RESUMEN
Background: Hypokalemic Periodic Paralysis, a skeletal muscle disorder, is characterized by muscle weakness often due to lowering of potassium levels in the body. The cause could be due defect in voltage gated calcium or sodium channels caused by genetic defect, thyroid dysfunction, and other secondary reasons. High carbohydrate diet, exercise, alcoholism is known to trigger the symptoms. Methods: 35 patients with non-familial periodic paralysis occurring during summer months in Hyderabad and the neighboring areas were considered in the study. The precipitating factors, onset of symptoms, the type of motor weakness were all taken into account. Biochemical tests like Potassium levels and creatinine phosphokinase were also done. Results: Female preponderance was observes with the prominent age group being 20 -30 years. Most of the patients had sudden onset of symptoms (in less than 6 hours) with all patients having the involvement of the axial, proximal and distal muscles. Hypotonia was seen in 71% of the patients. More than 90% of the patients had lowered potassium levels while majority of them had normal CPK levels. Carbohydrate meal, rest after exercise and alcohol were found to be the most common predisposing factors. Conclusion: As a significant number of people have non-familial and sporadic and potentially reversible causes of hypokalemic paralysis, a proper and detailed work up must be done for other causes of HPP other than familial. Carbohydrate meal, exercise and alcoholism were observed to be the most common causes. Administration and elevation of potassium levels normally reverses the situation.
RESUMEN
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.