Utility of clinical exercise test in diagnosis of hypokalaemic periodic paralysis / 中华神经科杂志

ABSTRACT

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.