM G with a phenomenon of «vrabatyvaniye» during the carrying out rhythmic stimulation. The myasthenic syndrome can develop at congenital anomaly of a synapse. Sometimes it is observed at poly-and a dermatomyositis, a side amyotrophic sclerosis and other organic lesions of a nervous system.
Treatment comes down to correction of relative deficit of acetylcholine and suppression of autoimmune process. At the progressing form of a disease at any age operational treatment is carried out — thymectomy (see). At advanced age X-ray radiation of area of a thymus gland can be recommended. Treatment by steroid hormones, sometimes in combination with anabolic hormones and cytostatics is shown long (1 — 1,5 years). All patient appoint antikholinesterazny drugs — prozerin, the ambenonium chloride, Mestinonum (Kalyminum) and others in doses, to-rye are selected especially individually. Extent of compensation under the influence of treatment by these drugs is various — there can be full compensation or only minor improvement after administration of drug. The good effect renders additional purpose of a veroshpiron (200 — 400 mg a day). At myasthenic crisis urgently enter 0,5 — 1,0 ml of 0,05% of solution of a prozerin intravenously and then 2 — 3 ml intramusculary. In the absence of effect and the accruing phenomena of respiratory frustration urgent is necessary intubation (see) or imposing of a tracheostoma (see. Tracheostomy ), carrying out artificial ventilation of the lungs (see. Artificial respiration ) and other resuscitation actions. At cholinergic crisis cancellation of antikholinesterazny means, introduction of 0,5 — 1 ml of 0,1% of solution of atropine intravenously (repeatedly) and subcutaneously — a reaktivator of cholinesterase — a dipiroksim on 1 ml of 15% of solution is necessary; in hard cases imposing of a tracheostoma, hardware breath is shown.
Operational treatment and features of anesthesia
Close connection of M. with pathology of a thymus, a favorable effect of removal of this gland on the course of a disease give the grounds to consider a thymectomy as one of most pathogenetic reasonable methods of treatment
of M. Vpervye a thymectomy for elimination of myasthenic frustration with success F. Zauerbrukh (1912) at the patient with a bazedovy disease executed. However only in 1939 Mr. A. Blalock purposefully made this intervention at the patient with a severe form of M. Since 50th the thymectomy becomes a recognized method of operational treatment of M.
Optimum results are yielded by an operative measure in the first three years from the beginning of a disease; at the heavy, violently progressing form which is followed by bulbar frustration it is carried out also to earlier terms.
Operation is carried out in the conditions of the general anesthesia. Features of the general anesthesia substantially depend on weight and the nature of disease, extent of generalization of process, existence of respiratory frustration, extent of compensation at reception of antikholinesterazny drugs. Carrying out the general anesthesia at patients with a generalized form M is the most difficult. It is connected by hl. obr. with the fact that at them at the phenomena of a bulbar symptom complex are observed insufficiency of function of external respiration, various disturbances of cordial activity (myasthenic heart) relationship gipotalamo - pituitary and adrenal system is broken, Disintoxication and belkovoobrazuyushchy functions of a liver are reduced, the hypopotassemia develops.
Preoperative preparation consists in correction of a hypopotassemia by intravenous administration of solution of potassium chloride. Carry out also an oxygenotherapy (see. Oxygen therapy ) and special complexes of breathing exercises. Premedication on the eve of operation includes purpose of somnolent and antihistaminic drugs in smaller in comparison with standard doses. Use of Seduxenum is contraindicated because of the expressed effect of the central relaxation. For reduction cholinergic effect of antikholinesterazny drugs introduction in 30 min. prior to operation 0,5 — 0,7 ml of 0,1% of solution of atropine subcutaneously is obligatory.
All sick M. as the day before, and in day of operation shall receive doses of antikholinesterazny drugs, usual for them. In an anesthesia apply derivatives to induction barbituric to - you though it is more preferable the anesthetics close to metabolites of an organism (viadril), but in smaller in comparison with standard dosages. The drugs used for providing the main anesthesia shall not aggravate disturbances of neuromuscular conductivity therefore the level of the general anesthesia shall not exceed stages of I 3 — III 1 on Gvedel's classification (see. Anaesthesia ). Ether is contraindicated, to-ry aggravates disturbance of neuromuscular conductivity. Use of gas-narcotic mix of nitrous oxide and oxygen in the ratio no more than 2:1 with addition of drugs for a neyroleptanalgeziya in reduced dosages is possible only at patients with average degree of manifestation of a disease. At the expressed symptoms of a disease, in the presence of bulbar disturbances, and also a thymoma use of the combined electroanesthesia is shown (see. Elektronarkoz ). At the same time use an impulse current lasting impulse of 0,5 ms, with a frequency of 130 Hz, current in amplitude value 30 — 50 ma and from an additional constant component 0,5 ma. Anode electrodes have on mastoids, the doubled cathode — in frontal area. The electroanesthesia is begun at once after an intubation of a trachea against the background of insufflation of protoxidic and oxygen mix in the ratio 2:1 or 1,5:1. Such technique of the general anesthesia provides on only sufficient vegetative protection, but also the best ratio of mediator hormones what promotes bystry escaping of an anesthesia with recovery on the operating table of adequate independent breath.
For muscle relaxation use drugs of the depolarizing type of action, to-rye call the short-term superficial anti-depolarizing block, completely removable prozeriny. Use for such sick true curares is contraindicated since they call the resistant anti-depolarizing block, to-ry badly gives in to a dekurarization. During operation it is reasonable to carry out the Artificial Ventilation of the Lungs (AVL) in the mode normo-or a moderate hyperventilation.
The full median sagittal sternotomy is preferable to an exposure of a thymus, edges gives the chance to execute operation considerably, regardless of an anatomic configuration of a thymus. It is reasonable to cut the fascia covering gland on border with pleural bags, to-rye stupidly shift in the parties that allows to avoid their wound. One of the difficult moments of operation is allocation of the top and bottom shoots of gland leaving highly on a neck or which are going down to roots of lungs. After removal of gland of edge of a breast reduce 3 — 4 separate kapron seams, in a front mediastinum leave a drainage for aspiration wound separated. All patient in 10 — 20 min. prior to the end of operation in one syringe enter 0,5 mg of atropine and 0,75 mg of a prozerin subcutaneously. Intravenous administration of a prozerin is contraindicated because of a possibility of development of cholinergic crisis.
To the patient with the disturbances of external respiration and bulbar disturbances expressed before operation operation is finished with imposing of a tracheostoma for carrying out IVL in the next postoperative period (see). In case of need carrying out IVL in the postoperative period reduce use of antikholinesterazny drugs to the minimum doses that allows to recover sensitivity of a neuromuscular synapse to them and to reduce the period of IVL.
The direct postoperative lethality at M. makes 1-3%.
Full remission or considerable improvement of a state after a thymectomy is observed at 60 — 80% of patients, however improvement not always occurs right after operation, and is frequent in 5 — 7 years.
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