Study Of Exercise Test In Hypokalemic Periodic Paralysis

Objective: Patients with clinically definite hypokalemic periodic paralysis were enrolled and healthy volunteers served as controls. Muscle power, serum potassium, serum creatase and thyroxine were monitored during the stages of attack. Exercise tests were applied during interphase. The change in CMAP amplitude was then recorded in order to explore the effectiveness of exercise test (ET) in the identifying patients with periodic paralysis and the relevance of muscle power, serum potassium and serum creatase. The goal is to provide a theoretical basis for diagnosing the stage of interphase of hypokalemic periodic paralysis.Methods: We collected clinical data of 30 outpatients with hypokalemic periodic paralysis in our hospital from November 1st 2009 to October 1st 2010. At the same time we collected data of 30 healthy volunteers who served as controls. Muscle power, serum potassium, serum creatase and thyroxine were measured during the stage of attack. Exercise tests were applied during interphase. Statistical methods were then employed to analyze relevant data.Result:(1) muscle power: Muscle power of patients decreased, from grade 1 to grade 4. In the control group, muscle power remained normal.(2) thyroid function: Hyperthyroidism implies an increase in FT3, FT4 and a decrease in TSH. In the patient group, fifteen were diagnosed thyrotoxic hypokalemic periodic paralysis, the other fifteen were diagnosed primary hypokalemic periodic paralysis. Thyroid function is normal in the control group.(3) serum potassium levels: Serum potassium of patients decreased, from 1.1mmol/L to 3.5mmol/L. In the control group, serum potassium is normal at 3.5～5.5mmol/L. The concentration of serum potassium in thyrotoxic hypokalemic periodic paralysis group was (2.19±0.7)mmol/l, which was lower than that in the primary hypokalemic periodic paralysis group (2.8±0.6mmol/l), The difference between the two groups was statistically significant(t =2.175,P <0.05).(4) serum creatase levels: Compared with the controls, serum creatase levels of 24 patients were elevated significantly.(5) exercise test: In patients with periodic paralysis, we see a significant and prolonged decrease of CMAP(compound muscle action potential) amplitude 10 minutes after the end of exercise. In the control group, after exercise CMAP amplitude returned to the baseline value within 20 min. The decrease seen in the patient group was significantly larger than that in control group(P=0.002) The difference between two groups was statistically significant. According to the results of thyroid function, of the 30 patients, 15 cases fall under the category of thyrotoxic hypokalemic periodic paralysis(TPP), while the other fifteen are primary hypokalemic periodic paralysis(PHOPP). In the TPP group, 50 minutes after the end of exercise CMAP amplitude average is 41.8%. In the PHOPP group, 50 minutes after the end of exercise CMAP amplitude average is 45.3%. There is no statistically significant difference between the two groups.(6)correlation analysis of muscle power, serum potassium, serum creatase : there appears to be a significantly positive correlation between serum potassium and muscle power(r=0.533,P<0.05) and negative correlation between serum potassium and serum creatase(r=-0.624,P<0.01).(7)relevance between change of CMAP amplitude and serum potassium, serum creatase, or muscle power :There is no obvious relevance between change of CMAP amplitude and serum potassium, serum creatase, or muscle power( P〉0.01).Conclusion:The exercise test is a highly sensitive, safe and convenient method. It can be used as a confirmative test for the diagnosis of periodic paralysis during asymptomatic period. PH0PP and TPP are chanaelopatihy which have the same abnormal muscle membrane excitability. Serum potassium level is lower, the paralysis and the muscle damage is more acute. There is no obvious relevance between change of CMAP amplitude and serum potassium, serum creatase, or muscle power .The ET result appears to be no correlation between the mode of onset and severity.