Yi Shan Der is a Junior House Officer at the Gold Coast University Hospital in Australia. She completed her medical degree at Monash University in 2017. She is currently in her second year of basic physician training and has a keen interest in undertaking research projects to improve patient care.
Exertional Rhabdomyolysis as a Clinical Manifestation of Fatty Acid Oxidation Metabolism Defect
A 42-year-old female presented with one-day history of severe myalgia and dark urine after prolonged hiking. This was on a background history of myalgias post physical exertion since childhood and one past episode of atraumatic rhabdomyolysis after extreme dieting and clomiphene use. Family history revealed a brother who reported a similar muscle disorder. On presentation, laboratory evaluation showed marked elevation of plasma creatine kinase (85,400). Subsequent acylcarnitine profile by tandem mass spectrometry demonstrated an abnormal pattern consistent with very long-chain acyl-CoA dehydrogenase (VLCAD) deficiency. The patient was advised to have regular glucose intake frequently with exertion, not to miss meals and to keep well hydrated. She was then referred to the Adult Metabolic Service and was placed on medium chain triglyceride (MCTs)-rich diet.
Metabolic myopathy, an uncommon cause of rhabdomyolysis, is a rare condition which develops when there is a mismatch between energy supply and demand in muscle cells due to an underlying defect in glucose, glycogen, lipid or nucleoside metabolism. The heterogenous group of genetic disorders that result from defects in fatty acid oxidation includes VLCAD deficiency. Individuals with an adult onset defect in fatty acid oxidation typically present with exercise or illness induced rhabdomyolysis but may present with weakness and fatigue. The general approach to these patients encompasses prolonged fasting avoidance, a high complex carbohydrate, low fat diet with MCTs and, if needed, essential fatty acid supplementation.
Clinical practice point:
Early recognition of metabolic myopathy as a cause of exertional rhabdomyolysis can lead to improved patient outcomes with early intervention in diet and lifestyle modification.