临床运动诱发试验在低钾型周期性瘫痪诊断中的价值

目的 通过观察运动诱发试验后小指外展幅度和肌电图复合肌肉动作电位(compound muscle action potential,CMAP)变化的特点,建立一种在非发作期诊断低钾型周期性瘫痪的新方法.方法 收集确诊为低钾型周期性瘫痪的患者59例,以非周期性瘫痪患者38例作为对照,对小指展肌进行运动诱发试验测定(低钾型周期性瘫痪患者选择发作间期),观察120 min,测定运动诱发前后肌电图CMAP波幅变化的百分比,同时观察小指展肌肌力的变化以及小指外展幅度的变化.结果 在运动结束后120 min,患者组和对照组CMAP波幅下降的百分比M50(M25,M75)]分别为54.1%(43.1%,66.3%)和11.1%(2.0%,21.3%),差异有统计学意义(Z=6.731,P=0.000);小指外展幅度下降百分比M50(M25,M75)]分别为39.4%(26.3%,48.9%)和7.8%(1.3%,13.7%),差异有统计学意义(Z=5.519,P=0.000).运动后小指展肌肌力小于Ⅳ级者在两组分别为96.3%(52/54)和8.6%(3/35,x2=69.2,P=0.000).当采用小指外展幅度下降百分比＞20%作为界值时,诊断周期性瘫痪的敏感度为87.5%,特异度为90.5%.结论 临床运动诱发试验有助于低钾型周期性瘫痪的诊断.

Utility of clinical exercise test in diagnosis of hypokalaemic periodic paralysis

Objective To assess the utility of changes of muscle strength and compound muscle action potential (CMAP) of abductor digiti minimi (ADM) muscle after the exercise test in diagnosis of hypokalaemic periodic paralysis during inter-attack period. Methods Exercise test was applied on 59 patients with hypokalaemic periodic paralysis and 38 control subjects during inter-attack period. The changes of CMAP amplitude, muscle strength and the range of abduction of ADM muscle at 120 minutes after exercise were calculated and compared between the two groups. Results At 120 minutes after exercise, the M50 (M25, M75 ) of decrease in amplitude of CMAP recorded in ADM muscles were 54. 1% ( 43.1%,66. 3% ) in patients with periodic paralysis and 11.1% (2. 0%, 21.3% ) in control subjects(Z =6. 731,P=0.000), M5o(M25,M75) of decrease in range of abduction of ADM muscles were 39.4% (26.3% ,48. 9% ) in patients with periodic paralysis and 7. 8% ( 1.3%, 13.7% ) in control subjects ( Z = 5. 519,P=0. 000). The muscle strength of ADM muscle was less than Ⅳ grade in 96. 3% (52/54) patients with periodic paralysis and 8.6% ( 3/35 ) in control subjects ( x2 = 68.2, P = 0. 000 ). The sensitivity and specificity for decrease in CMAP amplitude ( best cutoff = 30% ) in diagnosis of hypokalaemic periodic paralysis were 87.5% and 93.7%, respectively. The sensitivity and specificity for decrease in range of abduction of ADM muscle ( best cutoff = 20% ) were 87.5% and 90. 5%, respectively. Conclusion Exercise test is recommended to apply on patients with suspected hypokalaemic periodic paralysis during inter-attack period. The decrease in range of abduction of ADM muscle more than 20% at 120 minutes after exercise supports the diagnosis of hypokalaemic periodic paralysis.