Presynaptic membrane lesions cause ACh synthesis/release disorders: such as botulism, hypermagnesemia, myasthenic gravis-like syndrome (Lambert-Eaton myasthenic syndrome)

Abnormal acetylcholinesterase activity/content in the synaptic cleft: e.g. organophosphate poisoning

Postsynaptic membrane AChR lesions: such as myasthenia gravis, American curare poisoning

Hereditary myopathies: muscular dystrophy, hereditary muscle cell membrane ion channelopathies, metabolic myopathies, congenital myopathies

Acquired myopathies: inflammatory myopathies, drug-related myopathies, toxic myopathies, endocrine myopathies

It is more common in women between the ages of 20 and 30, and in men between the ages of 40 and 50 (mostly associated with thymoma); common causes include infection, surgery, trauma, systemic disease, excessive fatigue, pregnancy, and childbirth.

Course of the disease: The onset is insidious and fluctuating (alternating remission and relapse, which is of diagnostic significance); late-stage patients cannot fully recover after rest; most cases persist for years to decades and are maintained by drugs; a few can remit naturally

Morbid fatigue of affected skeletal muscles: symptoms of weakness worsen after activity/exertion and decrease after rest; they are light in the morning and heavy in the evening; the range of affected skeletal muscles cannot be explained by nerve distribution

Distribution and manifestations of affected muscles: All skeletal muscles of the whole body can be affected, but muscles innervated by cranial nerves are often affected first; it often starts with a group of muscles and gradually expands.

Anticholinesterase drugs are effective

adult type

Children's type: Mostly limited to external ophthalmic muscle paralysis, and ptosis of both eyelids may appear alternately (see-saw shape); about 1/4 can be relieved naturally, and only a few cases involve the whole body skeletal muscles

Neonatal type: The mother has MG, which is caused by the transplacental infusion of IgG into the fetus; the child has low crying, weak sucking, low muscle tone, and reduced movements after birth.

MG crisis: accounting for 10%; refers to coughing weakness or even difficulty breathing due to respiratory muscle involvement due to aggravation of one's own condition/improper treatment, requiring ventilator-assisted ventilation; is the main cause of death; triggers: respiratory infection, surgery, childbirth, Pregnancy, mental stress, systemic myopathy, improper drug use; myasthenic crisis, cholinergic crisis, reflexive crisis (see below for details)

Routine hematuria and cerebrospinal fluid examination were normal; routine EMG examination was basically normal; nerve conduction velocity was normal.

Immunological examination: The proportion of lymphocyte subpopulations in peripheral blood is normal, Treg function is abnormal, and B cell antibody secretion ability is enhanced.

Thymus CT/MRI: Thymic hyperplasia and hypertrophy can be seen

Repetitive electrical nerve stimulation (RNES) (diagnostic value): 17 hours after stopping neostigmine, repeatedly stimulate the ulnar nerve and other motor nerves at low and high frequencies; the typical manifestation of MG is that the 5th wave of action potential amplitude is at a lower frequency than the 1st wave Decrease by more than 10% during stimulation or more than 30% during high-frequency stimulation

Single fiber electromyography (SFEMG): Determine whether the action potential time generated by muscle fibers in the same motor unit is prolonged to reflect the function of the nerve-muscle junction; MG typically manifests as prolonged interval time

AChR antibody (characteristic): Serum AChR antibody is obvious in more than 80% of systemic MG; however, the ocular muscle type is mostly not obvious; the antibody titer is not parallel to the severity of clinical symptoms

Other antibodies: Tintin antibody (associated with thymoma), skeletal muscle specific kinase (MusK) antibody, presynaptic membrane receptor (PrsmR) antibody, neurofilament antibody, thyroid antibody

Fatigue test (Jolly test) is positive: ptosis occurs when the patient continues to look up or upper arm ptosis occurs after the arms are continuously raised horizontally, and the patient recovers after resting.

Positive drug test

Thymectomy: suitable for patients with thymic hypertrophy and high AChR-Ab titer, various types of MG with thymoma, systemic MG in young women, and those with unsatisfactory response to anticholinesterase drug treatment

thymus radiotherapy

Anticholinesterase drugs: start with a small dose and gradually increase the dose to maintain daily life; such as pyridostigmine bromide, neostigmine bromide

Glucocorticoids: first-line medication, suitable for various types of MG

Immunosuppressants: Suitable for those who are ineffective/intolerant to glucocorticoids, or who cannot use glucocorticoids due to hypertension, diabetes, or ulcer disease; such as cyclophosphamide, azathioprine

Drugs that are prohibited/used with caution: aminoglycosides, neomycin, polymyxin, paromomycin, quinine, quinidine, morphine, diazepam, phenobarbital, phenytoin, propranolol

Rapid onset of effect but short duration of effect, recurrence of symptoms as antibody levels increase, and severe adverse reactions → only applicable to MG crisis and refractory MG

DMD (most common, most severe)

BMD: Late onset (5-15 years old), slow progression, mild disease (can still walk before 12 years old); myocardium is rarely involved; normal intelligence; long survival (close to normal life span); resistant to muscle atrophy Most of the protein genes have whole-code deletion mutations, and the expression of dystrophin in the skeletal muscle membrane is reduced.

Facial and shoulder girdle muscles: are the first to be affected; pseudohypertrophy of the orbicularis oris muscle causes the lips to become thickened and slightly curled, which is called a "myopathic face"; pseudohypertrophy of the deltoid muscle can be seen; there may be obvious winged shoulders, free shoulders, and hanger-like scapulae.

The disease progresses slowly, gradually involving the trunk and pelvic girdle muscles

Life span is close to normal

Onset between the ages of 10 and 20 years old. The first symptom is pelvic girdle muscle atrophy, and gradually develops lumbar lordosis, ducking, difficulty going upstairs, gastrocnemius pseudohypertrophy, and winging of the scapula; facial muscles are generally not affected.

EDMD: It usually begins between the ages of 2 and 10 years old. The initial manifestation is weakness of the proximal upper limbs and shoulder girdle muscles. After a few years, it gradually affects the pelvic girdle muscles and distal lower limb muscles. Contractures of the neck, elbow, knee, and ankle joints often occur in the early stage. ;Almost always accompanied by varying degrees of heart damage (can cause sudden death)

Oculopharyngeal type: onset usually around 40 years old; first manifests as symmetrical external ophthalmoplegia, followed by dysphagia and dysarthria

Distal type: muscle weakness mainly occurs in the distal parts of the limbs, with the most obvious weakness and atrophy of the extensor muscles.