Department of Neurology, Mayo Clinic, Rochester, MN.
Neurologist. 2021 Sep 7;26(5):175-177. doi: 10.1097/NRL.0000000000000339.
Approximately 39% to 49% of patients with previously diagnosed acetylcholine receptor antibody-negative myasthenia gravis have been found to be muscle-specific tyrosine kinase (MuSK) antibody positive. These patients have a presentation that typically includes oculobulbar weakness, poorer response to cholinesterase inhibitors, and higher risk for acute clinical decompensation that necessitates plasma exchange. MuSK patients can require more aggressive maintenance immunosuppression earlier-on to maintain stability, often with rituximab.
The authors report the case of a 45-year-old woman who presented with months of worsening hoarseness and exertional dyspnea. Laryngoscopy revealed limited abduction of vocal cords bilaterally as the source of the complaint. Examination revealed ophthalmoparesis and fatigable proximal muscle weakness. She was found to have elevated MuSK antibodies that, along with evidence of neuromuscular junction transmission defect on nerve conduction studies, confirmed the diagnosis of MuSK myasthenia gravis. She experienced no improvement with pyridostigmine and decompensated despite receiving oral steroids, requiring intubation. However, she dramatically improved with plasma exchange and has since been doing well on rituximab therapy.
Dysphonia with hoarse quality secondary to vocal cord abduction paresis is a rare presentation of myasthenia gravis, as opposed to the typical flaccid dysarthria seen in bulbar myasthenia and should raise suspicion for MuSK antibody positivity. MuSK myasthenia gravis cases can be more refractory to treatment with cholinesterase inhibitors and are more likely to cause exacerbations and myasthenia crisis. Therefore, early and accurate diagnosis with appropriate antibody testing is imperative to avoid delays in treatment to prevent potentially life-threatening outcomes.
约 39%至 49%先前诊断为乙酰胆碱受体抗体阴性的重症肌无力患者被发现为肌肉特异性酪氨酸激酶 (MuSK) 抗体阳性。这些患者的表现通常包括眼肌和延髓肌无力，对胆碱酯酶抑制剂的反应较差，以及更易发生急性临床恶化，需要进行血浆置换。MuSK 患者可能需要更早地使用更积极的维持性免疫抑制治疗来维持稳定，通常使用利妥昔单抗。
作者报告了一例 45 岁女性患者，她因数月来声音嘶哑和用力呼吸困难而就诊。喉镜检查显示双侧声带外展受限，这是引起投诉的原因。检查发现眼肌瘫痪和易疲劳的近端肌肉无力。她被发现 MuSK 抗体升高，神经传导研究显示神经肌肉接头传递缺陷的证据，证实了 MuSK 重症肌无力的诊断。她对吡啶斯的明没有改善，尽管接受了口服类固醇治疗，但仍出现失代偿，需要插管。然而，她接受血浆置换后病情显著改善，此后一直接受利妥昔单抗治疗效果良好。
由于声带外展麻痹导致的声音嘶哑是重症肌无力的一种罕见表现，与延髓性重症肌无力中常见的弛缓性构音障碍不同，应怀疑 MuSK 抗体阳性。MuSK 重症肌无力病例对胆碱酯酶抑制剂的治疗反应可能更差，更容易引起恶化和肌无力危象。因此，早期和准确的诊断以及适当的抗体检测至关重要，以避免治疗延误，防止危及生命的后果。
