pathological anatomy

1. Myasthenia

2.  Myasthenia gravis ( myasthenia ; Greek my [s] muscle +
astheneia impotence, weakness; synonym: asthenic bulbar
paralysis, myasthenia gravis pseudoparalytica ) is a
neuromuscular disease characterized by muscle weakness
and pathological fatigue. The first description of
Myasthenia was made in 1879 by V. Erb. In 1894, F. Jolly
established a change in the electrical excitability of
muscles typical of this disease: a rapid depletion of their
contraction with repeated stimulation by a faradic current
with restoration of excitability after rest, called the
myasthenic reaction.

3. Etiology and pathogenesis
 The etiology of Myasthenia is not fully understood. Family cases are
described, but hereditary character is not proved. Often a combination of
Myasthenia gravis with hyperplasia or a tumor of the thymus gland is
detected.
 Pathogenetic mechanisms are associated with a block of neuromuscular
transmission. There are indications of a defect in the activity of enzymes for
the synthesis of acetylcholine. A more likely cause is a competitive (curare-
like) block of synaptic conduction as a result of the binding of the
cholinergic receptor by a polypeptide secreted by the thymus
gland (see). Myasthenia gravis is classified as an autoimmune disease. Using
various immunological methods, it has been shown that in the blood serum
of patients with M. there are antibodies to the protein of skeletal muscles
and epithelial cells of the thymus. Along with myasthenia gravis, a
nosological form, myasthenic syndromes are observed in organic diseases of
the nervous system of various etiologies.

4. pathological anatomy
 Pathological examination reveals thymus hyperplasia or
tumor in more than 70%. Hyperplasia is an increase in
lymphoid elements with the presence of thymus bodies
(Hassal bodies) and can be of varying severity. Tumors of the
thymus in M. are often benign (lymphoepithelioma),
sometimes malignant. In striated muscles, atrophic and
dystrophic changes in individual fibers and infiltration by
lymphohistiocytic elements of the interstitial tissue are
found. Focal lymphoid infiltrates are also found in the
myocardium, lungs, liver, kidneys, and adrenal
glands. Electron microscopic examination made it possible
to establish a change in the synaptic cleft and postsynaptic
structures, in severe cases, a complete destruction of
synaptic contacts.

5. Clinical picture
 The clinical picture is polymorphic. The onset of the disease
in most cases refers to 20-30 years, but in 10% of cases the
first symptoms develop in childhood; the disease can
manifest itself after 50 years. Women get sick much more
often than men. M.'s development is predominantly
subacute or chronic. For the onset of the disease, the
appearance of oculomotor disorders in the form of ptosis,
diplopia is typical; weakness of the facial and masticatory
muscles is often noted.

6.  In some cases, the first symptoms are manifested by the
muscles of the pharynx, larynx (difficulty swallowing,
changes in voice, speech). Less commonly, M. begins with
weakness of the striated muscles of the extremities and
neck. Characterized by lability, dynamism of symptoms
with their sharp deterioration when reading, fixing the
gaze, sometimes with general physical activity (the
phenomenon of generalization of muscle fatigue) and with
a decrease and even disappearance of them during
rest. M. can be generalized and local (damage to the
muscles of the eyes, pharynx, larynx, facial muscles or
muscles of the body). The generalized form can be with
and without respiratory disorders.

7.  Along the course, a progressive form of Myasthenia,
myasthenic episodes (short-term myasthenic disorders and
long-term spontaneous remissions) and myasthenic
conditions (stable defects of the myasthenic type for a
significant period of time) are distinguished. At children's
age M. proceeds in the form of the following wedge, forms:
congenital, early children's and juvenile. Congenital M. can
be manifested by weak fetal movement, in the postnatal
period - by a weak cry, difficulty in sucking, swallowing. M.
can also be observed in children born from mothers with
M.; after 4-6 weeks. her symptoms gradually disappear. The
early childhood form is characterized by a relatively mild
course, mostly local symptoms. Most often at children
juvenile M. meets, edges begins at 11 — 16 years and is
shown by generalized frustration. In old age, predominantly
males are ill; M., as a rule, generalized, differs in a fast
current, is often followed by a thymoma.

8.  In addition to the symptoms associated with impaired
neuromuscular transmission, especially in severe
generalized forms of M., there is a violation of the activity
of the endocrine glands. Often revealed hyperfunction of
the thyroid gland, as a rule, there is insufficiency of the
adrenal glands. Changes in electrolyte metabolism, in
particular hypokalemia, are caused by the pathology of the
adrenal glands. There are violations of the cardiovascular
system, associated in part with a decrease in the content of
potassium (myasthenic heart), changes in the activity went.
- kish. tract, liver. In all patients with severe M., the
function of external respiration is impaired

9.  Under the influence of exogenous causes (more often
influenza, acute respiratory infections, less often
intoxication, physical or mental overstrain) or endogenous
(endocrine changes, metabolic disorders), and sometimes
without them, patients with M. may experience a sharp
deterioration in the condition, called myasthenic
crisis. Crisis conditions are based on a gross block of
neuromuscular conduction by the type of a competitive
(curare-like) block, or insensitivity block, due to addiction
to anticholinesterase drugs during their long-term use

10.  Clinically, the myasthenic crisis is manifested by the rapid
generalization of myasthenic disorders with severe
oculomotor and bulbar disorders. The latter can reach the
degree of bulbar palsy (Erb-Goldflam myasthenic bulbar
palsy) with aphonia, dysarthria, dysphagia. Patients cannot
swallow not only food, but also saliva. There is difficulty in
breathing - it becomes frequent, superficial. Paresis of the
diaphragm, intercostal muscles, as well as paralysis of the
limbs develops. Characterized by anxiety, psychomotor
agitation, followed by lethargy, apathy, typical vegetative
disorders - mydriasis, tachycardia, weak pulse, dry skin or
hyperhidrosis, paresis of the intestines and sphincters. The
intensity of all symptoms increases rapidly, sometimes
within 10-20 minutes. may develop acute hypoxia of the
brain,

11.  The myasthenic crisis should be distinguished from the
cholinergic crisis, which develops with an overdose of
anticholinesterase drugs and is a non-competitive
depolarization block. Outwardly, the cholinergic crisis
resembles a myasthenic crisis and is characterized by
deterioration, generalization of muscle weakness, the
appearance or aggravation of bulbar disorders, and the
development of respiratory disorders. After one of the
regular doses of anticholinesterase drugs, sudden
respiratory arrest, cyanosis may occur.

12.  Unlike myasthenic crisis, vegetative disorders are
expressed by muscarinic and nicotine effects: increased
salivation and bronchorrhea, sweating, vomiting, violent
intestinal motility, sometimes with profuse loose stools,
abdominal pain, and frequent urination are
observed. There are also pupillary constriction,
bradycardia, hypotension, widespread fasciculations in
the muscles of the whole body, sometimes convulsions. It
should be borne in mind that in some cases the crisis may
be mixed, when myasthenic and cholinergic symptoms are
combined.