Metabolic Myopathies
Disorders that affect energy utilisation in muscles. Most present with progressive muscle weakness and/or decreasing tolerance to exercise.
McArdle’s Disease/Phosphorylase Deficiency:
autosomal recessive (linked to chromosome 11q); M>F
present with exercise intolerance, cramping, easy fatigue during adolescence
if severe myoglobinuria and rhabdomyolysis
serum CK elevated
acute episodes emergency treat with hydration and alkalisation of urine (to prevent renal failure)
long term – gentle aerobic exercise program; awareness of risk of exercise induced rhabdomyolysis; avoidance of strenuous exercise;
Phosphorylase b Kinase Deficiency (PBK):
• autosomal recessive – varying clinical features
• generally in children weakness and hepatomegaly; in adults decreased tolerance to exercise and myoglobinuria
Phosphofructokinase Deficiency (PFK):
• autosomal recessive. M>F; deficiency results in blockage of glycolysis
• present with increased intolerance to exercise, cramps, myoglobinuria
• acute episodes hydration and alkalisation of urine
Caritine Palmityltransferase Deficiency:
• Autosomal recessive. M5x>F. Onset usually in adolescence.
• present with myalgias, myoglobinuria and stiffness triggered by exercise or other stress (eg infection, emotional)
Mitochondrial myopathies:
• mitochondria play a key role in muscle metabolism, so disorders associated to mitochondrial DNA deletions or mutations results in various clinical syndromes
• due to decline in oxidative capacity become exercise intolerant sedentary lifestyle further physical deconditioning
• aerobic training has been shown to increase work capacity
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