[PS19] Parallel Session 19: Neurometabolic Disorder

[PS19-3C-1] Metabolic Myopathy in Pediatric Patients

^○PARVANEH KARIMZADEH (Pediatric Neurology Department, Pediatric Neurology Research Center, Shahid Beheshti University of Medical Sciences, Mofid Children Hospital, Tehran, Iran)

Metabolic myopathies most often present with 2 components: A, Recurrent episodes of acute-onset and reversible muscle dysfunction; B, progressive muscle weakness. The clinical features of metabolic myopathies vary in view of different disorders: Disorders of carbohydrate metabolism (glycogenoses), lipid metabolism (lipidoses) and electron transport chain (mitochondrial). Defects in carbohydrate metabolism result in fatigue within minutes of starting intense exercise but Disorders of lipid metabolism become symptomatic after several hours of sustained exertion. The muscle fatigue in metabolic myopathies has an unpleasant quality not reported by normal individuals. Defects in cellular energy production in infants often give rise to severe multisystem disorders but adult-onset disease is restricted to muscle. Episodic abnormalities, such as fatigue, pain, weakness and rhabdomyolysis, correlate with the underlying defects in energy production. The most characteristic presentation of metabolic myopathies is episodic muscle dysfunction. Premature fatigue, exertional muscle pain, contractures and rhabdomyolysis are seen in attacks of increasing severity. Those metabolic muscle diseases causing progressive weakness tend to have a more non-specific ‘myopathic’ phenotype and are less likely to show attacks of rhabdomyolysis. The importance of carnitine in metabolism is in the regulation of levels of acyl-CoA which cause damage when present in excess. The deficiency of carnitine is secondary to a defect in another enzyme system that results in the overproduction of acyl-CoA or in a deficiency of acyl-CoA clearance.
Exacerbations and fluctuations occur but fatigue, exercise-related symptoms and myoglobinuria are usually absent. The diagnosis is supported by the presence of multiple lipid droplets on muscle histology.