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大汉管了一个病人，面部肌肉无力的男性患者， 50岁，疲劳试验阳性，肌电图重频阴性，AChR抗体阴性，考虑重症肌无力，但用了新斯的明之后症状加重了，还出现呼吸困难。病人一生气出院了。大汉却百思不得其姐。大汉来向萌妹子老师请教。 重症肌无力是由于出现针对肌肉终板成分的病理性抗体所致，其特征是波动性肌肉无力。神经肌肉接头示意图如下： （A） AChR和MuSK在神经肌肉接头处表达（B）营养信号传导（C）激活信号传导
肌肉特异性受体酪氨酸激酶（muscle specific receptor tyrosine kinase，MUSK）是一种位于突触后膜表面的蛋白，对于维持AChR正常功能十分重要。MG患者中MUSK抗体阳性的发生率为1％-4％。大汉，你见到的MG分型是这样的：Osserman分型，I眼肌型，IIA轻度全身型，IIB中度全身型，III急性重症型，IV迟发重症型，V肌萎缩型。事实上是这样的：
MuSK-MG亚型通常见于成人，很少出现在老年人或儿童中；lgG4抗体在发病中发挥重要作用，与HLA-DQ5有一定的相关性。其临床表现（余略）看如下文献：
Anti-MuSK antibodies are nearly alwaysassociated with generalized MG, having been seldom reported in patients withsymptoms restricted to extrinsic ocular muscles [20]. Weakness pattern tends tobe more focal than in AChR-MG, with prevalent involvement of bulbar, neck andrespiratory muscles [12,13,16]. The resulting phenotype, mainly consisting ofdysarthria, dysphagia, facial and neck weakness, is rather typical, although notspecific, for MuSK-MG. Ocular symptoms are milder than usually observed in MGpatients and often evolve to symmetrical ophthalmoparesis; limb muscles are involvedto a lesser extent and can be totally spared, although shoulder muscle weaknesscan be an early symptom in few cases. The disease course is often rapidlyprogressive leading, within few weeks from onset, to life-threatening symptomsfrequently culminating in respiratory failure [21]. 抗MuSK抗体几乎总是与广义MG联系在一起，很少有报告出现在有眼外肌受累的病人身上（眼肌常不受累）。与AChR-MG相比，肌无力更容易表现在面部，延髓肌、颈部和呼吸肌广泛受累。典型症状主要包括构音障碍、吞咽困难、面部和颈部的无力，但对于MuSK-MG不具有特异性。眼部症状比通常在MG患者中观察到的要轻，而且经常演变成对称的眼肌瘫痪；肢带肌受累程度较轻，甚至可以完全豁免，尽管在少数情况下肩肌无力是早期症状。该病的病程通常在发病数周内迅速进展，常常导致呼吸衰竭等危及生命的症状。 Twenty-four of 75 patients (32%) in ourseries suffered from myasthenic crises; such a proportion is much higher thanin any other MG subtype in our population, yet in line with the crisis rates(ranging from 25% to 48%) reported by other authors in MuSK-MG [16]. Notably,67% (16/24) of these patients experienced the first crisis within six monthsfrom the onset, and, in two cases, respiratory failure occurred as the presentingsymptom. On the other hand, some patients may have mild to moderatenon-fluctuating weakness or, after thymectomy and steroid treatment, mayachieve stable control of their disease for years; then, they can rapidlyprogress to permanent bulbar symptoms, with severe dysarthria and marked facialweakness. A relatively high frequency of muscle atrophy, particularly offacial, tongue and masseter muscles, has long been recognized as a distinctivefeature of MuSK-MG [22–24]. Although more common in chronic patients, atrophycan be observed at an early stage of the disease [25,26], and can resolve afteraggressive treatment [27]. 32%（其他文献报道为25-48%）的MuSK-MG患者会发展为重症肌无力危象，约67%的患者在起病半年内会经历第一个危象。有两例患者，呼吸衰竭是主要症状。另一方面，部分患者有轻中度的非波动性肌无力，部分在接受胸腺切除术和激素治疗后，可能得到几年的稳定控制，但之后快速地进展为永久的延髓症状、重度构音障碍以及显著的面部肌无力。肌肉萎缩发生率更高，尤其是面部，舌头和咀嚼肌肉；这被作为鉴别MuSK-MG的一个特征。尽管肌肉萎缩常见于慢性疾病患者，但也可见于该病早期，经过积极的治疗可以得到改善。
这时，大汉好像明白了什么……  萌妹子点评：MuSK抗体阳性的重症肌无力
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所有抗
胸腺通常与年龄相符（不伴有胸腺的病理改变），胸腺切除术并不能改善病程
