Carbamazepine-Responsive Double-Negative VGKC-Complex Antibody Isaacs Syndrome—A Case Report and Literature Review

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Abstract

Isaacs syndrome (IS), commonly referred to as acquired neuromyotonia, is a rare condition characterized mainly by voltage-gated potassium channel (VGKC) antibody-mediated syndrome of peripheral nerve hyperexcitability (PNH). Few case reports have documented IS patients in the absence of both leucine-rich glioma inactivated protein 1 (LGI1) and contactin-associated protein-like 2 (CASPR2) antibodies (double negative). We report a rare case of a 34-year-old healthy female, presenting with a 15-year history of paroxysmal leg cramping and stiffness, preceded by generalized hyperhidrosis and palpitations. Physical examination documented hyperhidrosis, myokymia, and hypertrophic calf muscles. Electromyogram revealed myokymic discharges and neuromyotonic discharges—findings classically seen in Isaacs syndrome. To document the presence of autoantibodies against VGKC, serum LGI1 and CASPR2 antibodies were done; however, both turned out to be absent (double negative). Diagnostic tests to search for an autoimmune or a paraneoplastic etiology were done, which also showed unremarkable results. Despite the unrevealing serologic and imaging tests, a diagnosis of Isaacs syndrome was still made due to the presenting clinical features. Full resolution of symptoms was achieved upon initiation of carbamazepine. Absence of an autoimmune and a paraneoplastic syndrome is possible in IS, especially in cases with double-negative autoantibody status. This is the fifth reported case in published literature of such autoantibody status and highlights the vital role of a physician’s clinical acumen when dealing with rare diseases such as Isaacs syndrome. Knowing the cardinal features of a disease as well as the possible phenotypic varieties allows prompt diagnosis and treatment.

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卡马西平反应性 VGKC 复合物抗体双阴性艾萨克综合征--病例报告和文献综述
摘要 艾萨克斯综合征(IS)通常被称为获得性神经肌张力障碍,是一种罕见的疾病,主要特征是电压门控钾通道(VGKC)抗体介导的周围神经过度兴奋综合征(PNH)。很少有病例报道 IS 患者同时缺乏富亮氨酸胶质瘤灭活蛋白 1(LGI1)和接触素相关蛋白样 2(CASPR2)抗体(双阴性)。我们报告了一例罕见病例,患者是一名 34 岁的健康女性,有 15 年的阵发性腿部抽筋和僵硬病史,发病前伴有全身多汗症和心悸。体格检查发现多汗症、肌强直和小腿肌肉肥大。肌电图显示有肌肌性放电和神经肌张力放电,这些症状通常见于艾萨克斯综合征。为了确定是否存在针对 VGKC 的自身抗体,对血清 LGI1 和 CASPR2 抗体进行了检测,但结果显示这两种抗体都不存在(双阴性)。为了寻找自身免疫或副肿瘤病因,还做了诊断性检查,结果也没有发现异常。尽管血清学和影像学检查都没有发现异常,但根据患者的临床特征,还是做出了艾萨克综合征的诊断。开始服用卡马西平后,症状完全缓解。艾萨克综合征可能不伴有自身免疫和副肿瘤综合征,尤其是在自身抗体双阴性的病例中。在已发表的文献中,这是第五例出现这种自身抗体状态的病例,突出表明了医生在处理艾萨克综合征等罕见疾病时临床敏锐性的重要作用。了解一种疾病的主要特征以及可能的表型变异,有助于及时诊断和治疗。
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