A new case report of exercise intolerance with hypokalemia in a healthy carrier of cystic fibrosis

摘要

Context. -We report the case of a 19-year-otd soccer player who almost stopped all sports due to cramps and muscle pain that had gradually worsened over 5 years. He was a heterozygous carrier of cystic fibrosis (mutation delta-F508), and his brother carried the homozygous form resulting in a severe symptomatic disease. Methods and results. - Neurological assesment, EMG and calf MRI, venous doppler of the lower limbs, provided no information. The exercise test shows a decrease in VO_(2max) (37.5 mL/minute per kg, i.e. 81% of the theoretical VO_(2max)) while the ventilatory threshold occurred at 43% of the theoretical VO_(2max). Biochemistry shows no clear abnormality, but there was a very strong response of lactate (up to 19.9mmol/L) followed by a rather slow lactate decrease (constant gamma_2 of Freund's model = 0.47 x 10~2/minute [N = 4 to 12]). There was no myoglobinuria. p-hydroxybutyrate/acetoacetate and lactate/pyruvate ratios were within the normal range. However, there was a hypokalemia at 3.3 mmol before exercise, and at high intensity EKG transiently showed a 170deg rightward switch of the QRS axis. Conclusion. -As far as no other clear explanation can be found for these myalgias, we propose for this exercise intolerance with hypokalemia a mechanism similar to that described by M. Rodier in carriers of the cystic fibrosis L206W mutation, in whom a sweat loss of chloride exacerbated by exercise or heat resulted in a secondary hyperaldosteronism with hypokalemia responsible in turn for cramps and myalgia.