远端型重症肌无力的临床和电生理观察

Observation of clinical and electrophysiologicai features in patients with distal myasthenia gravis

目的探讨远端型重症肌无力的临床和电生理特点及转归。方法收集2016年10月至2017年3月北京天坛医院就诊的重症肌无力患者，进行详细的神经系统查体、神经传导测定、重复神经电刺激及针极肌电图检测，筛选出远端型重症肌无力患者，分析其临床、电生理特点和对治疗的反应。结果52例确诊的重症肌无力患者中，远端型4例（7．7％）。发病年龄36-64岁，远端肌无力出现于起病当月至病后6年，上肢手部肌肉非均一性受累，1例伴下肢胫前肌受累。重复神经电刺激低频递减程度于远端肌肉重于近端肌肉；受累远端肌的基线复合肌肉动作电位波幅亦轻度降低或波动性降低。患者接受胆碱酯酶抑制剂或激素加胆碱酯酶抑制剂治疗后眼咽部及肢体远近端肌力均改善；电生理复查见基线复合肌肉动作电位波幅增高，重复神经电刺激低频递减减轻，肌源性改变好转。结论少数重症肌无力患者存在相对突出的远端肌肉受累，远端肌肉除重复神经电刺激低频递减显著外，还可出现基线复合肌肉动作电位波幅降低或日间波动。远端型重症肌无力对常规治疗的反应好，其短期预后同常见的以近端受累为主的重症肌无力。

Objective To explore the clinical and electrophysiological features and prognosis of distal myasthenia gravis （MG）. Methods Data of MG patients in Beijing Tiantan Hospital from October 2016 to March 2017 were reviewed, including thorough neurological examinations, nerve conduction studies, repetitive nerve stimulations （RNS） and needle electromyographies. Distal MG patients were included and were analyzed as to their clinical and electrophysiological features and response to treatments. Results Four patients （7.7%） could be classified as distal type among 52 definitely diagnosed MG patients. They had initial symptoms at age 36 to 64 and developed distal limb muscle weakness in the first month to 6 years after the onset of this disease. Hand muscles were preferentially involved in a non-uniform way. And one patient also had leg weakness on his tibialis anterior muscles. RNS showed a more significant decrement at slow rates in distal muscles, compared with proximal muscles. The baseline compound muscle action potentials （CMAP） of the distal affected muscles presented with slightly decreased or fluctuating amplitudes. Their weakness of ocular, hulbar, proximal and distal limb muscles improved generally after administration of acetyleholinesterase inhibitors or steroids plus aeetylcholinesterase inhibitors. Electropbysiologieal reexaminations revealed increased baseline CMAPs, reduced decrement on RNS, and relief of myogenic changes on needle electromyography. Conclusions Relatively prominent distal limb muscle weakness can be found in a minority of MG patients. Besides profound decrement on slow rate RNS, the involved distal muscles may have a characteristic decreased baseline CMAP, sometimes with a diurnal fluctuation. Distal MG responds well to regular treatments. Its short-term prognosis seems similar to that of common MG with proximal predominance.