Metabolic Myopathies

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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