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1、Myasthenia Gravis 重症肌无力,Wang Suobin Department of Neurology Xuanwu Hospital,Muscular Disorders,Disorders of the neuromuscular junction Disorders of muscle fibers,Disorders of the Neuromuscular Junction,Presynaptic membrane（突触前膜） Lambert-Eaton syndrome Botulism Synaptic cleft（突触间隙） Organophosphate in
2、toxication Postsynaptic membrane（突触后膜） Myasthenia gravis,Disorders of Muscle Fibers (Myopathies),Muscular dystrophies Congenital myopathies Membrane myopathies (chanelopathies) Inflammatory myopathies Metabolic myopathies,I. Definition of Myasthenia Gravis,MG is a disorder of the neuromuscular trans
3、mission owing to antibody-mediated attack on acetylcholine receptors(AchR) at neuromuscular junctions. Muscle weakness occurs in association with continuous effort, and improvement with rest .,. Etiology and Pathogenesis,An autoimmune mechanism, operative at the neuromuscular junction Weakness and f
4、atigue are due to the failure of effective neuromuscular transmission.,Neuromuscular junctions,1.Reduced Number of Receptors and the Competitive Activity of Anti-AchR Antibodies,85% of patients with generalized MG（全身型） 60% of those with ocular MG（眼肌型） are positive for anti-AChR antibody.,Muscle AChR
5、 (Adult),Ach Binds AChR,How the antibodies act at the receptor surface of the end plate and impair the neuromuscular transmission?,(1) Block the binding of Ach to the Ach receptors (2) Increase the degradation rate of AchRs. (3) Complement mediated destruction of postsynaptic folds,2.The role of thy
6、mus in pathogenesis of MG,The thymus（胸腺） is an organ that produces cells involved in immune responses. Approximately 15% of MG patients have a tumor of the thymus (thymoma胸腺瘤) And 60% have abnormal enlargement (hyperplasia增生) of the thymus.,Both T and B cells from the myasthenic thymus are particula
7、rly responsive to the AchR, more so than analogous cells from peripheral blood. Moreover, the thymus contains “myoid cells”(resembling striated muscle) that express surface AchRs. Maybe a virus with tropism for thymic cells that have AchRs might injure such cells and induce antibody formation.,. PAT
8、HOLOGY OF MG,1. THYMUS 15% of MG patients have thymoma 60% have hyperplasia of the thymus,2. Pathology of skeletal muscles: In about 50% of patients, muscles contain lymphorrhages, which are focal clusters of lymphocytes near small necrotic foci without perivascular predilection. （淋巴细胞的聚集） The major
9、 abnormalities of the neuromuscular junction in MG include (a) reduced length of the postsynaptic membrane, (b) shortening of the synaptic folds and (c) widening of the synaptic clefts .,. CLINICAL FEATURES OF MG,A. Prevalence: 5/100,000 B. Age: Average age of onset is 20, with a preference for youn
10、g females below the age of 40, but the disease are more common in males over age 40, especially with thymoma,C. Symptoms: the fluctuating nature of myasthenic weakness: 波动性肌无力 The weakness varies in the course of a single day, sometimes within minutes, and it varies from day to day or over longer pe
11、riods. The weakness worsens towards the end of the day（晨轻暮重）. The factors known to increase weakness include exertion, hot temperatures, infections, emotional upsets, certain drugs (for example, aminoglycosides, phenytoin, local anaesthetics), surgery, menses, and pregnancy.,2. the distribution of w
12、eakness: （1）Ocular muscles(levator palpebrae and extraocular muscles) are affected first in about 40% of patients and are ultimately involved in about 85%-ptosis and diplopia （2）Facial or oropharyngeal muscles are affected-dysarthria, dysphagia, and limitation of facial movements (3) Limb and neck w
13、eakness is also common, but in conjunction with cranial weakness. Almost never are the limbs affected alone.,3.weakness is improved by anticholinesterase drugs:抗胆碱酯酶药 D. Signs: Muscle weakness. Muscles wasting is rare. Deep tendon reflexes are intact or may be brisk. There are no objective sensory d
14、eficits.,Myasthenic Crisis 肌无力危象,Myasthenic crisis is an exacerbation of myasthenia leading to paralysis of respiratory muscles that requires an urgent respiratory support. This is usually caused by infections, initial high dose steroid therapy, or an inadequate treatment. Patients should be managed
15、 in an intensive care unit. In addition to respiratory support. Plasmapheresis or intravenous immunoglobulin treatment may be required for prompt control of the disease.,F. Ossermans Original Classification of MG,Based on the severity of the disease 1. Ocular myasthenia, where disease is confined to
16、 ocular muscles. 2. Generalized myasthenia gravis of mild (a) or moderate (b) intensity. 3. Severe generalized. 4. Myasthenic crisis with respiratory failure.,G. Other Types of MG,1. Neonatal MG: 2. Congenital MG 3. Drug Induced MG: Penicillamine. 4. Neuromuscular Junction Blockade (NMJ): Gentamicin and other aminoglycoside antibiotics,. DIAGNOSIS OF MG,A. History and physical examination: 1. Document weakness occurring with continuous effort and recovering with rest. 2. Comm
