Feng Yu, Zhang Ying, Liu Zhong-lan, Zhang Chao-dong
Department of Neurology, First Affiliated Hospital of China Medical University, Shenyang, Liaoning, China.
Chin Med J (Engl). 2008 Oct 5;121(19):1915-9.
Normokalaemic periodic paralysis (normoKPP) is characterized by transient and recurrent myoasthenia, and some patients also show muscle stiffness induced by cold exposure (paramyotonia congenita, PMC). It is caused by a mutation in the muscle voltage gated sodium channel alpha subunit (SCN4A) gene. Due to the diversity of the clinical manifestations of patients, it is difficult for clinicians to differentiate some of patients with atypical normoKPP from those who suffer from other periodic paralysis and nondystrophic myotonia. So far, for normoKPP there are almost no ways to assist definite diagnosis besides genetic screening. This research was designed to evaluate an exercise test (ET) in confirming the diagnosis of normoKPP and in assessing the therapeutic effectiveness of some drugs on this disease.
ET, described by McMains, was performed on six subjects from a Chinese family, including four patients with overlapping disease of normoKPP and PMC caused by a mutation of SCN4A Met1592Val that is identified by genetic analysis and two normal control members. The change of compound muscle action potential (CMAP) was recorded. Besides the family, two patients were also tested during treatments with acetazolamide.
All patients showed a slight increase in CMAP immediately after exercise, followed by an abnormal gradual decline, which reached its nadir 25-30 minutes after exercise. CMAP amplitude dropped by more than 40% in patients but less than 23% in controls. In the patients who received treatment with acetazolamide, the change of CMAP amplitude was less than 28% and, at any fixed times, less than pretreatment values.
The ET may be used as a predictive, easy and reliable method of diagnosing normoKPP under conditions without genetic screening help, and is an objective way to evaluate the therapeutic effectiveness. According to different response patterns, the ET may also be helpful in reducing the scope of genetic screening.
正常血钾型周期性麻痹（normoKPP）的特征为短暂且反复发作的肌无力，部分患者还表现出冷暴露诱发的肌肉僵硬（先天性副肌强直，PMC）。它由肌肉电压门控钠通道α亚基（SCN4A）基因突变所致。由于患者临床表现多样，临床医生难以将部分非典型normoKPP患者与其他周期性麻痹及非营养不良性肌强直患者区分开来。迄今为止，除基因筛查外，几乎没有方法可辅助确诊normoKPP。本研究旨在评估一项运动试验（ET）在确诊normoKPP及评估某些药物对该疾病治疗效果方面的作用。
对来自一个中国家庭的6名受试者进行了McMains描述的ET，其中包括4名由基因分析确定为SCN4A基因Met1592Val突变导致的normoKPP和PMC重叠疾病患者以及2名正常对照成员。记录复合肌肉动作电位（CMAP）的变化。除该家庭外，还对2名接受乙酰唑胺治疗的患者进行了测试。
所有患者运动后即刻CMAP均略有升高，随后异常逐渐下降，在运动后25 - 30分钟降至最低点。患者的CMAP波幅下降超过40%，而对照组下降小于23%。接受乙酰唑胺治疗的患者，CMAP波幅变化小于28%，且在任何固定时间均低于治疗前值。
在无基因筛查帮助的情况下，ET可作为一种预测性、简便且可靠的诊断normoKPP的方法，也是评估治疗效果的客观手段。根据不同的反应模式，ET还可能有助于缩小基因筛查范围。
